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Phil Edwards 50b30e0bf3 howto.html: Update list of implemented DRs. 
2001-12-02  Phil Edwards  <pme@gcc.gnu.org>

	* docs/html/ext/howto.html:  Update list of implemented DRs.
	* docs/html/ext/lwg-active.html:  Import R20 from upstream.
	* docs/html/ext/lwg-defects.html:  Import R20 from upstream.

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head><title>C++ Standard Library Active Issues List</title></head>
<body bgcolor="#ffffff" text="#000000">
<table>
<tr>
<td align="left">Doc. no.</td>
<td align="left">J16/01-0052 = WG21 N1337</td>
</tr>
<tr>
<td align="left">Date:</td>
<td align="left">09 Nov 2001</td>
</tr>
<tr>
<td align="left">Project:</td>
<td align="left">Programming Language C++</td>
</tr>
<tr>
<td align="left">Reply to:</td>
<td align="left">Matt Austern &lt;austern@research.att.com&gt;</td>
</tr>
</table>
<h1>C++ Standard Library Active Issues List (Revision 20)</h1>
<p>Reference ISO/IEC IS 14882:1998(E)</p>
<p>Also see:</p>
<ul>
<li>
<a href="lwg-toc.html">Table of Contents</a> for all library issues.</li>
<li>
<a href="lwg-index.html">Index by Section</a> for all library issues.</li>
<li>
<a href="lwg-status.html">Index by Status</a> for all library issues.</li>
<li><a href="lwg-defects.html">Library Defect Reports List</a></li>
<li><a href="lwg-closed.html">Library Closed Issues List</a></li>
</ul>
<p>The purpose of this document is to record the status of issues
which have come before the Library Working Group (LWG) of the ANSI
(J16) and ISO (WG21) C++ Standards Committee. Issues represent
potential defects in the ISO/IEC IS 14882:1998(E) document. Issues
are not to be used to request new features or other extensions. </p>
<p>This document contains only library issues which are actively being
considered by the Library Working Group. That is, issues which have a
status of <a href="lwg-active.html#New">New</a>, <a href="lwg-active.html#Open">Open</a>,
<a href="lwg-active.html#Ready">Ready</a>, and <a href="lwg-active.html#Review">Review</a>. See
<a href="lwg-defects.html">Library Defect Reports List</a> for issues considered defects and
<a href="lwg-closed.html">Library Closed Issues List</a> for issues considered closed.</p>
<p>The issues in these lists are not necessarily formal ISO Defect
Reports (DR's). While some issues will eventually be elevated to
official Defect Report status, other issues will be disposed of in
other ways. See <a href="#Status">Issue Status</a>.</p>
<p>This document is in an experimental format designed for both
viewing via a world-wide web browser and hard-copy printing. It
is available as an HTML file for browsing or PDF file for
printing.</p>
<p>Prior to Revision 14, library issues lists existed in two slightly
different versions; a Committee Version and a Public
Version. Beginning with Revision 14 the two versions were combined
into a single version.</p>
<p>This document includes <i>[bracketed italicized notes]</i> as a
reminder to the LWG of current progress on issues. Such notes are
strictly unofficial and should be read with caution as they may be
incomplete or incorrect. Be aware that LWG support for a particular
resolution can quickly change if new viewpoints or killer examples are
presented in subsequent discussions.</p>
<p>For the most current official version of this document see
<a href="http://www.dkuug.dk/jtc1/sc22/wg21">http://www.dkuug.dk/jtc1/sc22/wg21</a>.
Requests for further information about this document should include
the document number above, reference ISO/IEC 14882:1998(E), and be
submitted to Information Technology Industry Council (ITI), 1250 Eye
Street NW, Washington, DC 20005.</p>
<p>Public information as to how to obtain a copy of the C++ Standard,
join the standards committee, submit an issue, or comment on an issue
can be found in the C++ FAQ at <a href="http://www.research.att.com/~austern/csc/faq.html">http://www.research.att.com/~austern/csc/faq.html</a>.
Public discussion of C++ Standard related issues occurs on <a href="news:comp.std.c++">news:comp.std.c++</a>.
</p>
<p>For committee members, files available on the committee's private
web site include the HTML version of the Standard itself. HTML
hyperlinks from this issues list to those files will only work for
committee members who have downloaded them into the same disk
directory as the issues list files. </p>
<h2>Revision History</h2>
<ul>
<li>R20:
Post-Redmond mailing; reflects actions taken in Redmond. Added
new issues <a href="lwg-active.html#336">336</a>-<a href="lwg-active.html#350">350</a>, of which issues
<a href="lwg-active.html#347">347</a>-<a href="lwg-active.html#350">350</a> were added since Redmond, hence
not discussed at the meeting.
All Ready issues were moved to DR status, with the exception of issues
<a href="lwg-active.html#284">284</a>, <a href="lwg-active.html#241">241</a>, and <a href="lwg-closed.html#267">267</a>.
Noteworthy issues discussed at Redmond include
<a href="lwg-active.html#120">120</a> <a href="lwg-active.html#202">202</a>, <a href="lwg-active.html#226">226</a>, <a href="lwg-active.html#233">233</a>,
<a href="lwg-active.html#270">270</a>, <a href="lwg-active.html#253">253</a>, <a href="lwg-active.html#254">254</a>, <a href="lwg-active.html#323">323</a>.
</li>
<li>R19:
Pre-Redmond mailing. Added new issues
<a href="lwg-active.html#323">323</a>-<a href="lwg-active.html#335">335</a>.
</li>
<li>R18:
Post-Copenhagen mailing; reflects actions taken in Copenhagen.
Added new issues <a href="lwg-defects.html#312">312</a>-<a href="lwg-active.html#317">317</a>, and discussed
new issues <a href="lwg-defects.html#271">271</a>-<a href="lwg-closed.html#314">314</a>.
Changed status of issues
<a href="lwg-defects.html#103">103</a> <a href="lwg-defects.html#118">118</a> <a href="lwg-defects.html#136">136</a> <a href="lwg-defects.html#153">153</a>
<a href="lwg-defects.html#165">165</a> <a href="lwg-defects.html#171">171</a> <a href="lwg-defects.html#183">183</a> <a href="lwg-defects.html#184">184</a>
<a href="lwg-defects.html#185">185</a> <a href="lwg-defects.html#186">186</a> <a href="lwg-defects.html#214">214</a> <a href="lwg-defects.html#221">221</a>
<a href="lwg-defects.html#234">234</a> <a href="lwg-defects.html#237">237</a> <a href="lwg-defects.html#243">243</a> <a href="lwg-defects.html#248">248</a>
<a href="lwg-defects.html#251">251</a> <a href="lwg-defects.html#252">252</a> <a href="lwg-defects.html#256">256</a> <a href="lwg-defects.html#260">260</a>
<a href="lwg-defects.html#261">261</a> <a href="lwg-defects.html#262">262</a> <a href="lwg-defects.html#263">263</a> <a href="lwg-defects.html#265">265</a>
<a href="lwg-defects.html#268">268</a>
to DR.
Changed status of issues
<a href="lwg-defects.html#49">49</a> <a href="lwg-defects.html#109">109</a> <a href="lwg-defects.html#117">117</a> <a href="lwg-defects.html#182">182</a>
<a href="lwg-defects.html#228">228</a> <a href="lwg-defects.html#230">230</a> <a href="lwg-defects.html#232">232</a> <a href="lwg-defects.html#235">235</a>
<a href="lwg-defects.html#238">238</a> <a href="lwg-active.html#241">241</a> <a href="lwg-defects.html#242">242</a> <a href="lwg-defects.html#250">250</a>
<a href="lwg-defects.html#259">259</a> <a href="lwg-defects.html#264">264</a> <a href="lwg-defects.html#266">266</a> <a href="lwg-closed.html#267">267</a>
<a href="lwg-defects.html#271">271</a> <a href="lwg-defects.html#272">272</a> <a href="lwg-defects.html#273">273</a> <a href="lwg-defects.html#275">275</a>
<a href="lwg-defects.html#281">281</a> <a href="lwg-active.html#284">284</a> <a href="lwg-defects.html#285">285</a> <a href="lwg-defects.html#286">286</a>
<a href="lwg-defects.html#288">288</a> <a href="lwg-defects.html#292">292</a> <a href="lwg-defects.html#295">295</a> <a href="lwg-defects.html#297">297</a>
<a href="lwg-defects.html#298">298</a> <a href="lwg-defects.html#301">301</a> <a href="lwg-defects.html#303">303</a> <a href="lwg-defects.html#306">306</a>
<a href="lwg-defects.html#307">307</a> <a href="lwg-defects.html#308">308</a> <a href="lwg-defects.html#312">312</a>
to Ready.
Closed issues
<a href="lwg-closed.html#111">111</a> <a href="lwg-closed.html#277">277</a> <a href="lwg-closed.html#279">279</a> <a href="lwg-closed.html#287">287</a>
<a href="lwg-closed.html#289">289</a> <a href="lwg-closed.html#293">293</a> <a href="lwg-closed.html#302">302</a> <a href="lwg-closed.html#313">313</a>
<a href="lwg-closed.html#314">314</a>
as NAD.
</li>
<li>R17:
Pre-Copenhagen mailing. Converted issues list to XML. Added proposed
resolutions for issues <a href="lwg-defects.html#49">49</a>, <a href="lwg-active.html#76">76</a>, <a href="lwg-active.html#91">91</a>, <a href="lwg-defects.html#235">235</a>, <a href="lwg-defects.html#250">250</a>, <a href="lwg-closed.html#267">267</a>.
Added new issues <a href="lwg-active.html#278">278</a>-<a href="lwg-active.html#311">311</a>.
</li>
<li>R16:
post-Toronto mailing; reflects actions taken in Toronto. Added new
issues <a href="lwg-defects.html#265">265</a>-<a href="lwg-closed.html#277">277</a>. Changed status of issues
<a href="lwg-defects.html#3">3</a>, <a href="lwg-defects.html#8">8</a>, <a href="lwg-defects.html#9">9</a>, <a href="lwg-defects.html#19">19</a>,
<a href="lwg-defects.html#26">26</a>, <a href="lwg-defects.html#31">31</a>, <a href="lwg-defects.html#61">61</a>,
<a href="lwg-defects.html#63">63</a>, <a href="lwg-defects.html#86">86</a>, <a href="lwg-defects.html#108">108</a>,
<a href="lwg-defects.html#112">112</a>, <a href="lwg-defects.html#114">114</a>, <a href="lwg-defects.html#115">115</a>,
<a href="lwg-defects.html#122">122</a>, <a href="lwg-defects.html#127">127</a>, <a href="lwg-defects.html#129">129</a>,
<a href="lwg-defects.html#134">134</a>, <a href="lwg-defects.html#137">137</a>, <a href="lwg-defects.html#142">142</a>,
<a href="lwg-defects.html#144">144</a>, <a href="lwg-defects.html#146">146</a>, <a href="lwg-defects.html#147">147</a>,
<a href="lwg-defects.html#159">159</a>, <a href="lwg-defects.html#164">164</a>, <a href="lwg-defects.html#170">170</a>,
<a href="lwg-defects.html#181">181</a>, <a href="lwg-defects.html#199">199</a>, <a href="lwg-defects.html#208">208</a>,
<a href="lwg-defects.html#209">209</a>, <a href="lwg-defects.html#210">210</a>, <a href="lwg-defects.html#211">211</a>,
<a href="lwg-defects.html#212">212</a>, <a href="lwg-defects.html#217">217</a>, <a href="lwg-defects.html#220">220</a>,
<a href="lwg-defects.html#222">222</a>, <a href="lwg-defects.html#223">223</a>, <a href="lwg-defects.html#224">224</a>,
<a href="lwg-defects.html#227">227</a> to &quot;DR&quot;. Reopened issue <a href="lwg-active.html#23">23</a>. Reopened
issue <a href="lwg-active.html#187">187</a>. Changed issues <a href="lwg-closed.html#2">2</a> and
<a href="lwg-closed.html#4">4</a> to NAD. Fixed a typo in issue <a href="lwg-defects.html#17">17</a>. Fixed
issue <a href="lwg-defects.html#70">70</a>: signature should be changed both places it
appears. Fixed issue <a href="lwg-defects.html#160">160</a>: previous version didn't fix
the bug in enough places.
</li>
<li>R15:
pre-Toronto mailing. Added issues
<a href="lwg-active.html#233">233</a>-<a href="lwg-defects.html#264">264</a>. Some small HTML formatting
changes so that we pass Weblint tests.
</li>
<li>R14:
post-Tokyo II mailing; reflects committee actions taken in
Tokyo. Added issues <a href="lwg-defects.html#228">228</a> to <a href="lwg-defects.html#232">232</a>. (00-0019R1/N1242)
</li>
<li>R13:
pre-Tokyo II updated: Added issues <a href="lwg-defects.html#212">212</a> to <a href="lwg-defects.html#227">227</a>.
</li>
<li>R12:
pre-Tokyo II mailing: Added issues <a href="lwg-defects.html#199">199</a> to
<a href="lwg-defects.html#211">211</a>. Added &quot;and paragraph 5&quot; to the proposed resolution
of issue <a href="lwg-defects.html#29">29</a>. Add further rationale to issue
<a href="lwg-closed.html#178">178</a>.
</li>
<li>R11:
post-Kona mailing: Updated to reflect LWG and full committee actions
in Kona (99-0048/N1224). Note changed resolution of issues
<a href="lwg-closed.html#4">4</a> and <a href="lwg-defects.html#38">38</a>. Added issues <a href="lwg-closed.html#196">196</a>
to <a href="lwg-active.html#198">198</a>. Closed issues list split into &quot;defects&quot; and
&quot;closed&quot; documents. Changed the proposed resolution of issue
<a href="lwg-closed.html#4">4</a> to NAD, and changed the wording of proposed resolution
of issue <a href="lwg-defects.html#38">38</a>.
</li>
<li>R10:
pre-Kona updated. Added proposed resolutions <a href="lwg-defects.html#83">83</a>,
<a href="lwg-defects.html#86">86</a>, <a href="lwg-active.html#91">91</a>, <a href="lwg-active.html#92">92</a>,
<a href="lwg-defects.html#109">109</a>. Added issues <a href="lwg-closed.html#190">190</a> to
<a href="lwg-defects.html#195">195</a>. (99-0033/D1209, 14 Oct 99)
</li>
<li>R9:
pre-Kona mailing. Added issues <a href="lwg-closed.html#140">140</a> to
<a href="lwg-defects.html#189">189</a>. Issues list split into separate &quot;active&quot; and
&quot;closed&quot; documents. (99-0030/N1206, 25 Aug 99)
</li>
<li>R8:
post-Dublin mailing. Updated to reflect LWG and full committee actions
in Dublin. (99-0016/N1193, 21 Apr 99)
</li>
<li>R7:
pre-Dublin updated: Added issues <a href="lwg-closed.html#130">130</a>, <a href="lwg-closed.html#131">131</a>,
<a href="lwg-defects.html#132">132</a>, <a href="lwg-defects.html#133">133</a>, <a href="lwg-defects.html#134">134</a>,
<a href="lwg-closed.html#135">135</a>, <a href="lwg-defects.html#136">136</a>, <a href="lwg-defects.html#137">137</a>,
<a href="lwg-closed.html#138">138</a>, <a href="lwg-defects.html#139">139</a> (31 Mar 99)
</li>
<li>R6:
pre-Dublin mailing. Added issues <a href="lwg-defects.html#127">127</a>, <a href="lwg-closed.html#128">128</a>,
and <a href="lwg-defects.html#129">129</a>. (99-0007/N1194, 22 Feb 99)
</li>
<li>R5:
update issues <a href="lwg-defects.html#103">103</a>, <a href="lwg-defects.html#112">112</a>; added issues
<a href="lwg-defects.html#114">114</a> to <a href="lwg-defects.html#126">126</a>. Format revisions to prepare
for making list public. (30 Dec 98)
</li>
<li>R4:
post-Santa Cruz II updated: Issues <a href="lwg-defects.html#110">110</a>,
<a href="lwg-closed.html#111">111</a>, <a href="lwg-defects.html#112">112</a>, <a href="lwg-closed.html#113">113</a> added, several
issues corrected. (22 Oct 98)
</li>
<li>R3:
post-Santa Cruz II: Issues <a href="lwg-closed.html#94">94</a> to <a href="lwg-defects.html#109">109</a>
added, many issues updated to reflect LWG consensus (12 Oct 98)
</li>
<li>R2:
pre-Santa Cruz II: Issues <a href="lwg-closed.html#73">73</a> to <a href="lwg-closed.html#93">93</a> added,
issue <a href="lwg-defects.html#17">17</a> updated. (29 Sep 98)
</li>
<li>R1:
Correction to issue <a href="lwg-defects.html#55">55</a> resolution, <a href="lwg-defects.html#60">60</a> code
format, <a href="lwg-defects.html#64">64</a> title. (17 Sep 98)
</li>
</ul>
<h2>
<a name="Status"></a>Issue Status</h2>
<p>
<b><a name="New">New</a></b> - The issue has not yet been
reviewed by the LWG. Any <b>Proposed Resolution</b> is purely a
suggestion from the issue submitter, and should not be construed as
the view of LWG.</p>
<p>
<b><a name="Open">Open</a></b> - The LWG has discussed the issue
but is not yet ready to move the issue forward. There are several
possible reasons for open status:</p>
<ul>
<li>Consensus may have not yet have been reached as to how to deal
with the issue.</li>
<li>Informal consensus may have been reached, but the LWG awaits
exact <b>Proposed Resolution</b> wording for review.</li>
<li>The LWG wishes to consult additional technical experts before
proceeding.</li>
<li>The issue may require further study.</li>
</ul>
<p>A <b>Proposed Resolution</b> for an open issue is still not be
construed as the view of LWG. Comments on the current state of
discussions are often given at the end of open issues in an italic
font. Such comments are for information only and should not be given
undue importance.</p>
<p>
<b><a name="Dup">Dup</a></b> - The LWG has reached consensus that
the issue is a duplicate of another issue, and will not be further
dealt with. A <b>Rationale</b> identities the duplicated issue's
issue number. </p>
<p>
<b><a name="NAD">NAD</a></b> - The LWG has reached consensus that
the issue is not a defect in the Standard, and the issue is ready to
forward to the full committee as a proposed record of response. A
<b>Rationale</b> discusses the LWG's reasoning.</p>
<p>
<b><a name="Review">Review</a></b> - Exact wording of a
<b>Proposed Resolution</b> is now available for review on an issue
for which the LWG previously reached informal consensus.</p>
<p>
<b><a name="Ready">Ready</a></b> - The LWG has reached consensus
that the issue is a defect in the Standard, the <b>Proposed
Resolution</b> is correct, and the issue is ready to forward to the
full committee for further action as a Defect Report (DR).</p>
<p>
<b><a name="DR">DR</a></b> - (Defect Report) - The full J16
committee has voted to forward the issue to the Project Editor to be
processed as a Potential Defect Report. The Project Editor reviews
the issue, and then forwards it to the WG21 Convenor, who returns it
to the full committee for final disposition. This issues list
accords the status of DR to all these Defect Reports regardless of
where they are in that process.</p>
<p>
<b><a name="TC">TC</a></b> - (Technical Corrigenda) - The full
WG21 committee has voted to accept the Defect Report's Proposed
Resolution as a Technical Corrigenda. Action on this issue is thus
complete and no further action is possible under ISO rules.</p>
<p>
<b><a name="RR">RR</a></b> - (Record of Response) - The full WG21
committee has determined that this issue is not a defect in the
Standard. Action on this issue is thus complete and no further
action is possible under ISO rules.</p>
<p>
<b><a name="Future">Future</a></b> - In addition to the regular
status, the LWG believes that this issue should be revisited at the
next revision of the standard. It is usually paired with NAD.</p>
<p>Issues are always given the status of <a href="lwg-active.html#New">New</a> when
they first appear on the issues list. They may progress to
<a href="lwg-active.html#Open">Open</a> or <a href="lwg-active.html#Review">Review</a> while the LWG
is actively working on them. When the LWG has reached consensus on
the disposition of an issue, the status will then change to
<a href="lwg-active.html#Dup">Dup</a>, <a href="lwg-active.html#NAD">NAD</a>, or <a href="lwg-active.html#Ready">Ready</a> as appropriate. Once the full J16 committee votes to
forward Ready issues to the Project Editor, they are given the
status of Defect Report ( <a href="lwg-active.html#DR">DR</a>). These in turn may
become the basis for Technical Corrigenda (<a href="lwg-active.html#TC">TC</a>),
or are closed without action other than a Record of Response
(<a href="lwg-active.html#RR">RR</a> ). The intent of this LWG process is that
only issues which are truly defects in the Standard move to the
formal ISO DR status.
</p>
<h2>Active Issues</h2>
<hr>
<a name="23"><h3>23.&nbsp;Num_get overflow result</h3></a><p>
<b>Section:</b>&nbsp;22.2.2.1.2 <a href="lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Nathan Myers&nbsp; <b>Date:</b>&nbsp;6 Aug 1998</p>
<p>The current description of numeric input does not account for the possibility of
overflow. This is an implicit result of changing the description to rely on the definition
of scanf() (which fails to report overflow), and conflicts with the documented behavior of
traditional and current implementations. </p>
<p>Users expect, when reading a character sequence that results in a value unrepresentable
in the specified type, to have an error reported. The standard as written does not permit
this. </p>
<p><b>Further comments from Dietmar:</b></p>
<p>
I don't feel comfortable with the proposed resolution to issue 23: It
kind of simplifies the issue to much. Here is what is going on:
</p>
<p>
Currently, the behavior of numeric overflow is rather counter intuitive
and hard to trace, so I will describe it briefly:
</p>
<ul>
<li>
According to 22.2.2.1.2 <a href="lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>
paragraph 11 <tt>failbit</tt> is set if <tt>scanf()</tt> would
return an input error; otherwise a value is converted to the rules
of <tt>scanf</tt>.
</li>
<li>
<tt>scanf()</tt> is defined in terms of <tt>fscanf()</tt>.
</li>
<li>
<tt>fscanf()</tt> returns an input failure if during conversion no
character matching the conversion specification could be extracted
before reaching EOF. This is the only reason for <tt>fscanf()</tt>
to fail due to an input error and clearly does not apply to the case
of overflow.
</li>
<li>
Thus, the conversion is performed according to the rules of
<tt>fscanf()</tt> which basically says that <tt>strtod</tt>,
<tt>strtol()</tt>, etc. are to be used for the conversion.
</li>
<li>
The <tt>strtod()</tt>, <tt>strtol()</tt>, etc. functions consume as
many matching characters as there are and on overflow continue to
consume matching characters but also return a value identical to
the maximum (or minimum for signed types if there was a leading minus)
value of the corresponding type and set <tt>errno</tt> to <tt>ERANGE</tt>.
</li>
<li>
Thus, according to the current wording in the standard, overflows
can be detected! All what is to be done is to check <tt>errno</tt>
after reading an element and, of course, clearing <tt>errno</tt>
before trying a conversion. With the current wording, it can be
detected whether the overflow was due to a positive or negative
number for signed types.
</li>
</ul>
<p><b>Further discussion from Redmond:</b></p>
<p>The basic problem is that we've defined our behavior,
including our error-reporting behavior, in terms of C90. However,
C90's method of reporting overflow in scanf is not technically an
&quot;input error&quot;. The <tt>strto_*</tt> functions are more precise.</p>
<p>There was general consensus that <tt>failbit</tt> should be set
upon overflow. We considered three options based on this:</p>
<ol>
<li>Set failbit upon conversion error (including overflow), and
don't store any value.</li>
<li>Set failbit upon conversion error, and also set <tt>errno</tt> to
indicated the precise nature of the error.</li>
<li>Set failbit upon conversion error. If the error was due to
overflow, store +-numeric_limits&lt;T&gt;::max() as an
overflow indication.</li>
</ol>
<p>Straw poll: (1) 5; (2) 0; (3) 8.</p>
<p>PJP will provide wording.</p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="44"><h3>44.&nbsp;Iostreams use operator== on int_type values</h3></a><p>
<b>Section:</b>&nbsp;27 <a href="lib-iostreams.html#lib.input.output"> [lib.input.output]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Nathan Myers&nbsp; <b>Date:</b>&nbsp;6 Aug 1998</p>
<p>Many of the specifications for iostreams specify that character
values or their int_type equivalents are compared using operators ==
or !=, though in other places traits::eq() or traits::eq_int_type is
specified to be used throughout. This is an inconsistency; we should
change uses of == and != to use the traits members instead. </p>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: Nathan to supply proposed wording]</i></p>
<p><i>[
Tokyo: the LWG reaffirmed that this is a defect, and requires careful
review of clause 27 as the changes are context sensitive.
]</i></p>
<hr>
<a name="76"><h3>76.&nbsp;Can a <tt>codecvt</tt> facet always convert one internal character at a time?</h3></a><p>
<b>Section:</b>&nbsp;22.2.1.5 <a href="lib-locales.html#lib.locale.codecvt"> [lib.locale.codecvt]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;25 Sep 1998</p>
<p>This issue concerns the requirements on classes derived from
<tt>codecvt</tt>, including user-defined classes. What are the
restrictions on the conversion from external characters
(e.g. <tt>char</tt>) to internal characters (e.g. <tt>wchar_t</tt>)?
Or, alternatively, what assumptions about <tt>codecvt</tt> facets can
the I/O library make? </p>
<p>The question is whether it's possible to convert from internal
characters to external characters one internal character at a time,
and whether, given a valid sequence of external characters, it's
possible to pick off internal characters one at a time. Or, to put it
differently: given a sequence of external characters and the
corresponding sequence of internal characters, does a position in the
internal sequence correspond to some position in the external
sequence? </p>
<p>To make this concrete, suppose that <tt>[first, last)</tt> is a
sequence of <i>M</i> external characters and that <tt>[ifirst,
ilast)</tt> is the corresponding sequence of <i>N</i> internal
characters, where <i>N &gt; 1</i>. That is, <tt>my_encoding.in()</tt>,
applied to <tt>[first, last)</tt>, yields <tt>[ifirst,
ilast)</tt>. Now the question: does there necessarily exist a
subsequence of external characters, <tt>[first, last_1)</tt>, such
that the corresponding sequence of internal characters is the single
character <tt>*ifirst</tt>?
</p>
<p>(What a &quot;no&quot; answer would mean is that
<tt>my_encoding</tt> translates sequences only as blocks. There's a
sequence of <i>M</i> external characters that maps to a sequence of
<i>N</i> internal characters, but that external sequence has no
subsequence that maps to <i>N-1</i> internal characters.) </p>
<p>Some of the wording in the standard, such as the description of
<tt>codecvt::do_max_length</tt> (22.2.1.5.2 <a href="lib-locales.html#lib.locale.codecvt.virtuals"> [lib.locale.codecvt.virtuals]</a>,
paragraph 11) and <tt>basic_filebuf::underflow</tt> (27.8.1.4 <a href="lib-iostreams.html#lib.filebuf.virtuals"> [lib.filebuf.virtuals]</a>, paragraph 3) suggests that it must always be
possible to pick off internal characters one at a time from a sequence
of external characters. However, this is never explicitly stated one
way or the other. </p>
<p>This issue seems (and is) quite technical, but it is important if
we expect users to provide their own encoding facets. This is an area
where the standard library calls user-supplied code, so a well-defined
set of requirements for the user-supplied code is crucial. Users must
be aware of the assumptions that the library makes. This issue affects
positioning operations on <tt>basic_filebuf</tt>, unbuffered input,
and several of <tt>codecvt</tt>'s member functions. </p>
<p><b>Proposed resolution:</b></p>
<p>Add the following text as a new paragraph, following 22.2.1.5.2 <a href="lib-locales.html#lib.locale.codecvt.virtuals"> [lib.locale.codecvt.virtuals]</a> paragraph 2:</p>
<blockquote>
<p>A <tt>codecvt</tt> facet that is used by <tt>basic_filebuf</tt>
(27.8 <a href="lib-iostreams.html#lib.file.streams"> [lib.file.streams]</a>) must have the property that if</p>
<pre>
do_out(state, from, from_end, from_next, to, to_lim, to_next)
</pre>
would return <tt>ok</tt>, where <tt>from != from_end</tt>, then
<pre>
do_out(state, from, from + 1, from_next, to, to_end, to_next)
</pre>
must also return <tt>ok</tt>, and that if
<pre>
do_in(state, from, from_end, from_next, to, to_lim, to_next)
</pre>
would return <tt>ok</tt>, where <tt>to != to_lim</tt>, then
<pre>
do_in(state, from, from_end, from_next, to, to + 1, to_next)
</pre>
<p>must also return <tt>ok</tt>. [<i>Footnote:</i> Informally, this
means that <tt>basic_filebuf</tt> assumes that the mapping from
internal to external characters is 1 to N: a <tt>codecvt</tt> that is
used by <tt>basic_filebuf</tt> must be able to translate characters
one internal character at a time. <i>--End Footnote</i>]</p>
</blockquote>
<p><i>[Redmond: Minor change in proposed resolution. Original
proposed resolution talked about &quot;success&quot;, with a parenthetical
comment that success meant returning <tt>ok</tt>. New wording
removes all talk about &quot;success&quot;, and just talks about the
return value.]</i></p>
<p><b>Rationale:</b></p>
<p>The proposed resoluion says that conversions can be performed one
internal character at a time. This rules out some encodings that
would otherwise be legal. The alternative answer would mean there
would be some internal positions that do not correspond to any
external file position.</p>
<p>
An example of an encoding that this rules out is one where the
<tt>internT</tt> and <tt>externT</tt> are of the same type, and
where the internal sequence <tt>c1 c2</tt> corresponds to the
external sequence <tt>c2 c1</tt>.
</p>
<p>It was generally agreed that <tt>basic_filebuf</tt> relies
on this property: it was designed under the assumption that
the external-to-internal mapping is N-to-1, and it is not clear
that <tt>basic_filebuf</tt> is implementable without that
restriction.
</p>
<p>
The proposed resolution is expressed as a restriction on
<tt>codecvt</tt> when used by <tt>basic_filebuf</tt>, rather
than a blanket restriction on all <tt>codecvt</tt> facets,
because <tt>basic_filebuf</tt> is the only other part of the
library that uses <tt>codecvt</tt>. If a user wants to define
a <tt>codecvt</tt> facet that implements a more general N-to-M
mapping, there is no reason to prohibit it, so long as the user
does not expect <tt>basic_filebuf</tt> to be able to use it.
</p>
<hr>
<a name="91"><h3>91.&nbsp;Description of operator&gt;&gt; and getline() for string&lt;&gt; might cause endless loop</h3></a><p>
<b>Section:</b>&nbsp;21.3.7.9 <a href="lib-strings.html#lib.string.io"> [lib.string.io]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Nico Josuttis&nbsp; <b>Date:</b>&nbsp;29 Sep 1998</p>
<p>Operator &gt;&gt; and getline() for strings read until eof()
in the input stream is true. However, this might never happen, if the
stream can't read anymore without reaching EOF. So shouldn't it be
changed into that it reads until !good() ? </p>
<p><b>Proposed resolution:</b></p>
<p>In 21.3.7.9 <a href="lib-strings.html#lib.string.io"> [lib.string.io]</a>, paragraph 1, replace:</p>
<blockquote>
Effects: Begins by constructing a sentry object k as if k were
constructed by typename basic_istream&lt;charT,traits&gt;::sentry k( is). If
bool( k) is true, it calls str.erase() and then extracts characters
from is and appends them to str as if by calling str.append(1, c). If
is.width() is greater than zero, the maximum number n of characters
appended is is.width(); otherwise n is str.max_size(). Characters are
extracted and appended until any of the following occurs:
</blockquote>
<p>with:</p>
<blockquote>
Effects: Behaves as a formatted input function (27.6.1.2.1 <a href="lib-iostreams.html#lib.istream.formatted.reqmts"> [lib.istream.formatted.reqmts]</a>). After constructing a sentry object, if the
sentry converts to true, calls str.erase() and then extracts
characters from is and appends them to str as if by calling
str.append(1,c). If is.width() is greater than zero, the maximum
number n of characters appended is is.width(); otherwise n is
str.max_size(). Characters are extracted and appended until any of the
following occurs:
</blockquote>
<p>In 21.3.7.9 <a href="lib-strings.html#lib.string.io"> [lib.string.io]</a>, paragraph 6, replace</p>
<blockquote>
Effects: Begins by constructing a sentry object k as if by typename
basic_istream&lt;charT,traits&gt;::sentry k( is, true). If bool( k) is true,
it calls str.erase() and then extracts characters from is and appends
them to str as if by calling str.append(1, c) until any of the
following occurs:
</blockquote>
<p>with:</p>
<blockquote>
Effects: Behaves as an unformatted input function (27.6.1.3 <a href="lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a>), except that it does not affect the value returned
by subsequent calls to basic_istream&lt;&gt;::gcount(). After
constructing a sentry object, if the sentry converts to true, calls
str.erase() and then extracts characters from is and appends them to
str as if by calling str.append(1,c) until any of the following
occurs:
</blockquote>
<p><i>[Redmond: Made changes in proposed resolution. <tt>operator&gt;&gt;</tt>
should be a formatted input function, not an unformatted input function.
<tt>getline</tt> should not be required to set <tt>gcount</tt>, since
there is no mechanism for <tt>gcount</tt> to be set except by one of
<tt>basic_istream</tt>'s member functions.]</i></p>
<p><b>Rationale:</b></p>
<p>The real issue here is whether or not these string input functions
get their characters from a streambuf, rather than by calling an
istream's member functions, a streambuf signals failure either by
returning eof or by throwing an exception; there are no other
possibilities. The proposed resolution makes it clear that these two
functions do get characters from a streambuf.</p>
<hr>
<a name="92"><h3>92.&nbsp;Incomplete Algorithm Requirements</h3></a><p>
<b>Section:</b>&nbsp;25 <a href="lib-algorithms.html#lib.algorithms"> [lib.algorithms]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Nico Josuttis&nbsp; <b>Date:</b>&nbsp;29 Sep 1998</p>
<p>The standard does not state, how often a function object is copied,
called, or the order of calls inside an algorithm. This may lead to
surprising/buggy behavior. Consider the following example: </p>
<pre>class Nth { // function object that returns true for the nth element
private:
int nth; // element to return true for
int count; // element counter
public:
Nth (int n) : nth(n), count(0) {
}
bool operator() (int) {
return ++count == nth;
}
};
....
// remove third element
list&lt;int&gt;::iterator pos;
pos = remove_if(coll.begin(),coll.end(), // range
Nth(3)), // remove criterion
coll.erase(pos,coll.end()); </pre>
<p>This call, in fact removes the 3rd <b>AND the 6th</b> element. This
happens because the usual implementation of the algorithm copies the
function object internally: </p>
<pre>template &lt;class ForwIter, class Predicate&gt;
ForwIter std::remove_if(ForwIter beg, ForwIter end, Predicate op)
{
beg = find_if(beg, end, op);
if (beg == end) {
return beg;
}
else {
ForwIter next = beg;
return remove_copy_if(++next, end, beg, op);
}
} </pre>
<p>The algorithm uses find_if() to find the first element that should
be removed. However, it then uses a copy of the passed function object
to process the resulting elements (if any). Here, Nth is used again
and removes also the sixth element. This behavior compromises the
advantage of function objects being able to have a state. Without any
cost it could be avoided (just implement it directly instead of
calling find_if()). </p>
<p><b>Proposed resolution:</b></p>
<p> In [lib.function.objects] 20.3 Function objects add as new
paragraph 6 (or insert after paragraph 1): </p>
<p>Option 1: </p>
<blockquote>
Predicates are functions or function objects that fulfill the
following requirements:<br> &nbsp; - They return a Boolean value (bool
or a value convertible to bool)<br> &nbsp; - It doesn't matter for the
behavior of a predicate how often it is copied or assigned and how
often it is called.
</blockquote>
<p>Option 2: </p>
<blockquote>
- if it's a function:<br> &nbsp; - All calls with the same
argument values yield the same result.<br> - if it's a function
object:<br> &nbsp; - In any sequence of calls to operator () without
calling any non-constant member function, all calls with the same
argument values yield the same result.&nbsp;<br> - After an assignment
or copy both objects return the same result for the same values.
</blockquote>
<p><i>[Santa Cruz: The LWG believes that there may be more to this than
meets the eye. It applies to all function objects, particularly
predicates. Two questions: (1) must a function object be
copyable? (2) how many times is a function object called?&nbsp; These
are in effect questions about state.&nbsp; Function objects appear to
require special copy semantics to make state work, and may fail if
calling alters state and calling occurs an unexpected number of
times.]</i></p>
<p><i>[Dublin: Pete Becker felt that this may not be a defect,
but rather something that programmers need to be educated about.
There was discussion of adding wording to the effect that the number
and order of calls to function objects, including predicates, not
affect the behavior of the function object.]</i></p>
<p><i>[Pre-Kona: Nico comments: It seems the problem is that we don't
have a clear statement of &quot;predicate&quot; in the
standard. People including me seemed to think &quot;a function
returning a Boolean value and being able to be called by an STL
algorithm or be used as sorting criterion or ... is a
predicate&quot;. But a predicate has more requirements: It should
never change its behavior due to a call or being copied. IMHO we have
to state this in the standard. If you like, see section 8.1.4 of my
library book for a detailed discussion.]</i></p>
<p><i>[Kona: Nico will provide wording to the effect that &quot;unless
otherwise specified, the number of copies of and calls to function
objects by algorithms is unspecified&quot;.&nbsp; Consider placing in
25 <a href="lib-algorithms.html#lib.algorithms"> [lib.algorithms]</a> after paragraph 9.]</i></p>
<p><i>[Pre-Tokyo: Angelika Langer comments: if the resolution is
that algorithms are free to copy and pass around any function objects,
then it is a valid question whether they are also allowed to change
the type information from reference type to value type.]</i></p>
<p><i>[Tokyo: Nico will discuss this further with Matt as there are
multiple problems beyond the underlying problem of no definition of
&quot;Predicate&quot;.]</i></p>
<p><i>[Post-Tokyo: Nico provided the above proposed
resolutions.]</i></p>
<hr>
<a name="96"><h3>96.&nbsp;Vector&lt;bool&gt; is not a container</h3></a><p>
<b>Section:</b>&nbsp;23.2.5 <a href="lib-containers.html#lib.vector.bool"> [lib.vector.bool]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;AFNOR&nbsp; <b>Date:</b>&nbsp;7 Oct 1998</p>
<p>
<tt>vector&lt;bool&gt;</tt> is not a container as its reference and
pointer types are not references and pointers. </p>
<p>Also it forces everyone to have a space optimization instead of a
speed one.</p>
<p>
<b>See also:</b> 99-0008 == N1185 Vector&lt;bool&gt; is
Nonconforming, Forces Optimization Choice.</p>
<p><b>Proposed resolution:</b></p>
<p><i>[In Santa Cruz the LWG felt that this was Not A Defect.]</i></p>
<p><i>[In Dublin many present felt that failure to meet Container
requirements was a defect. There was disagreement as to whether
or not the optimization requirements constituted a defect.]</i></p>
<p><i>[The LWG looked at the following resolutions in some detail:
<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Not A Defect.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Add a note explaining that vector&lt;bool&gt; does not meet
Container requirements.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Remove vector&lt;bool&gt;.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Add a new category of container requirements which
vector&lt;bool&gt; would meet.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Rename vector&lt;bool&gt;.<br>
<br>
No alternative had strong, wide-spread, support and every alternative
had at least one &quot;over my dead body&quot; response.<br>
<br>
There was also mention of a transition scheme something like (1) add
vector_bool and deprecate vector&lt;bool&gt; in the next standard. (2)
Remove vector&lt;bool&gt; in the following standard.]</i></p>
<p><i>[Modifying container requirements to permit returning proxies
(thus allowing container requirements conforming vector&lt;bool&gt;)
was also discussed.]</i></p>
<p><i>[It was also noted that there is a partial but ugly workaround in
that vector&lt;bool&gt; may be further specialized with a customer
allocator.]</i></p>
<p><i>[Kona: Herb Sutter presented his paper J16/99-0035==WG21/N1211,
vector&lt;bool&gt;: More Problems, Better Solutions. Much discussion
of a two step approach: a) deprecate, b) provide replacement under a
new name. LWG straw vote on that: 1-favor, 11-could live with, 2-over
my dead body. This resolution was mentioned in the LWG report to the
full committee, where several additional committee members indicated
over-my-dead-body positions.]</i></p>
<p><i>[Tokyo: Not discussed by the full LWG; no one claimed new
insights and so time was more productively spent on other issues. In
private discussions it was asserted that requirements for any solution
include 1) Increasing the full committee's understanding of the
problem, and 2) providing compiler vendors, authors, teachers, and of
course users with specific suggestions as to how to apply the eventual
solution.]</i></p>
<hr>
<a name="98"><h3>98.&nbsp;Input iterator requirements are badly written</h3></a><p>
<b>Section:</b>&nbsp;24.1.1 <a href="lib-iterators.html#lib.input.iterators"> [lib.input.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;AFNOR&nbsp; <b>Date:</b>&nbsp;7 Oct 1998</p>
<p>Table 72 in 24.1.1 <a href="lib-iterators.html#lib.input.iterators"> [lib.input.iterators]</a> specifies semantics for
<tt>*r++</tt> of:</p>
<p>&nbsp;&nbsp; <tt>{ T tmp = *r; ++r; return tmp; }</tt>
</p>
<p>There are two problems with this. First, the return type is
specified to be &quot;T&quot;, as opposed to something like &quot;convertible to T&quot;.
This is too specific: we want to allow *r++ to return an lvalue.</p>
<p>Second, writing the semantics in terms of code misleadingly
suggests that the effects *r++ should precisely replicate the behavior
of this code, including side effects. (What if it's a user-defined
type whose copy constructor has observable behavior?) We should
replace the code with words, or else put some blanket statement in
clause 17 saying that code samples aren't intended to specify exactly
how many times a copy constructor is called, even if the copy
constructor has observable behavior. (See issue <a href="lwg-active.html#334">334</a>
for a similar problem.)</p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="120"><h3>120.&nbsp;Can an implementor add specializations?</h3></a><p>
<b>Section:</b>&nbsp;17.4.3.1 <a href="lib-intro.html#lib.reserved.names"> [lib.reserved.names]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Judy Ward&nbsp; <b>Date:</b>&nbsp;15 Dec 1998</p>
<p>The original issue asked whether a library implementor could
specialize standard library templates for built-in types. (This was
an issue because users are permitted to explicitly instantiate
standard library templates.)</p>
<p>Specializations are no longer a problem, because of the resolution
to core issue 259. Under the proposed resolution, it will be legal
for a translation unit to contain both a specialization and an
explicit instantiation of the same template, provided that the
specialization comes first. In such a case, the explicit
instantiation will be ignored. Further discussion of library issue
120 assumes that the core 259 resolution will be adopted.</p>
<p>However, as noted in lib-7047, one piece of this issue still
remains: what happens if a standard library implementor explicitly
instantiates a standard library templates? It's illegal for a program
to contain two different explicit instantiations of the same template
for the same type in two different translation units (ODR violation),
and the core working group doesn't believe it is practical to relax
that restriction.</p>
<p>The issue, then, is: are users allowed to implicitly instantiate
standard library templates for non-user defined types? The status quo
answer is 'yes'. Changing it to 'no' would give library implementors
more freedom.</p>
<p>This is an issue because, for performance reasons, library
implementors often need to explicitly instantiate standard library
templates. (for example, std::basic_string&lt;char&gt;) Does giving
users freedom to explicitly instantiate standard library templates for
non-user defined types make it impossible or painfully difficult for
library implementors to do this?</p>
<p>John Spicer suggests, in lib-8957, that library implementors have a
mechanism they can use for explicit instantiations that doesn't
prevent users from performing their own explicit instantiations: put
each explicit instantiation in its own object file. (Different
solutions might be necessary for Unix DSOs or MS-Windows DLLs.) On
some platforms, library implementors might not need to do anything
special: the &quot;undefined behavior&quot; that results from having two
different explicit instantiations might be harmless.</p>
<p><b>Proposed resolution:</b></p>
<p>Option 1.</p>
<blockquote>
<p>Append to 17.4.3.1 <a href="lib-intro.html#lib.reserved.names"> [lib.reserved.names]</a> paragraph 1: </p>
<blockquote>
A program may explicitly instantiate any templates in the standard
library only if the declaration depends on a user-defined name of
external linkage and the instantiation meets the standard library
requirements for the original template.
</blockquote>
</blockquote>
<p>Option 2.</p>
<blockquote>
<p>In light of the resolution to core issue 259, no normative changes
in the library clauses are necessary. Add the following non-normative
note to the end of 17.4.3.1 <a href="lib-intro.html#lib.reserved.names"> [lib.reserved.names]</a> paragraph 1:</p>
<blockquote>
[<i>Note:</i> A program may explicitly instantiate standard library
templates, even when an explicit instantiation does not depend on
a user-defined name. <i>--end note</i>]
</blockquote>
</blockquote>
<p><i>[Copenhagen: LWG discussed three options. (A) Users may not
explicitly instantiate standard library templates, except on
user-defined types. Consequence: library implementors may freely
specialize or instantiate templates. (B) It is implementation defined
whether users may explicitly instantiate standard library templates on
non-user-defined types. Consequence: library implementors may freely
specialize or instantiate templates, but may need to document some or
all templates that have been explicitly instantiated. (C) Users may
explicitly instantiate any standard library template.
]</i></p>
<p><i>[Straw poll (first number is favor, second is strongly oppose):
A - 4, 0; B - 0, 9; C - 9, 1. Proposed resolution 1, above, is
option A. (It is the original proposed resolution.) Proposed
resolution 2, above, is option C. Because there was no support
for option B, no wording is provided.]</i></p>
<p><i>[Redmond: discussed again; straw poll had results similar to
those of Copenhagen (A - 1, 3; B - 6, 2; C - 8, 4). Most people said
they could live with any option. The only objection to option A is
potential implementation difficulty. Steve Clamage volunteered do a
survey to see if there are any popular platforms where option A would
present a real problem for implementors. See his reflector message,
c++std-lib-9002.
]</i></p>
<hr>
<a name="123"><h3>123.&nbsp;Should valarray helper arrays fill functions be const?</h3></a><p>
<b>Section:</b>&nbsp;26.3.5.4 <a href="lib-numerics.html#lib.slice.arr.fill"> [lib.slice.arr.fill]</a>, 26.3.7.4 <a href="lib-numerics.html#lib.gslice.array.fill"> [lib.gslice.array.fill]</a>, 26.3.8.4 <a href="lib-numerics.html#lib.mask.array.fill"> [lib.mask.array.fill]</a>, 26.3.9.4 <a href="lib-numerics.html#lib.indirect.array.fill"> [lib.indirect.array.fill]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Judy Ward&nbsp; <b>Date:</b>&nbsp;15 Dec 1998 </p>
<p>One of the operator= in the valarray helper arrays is const and one
is not. For example, look at slice_array. This operator= in Section
26.3.5.2 <a href="lib-numerics.html#lib.slice.arr.assign"> [lib.slice.arr.assign]</a> is const: </p>
<p>&nbsp;&nbsp;&nbsp; <tt>void operator=(const valarray&lt;T&gt;&amp;) const;</tt> </p>
<p>but this one in Section 26.3.5.4 <a href="lib-numerics.html#lib.slice.arr.fill"> [lib.slice.arr.fill]</a> is not: </p>
<p>&nbsp;&nbsp;&nbsp; <tt>void operator=(const T&amp;); </tt>
</p>
<p>The description of the semantics for these two functions is similar. </p>
<p><b>Proposed resolution:</b></p>
<p>26.3.5 <a href="lib-numerics.html#lib.template.slice.array"> [lib.template.slice.array]</a> Template class slice_array</p>
<blockquote>
<p>In the class template definition for slice_array, replace the member
function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>with</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p>26.3.5.4 <a href="lib-numerics.html#lib.slice.arr.fill"> [lib.slice.arr.fill]</a> slice_array fill function</p>
<blockquote>
<p>Change the function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>to</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p>26.3.7 <a href="lib-numerics.html#lib.template.gslice.array"> [lib.template.gslice.array]</a> Template class gslice_array</p>
<blockquote>
<p>In the class template definition for gslice_array, replace the member
function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>with</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p>26.3.7.4 <a href="lib-numerics.html#lib.gslice.array.fill"> [lib.gslice.array.fill]</a> gslice_array fill function</p>
<blockquote>
<p>Change the function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>to</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p>26.3.8 <a href="lib-numerics.html#lib.template.mask.array"> [lib.template.mask.array]</a> Template class mask_array</p>
<blockquote>
<p>In the class template definition for mask_array, replace the member
function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>with</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p>26.3.8.4 <a href="lib-numerics.html#lib.mask.array.fill"> [lib.mask.array.fill]</a> mask_array fill function</p>
<blockquote>
<p>Change the function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>to</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p>26.3.9 <a href="lib-numerics.html#lib.template.indirect.array"> [lib.template.indirect.array]</a> Template class indirect_array</p>
<blockquote>
<p>In the class template definition for indirect_array, replace the member
function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>with</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p>26.3.9.4 <a href="lib-numerics.html#lib.indirect.array.fill"> [lib.indirect.array.fill]</a> indirect_array fill function</p>
<blockquote>
<p>Change the function declaration</p>
<pre>
void operator=(const T&amp;);
</pre>
<p>to</p>
<pre>
void operator=(const T&amp;) const;
</pre>
</blockquote>
<p><i>[Redmond: Robert provided wording.]</i></p>
<p><b>Rationale:</b></p>
<p>There's no good reason for one version of operator= being const and
another one not. Because of issue <a href="lwg-active.html#253">253</a>, this now
matters: these functions are now callable in more circumstances. In
many existing implementations, both versions are already const.</p>
<hr>
<a name="167"><h3>167.&nbsp;Improper use of <tt>traits_type::length()</tt>
</h3></a><p>
<b>Section:</b>&nbsp;27.6.2.5.4 <a href="lib-iostreams.html#lib.ostream.inserters.character"> [lib.ostream.inserters.character]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Dietmar K&uuml;hl&nbsp; <b>Date:</b>&nbsp;20 Jul 1999</p>
<p>Paragraph 4 states that the length is determined using
<tt>traits::length(s)</tt>. Unfortunately, this function is not
defined for example if the character type is <tt>wchar_t</tt> and the
type of <tt>s</tt> is <tt>char const*</tt>. Similar problems exist if
the character type is <tt>char</tt> and the type of <tt>s</tt> is
either <tt>signed char const*</tt> or <tt>unsigned char
const*</tt>.</p>
<p><b>Proposed resolution:</b></p>
<p>Change 27.6.2.5.4 <a href="lib-iostreams.html#lib.ostream.inserters.character"> [lib.ostream.inserters.character]</a> paragraph 4 from:</p>
<blockquote>
<p>Effects: Behaves like an formatted inserter (as described in
lib.ostream.formatted.reqmts) of out. After a sentry object is
constructed it inserts characters. The number of characters starting
at s to be inserted is traits::length(s). Padding is determined as
described in lib.facet.num.put.virtuals. The traits::length(s)
characters starting at s are widened using out.widen
(lib.basic.ios.members). The widened characters and any required
padding are inserted into out. Calls width(0).</p>
</blockquote>
<p>to:</p>
<blockquote>
<p>Effects: Behaves like an formatted inserter (as described in
lib.ostream.formatted.reqmts) of out. After a sentry object is
constructed it inserts characters. The number len of characters
starting at s to be inserted is</p>
<p>
- traits::length((const char*)s) if the second argument is of type
const charT*<br>
- char_traits&lt;char&gt;::length(s) if the second argument is of
type const char*, const signed char*, or const unsigned char* and
and charT is not char.<br>
</p>
<p>Padding is determined as described in
lib.facet.num.put.virtuals. The len characters starting at s are
widened using out.widen (lib.basic.ios.members). The widened
characters and any required padding are inserted into out. Calls
width(0).</p>
</blockquote>
<p><i>[Kona: It is clear to the LWG there is a defect here.
Dietmar will supply specific wording.]</i></p>
<p><i>[Post-Tokyo: Dietmar supplied the above wording.]</i></p>
<p><i>[Toronto: The original proposed resolution involved
char_traits&lt;signed char&gt; and char_traits&lt;unsigned char&gt;.
There was strong opposition to requiring that library implementors
provide those specializations of char_traits.]</i></p>
<p><i>[Copenhagen: This still isn't quite right: proposed resolution
text got garbled when the signed char/unsigned char specializations
were removed. Dietmar will provide revised wording.]</i></p>
<hr>
<a name="179"><h3>179.&nbsp;Comparison of const_iterators to iterators doesn't work</h3></a><p>
<b>Section:</b>&nbsp;23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Judy Ward&nbsp; <b>Date:</b>&nbsp;2 Jul 1998</p>
<p>Currently the following will not compile on two well-known standard
library implementations:</p>
<blockquote>
<pre>#include &lt;set&gt;
using namespace std;
void f(const set&lt;int&gt; &amp;s)
{
set&lt;int&gt;::iterator i;
if (i==s.end()); // s.end() returns a const_iterator
}</pre>
</blockquote>
<p>
The reason this doesn't compile is because operator== was implemented
as a member function of the nested classes set:iterator and
set::const_iterator, and there is no conversion from const_iterator to
iterator. Surprisingly, (s.end() == i) does work, though, because of
the conversion from iterator to const_iterator.
</p>
<p>
I don't see a requirement anywhere in the standard that this must
work. Should there be one? If so, I think the requirement would need
to be added to the tables in section 24.1.1. I'm not sure about the
wording. If this requirement existed in the standard, I would think
that implementors would have to make the comparison operators
non-member functions.</p>
<p>This issues was also raised on comp.std.c++ by Darin
Adler.&nbsp; The example given was:</p>
<blockquote>
<pre>bool check_equal(std::deque&lt;int&gt;::iterator i,
std::deque&lt;int&gt;::const_iterator ci)
{
return i == ci;
}</pre>
</blockquote>
<p>Comment from John Potter:</p>
<blockquote>
<p>
In case nobody has noticed, accepting it will break reverse_iterator.
</p>
<p>
The fix is to make the comparison operators templated on two types.
</p>
<pre>
template &lt;class Iterator1, class Iterator2&gt;
bool operator== (reverse_iterator&lt;Iterator1&gt; const&amp; x,
reverse_iterator&lt;Iterator2&gt; const&amp; y);
</pre>
<p>
Obviously: return x.base() == y.base();
</p>
<p>
Currently, no reverse_iterator to const_reverse_iterator compares are
valid.
</p>
<p>
BTW, I think the issue is in support of bad code. Compares should be
between two iterators of the same type. All std::algorithms require
the begin and end iterators to be of the same type.
</p>
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>Insert this paragraph after 23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a> paragraph 7:</p>
<blockquote>
<p>In the expressions</p>
<pre>
i == j
i != j
i &lt; j
i &lt;= j
i &gt;= j
i &gt; j
i - j
</pre>
<p>Where i and j denote objects of a container's iterator type,
either or both may be replaced by an object of the container's
const_iterator type referring to the same element with no
change in semantics.</p>
</blockquote>
<p><i>[post-Toronto: Judy supplied a proposed resolution saying that
<tt>iterator</tt> and <tt>const_iterator</tt> could be freely mixed in
iterator comparison and difference operations.]</i></p>
<p><i>[Redmond: Dave and Howard supplied a new proposed resolution which
explicitly listed expressions; there was concern that the previous
proposed resolution was too informal.]</i></p>
<p><b>Rationale:</b></p>
<p>
The LWG believes it is clear that the above wording applies only to
the nested types <tt>X::iterator</tt> and <tt>X::const_iterator</tt>,
where <tt>X</tt> is a container. There is no requirement that
<tt>X::reverse_iterator</tt> and <tt>X::const_reverse_iterator</tt>
can be mixed. If mixing them is considered important, that's a
separate issue. (Issue <a href="lwg-active.html#280">280</a>.)
</p>
<hr>
<a name="187"><h3>187.&nbsp;iter_swap underspecified</h3></a><p>
<b>Section:</b>&nbsp;25.2.2 <a href="lib-algorithms.html#lib.alg.swap"> [lib.alg.swap]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Andrew Koenig&nbsp; <b>Date:</b>&nbsp;14 Aug 1999</p>
<p>The description of iter_swap in 25.2.2 paragraph 7,says that it ``exchanges the values''
of the objects to which two iterators refer.<br>
<br>
What it doesn't say is whether it does so using swap or using the assignment operator and copy constructor.<br>
<br>
This question is an important one to answer, because swap is specialized to work efficiently for standard containers.<br>
For example:</p>
<blockquote>
<pre>vector&lt;int&gt; v1, v2;
iter_swap(&amp;v1, &amp;v2);</pre>
</blockquote>
<p>Is this call to iter_swap equivalent to calling swap(v1, v2)?&nbsp; Or is it equivalent to</p>
<blockquote>
<pre>{
vector&lt;int&gt; temp = v1;
v1 = v2;
v2 = temp;
}</pre>
</blockquote>
<p>The first alternative is O(1); the second is O(n).</p>
<p>A LWG member, Dave Abrahams, comments:</p>
<blockquote>
<p>Not an objection necessarily, but I want to point out the cost of that requirement:</p>
<blockquote>
<p><tt>iter_swap(list&lt;T&gt;::iterator, list&lt;T&gt;::iterator)</tt></p>
</blockquote>
<p>can currently be specialized to be more efficient than iter_swap(T*,T*) for many T (by using splicing). Your proposal would make that optimization
illegal.&nbsp;</p>
</blockquote>
<p><i>[Kona: The LWG notes the original need for iter_swap was proxy iterators
which are no longer permitted.]</i></p>
<p><b>Proposed resolution:</b></p>
<p>Change the effect clause of iter_swap in 25.2.2 paragraph 7 from:</p>
<blockquote>
<p>Exchanges the values pointed to by the two iterators a and b.</p>
</blockquote>
<p>to</p>
<blockquote>
<p>
<tt>swap(*a, *b)</tt>.</p>
</blockquote>
<p><i>[post-Toronto: The LWG is concerned about possible
overspecification: there may be cases, such as Dave Abrahams's example
above, and such as vector&lt;bool&gt;'s iterators, where it makes more
sense for iter_swap to do something other than swap. If performance
is a concern, it may be better to have explicit complexity
requirements than to say how iter_swap should be implemented.]</i></p>
<p><i>[Redmond: Discussed, with no consensus. There was very little
support for the proposed resolution. Some people favored closing this
issue as NAD. Others favored a more complicated specification of
<tt>iter_swap</tt>, which might distinguish between ordinary iterators
and proxies. A possible new issue: how do we know that the iterators
passed to <tt>iter_swap</tt> have Assignable value types? (If this
new issue is real, it extends far beyond just
<tt>iter_swap</tt>.)]</i></p>
<hr>
<a name="197"><h3>197.&nbsp;max_size() underspecified</h3></a><p>
<b>Section:</b>&nbsp;20.1.5 <a href="lib-utilities.html#lib.allocator.requirements"> [lib.allocator.requirements]</a>, 23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Sawyer&nbsp; <b>Date:</b>&nbsp;21 Oct 1999</p>
<p>Must the value returned by max_size() be unchanged from call to call? </p>
<p>Must the value returned from max_size() be meaningful? </p>
<p>Possible meanings identified in lib-6827: </p>
<p>1) The largest container the implementation can support given &quot;best
case&quot; conditions - i.e. assume the run-time platform is &quot;configured to
the max&quot;, and no overhead from the program itself. This may possibly
be determined at the point the library is written, but certainly no
later than compile time.<br>
<br>
2) The largest container the program could create, given &quot;best case&quot;
conditions - i.e. same platform assumptions as (1), but take into
account any overhead for executing the program itself. (or, roughly
&quot;storage=storage-sizeof(program)&quot;). This does NOT include any resource
allocated by the program. This may (or may not) be determinable at
compile time.<br>
<br>
3) The largest container the current execution of the program could
create, given knowledge of the actual run-time platform, but again,
not taking into account any currently allocated resource. This is
probably best determined at program start-up.<br>
<br>
4) The largest container the current execution program could create at
the point max_size() is called (or more correctly at the point
max_size() returns :-), given it's current environment (i.e. taking
into account the actual currently available resources). This,
obviously, has to be determined dynamically each time max_size() is
called. </p>
<p><b>Proposed resolution:</b></p>
<p>Change 20.1.5 <a href="lib-utilities.html#lib.allocator.requirements"> [lib.allocator.requirements]</a> table 32 max_size() wording from:<br>
<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; the largest value that can meaningfully be
passed to X::allocate<br>
to:<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; the value of the largest constant expression
(5.19 <a href="expr.html#expr.const"> [expr.const]</a>) that could ever meaningfully be passed to X::allocate</p>
<p>
Change 23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a> table 65 max_size() wording from:<br>
<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; size() of the largest possible container.<br>
to:<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; the value of the largest constant expression
(5.19 <a href="expr.html#expr.const"> [expr.const]</a>) that could ever meaningfully be returned by X::size().
</p>
<p><i>[Kona: The LWG informally discussed this and asked Andy Sawyer to submit
an issue.]</i></p>
<p><i>[Tokyo: The LWG believes (1) above is the intended meaning.]</i></p>
<p><i>[Post-Tokyo: Beman Dawes supplied the above resolution at the
request of the LWG. 21.3.3 <a href="lib-strings.html#lib.string.capacity"> [lib.string.capacity]</a> was not changed because it
references max_size() in 23.1. The term &quot;compile-time&quot; was
avoided because it is not defined anywhere in the standard (even
though it is used several places in the library clauses).]</i></p>
<p><i>[Copenhagen: Exactly what <tt>max_size</tt> means is still
unclear. It may have a different meaning as a container member
function than as an allocator member function. For the latter,
it is probably best thought of as an architectural limit.
Nathan will provide new wording.]</i></p>
<hr>
<a name="198"><h3>198.&nbsp;Validity of pointers and references unspecified after iterator destruction</h3></a><p>
<b>Section:</b>&nbsp;24.1 <a href="lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Beman Dawes&nbsp; <b>Date:</b>&nbsp;3 Nov 1999</p>
<p>
Is a pointer or reference obtained from an iterator still valid after
destruction of the iterator?
</p>
<p>
Is a pointer or reference obtained from an iterator still valid after the value
of the iterator changes?
</p>
<blockquote>
<pre>
#include &lt;iostream&gt;
#include &lt;vector&gt;
#include &lt;iterator&gt;
int main()
{
typedef std::vector&lt;int&gt; vec_t;
vec_t v;
v.push_back( 1 );
// Is a pointer or reference obtained from an iterator still
// valid after destruction of the iterator?
int * p = &amp;*v.begin();
std::cout &lt;&lt; *p &lt;&lt; '\n'; // OK?
// Is a pointer or reference obtained from an iterator still
// valid after the value of the iterator changes?
vec_t::iterator iter( v.begin() );
p = &amp;*iter++;
std::cout &lt;&lt; *p &lt;&lt; '\n'; // OK?
return 0;
}
</pre>
</blockquote>
<p>The standard doesn't appear to directly address these
questions. The standard needs to be clarified. At least two real-world
cases have been reported where library implementors wasted
considerable effort because of the lack of clarity in the
standard. The question is important because requiring pointers and
references to remain valid has the effect for practical purposes of
prohibiting iterators from pointing to cached rather than actual
elements of containers.</p>
<p>The standard itself assumes that pointers and references obtained
from an iterator are still valid after iterator destruction or
change. The definition of reverse_iterator::operator*(), 24.4.1.3.3 <a href="lib-iterators.html#lib.reverse.iter.op.star"> [lib.reverse.iter.op.star]</a>, which returns a reference, defines
effects:</p>
<blockquote>
<pre>Iterator tmp = current;
return *--tmp;</pre>
</blockquote>
<p>The definition of reverse_iterator::operator-&gt;(), 24.4.1.3.4 <a href="lib-iterators.html#lib.reverse.iter.opref"> [lib.reverse.iter.opref]</a>, which returns a pointer, defines effects:</p>
<blockquote>
<pre>return &amp;(operator*());</pre>
</blockquote>
<p>Because the standard itself assumes pointers and references remain
valid after iterator destruction or change, the standard should say so
explicitly. This will also reduce the chance of user code breaking
unexpectedly when porting to a different standard library
implementation.</p>
<p><b>Proposed resolution:</b></p>
<p>Add a new paragraph to 24.1 <a href="lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>:</p>
<blockquote>
Destruction of an iterator may invalidate pointers and references
previously obtained from that iterator.
</blockquote>
<p>Replace paragraph 1 of 24.4.1.3.3 <a href="lib-iterators.html#lib.reverse.iter.op.star"> [lib.reverse.iter.op.star]</a> with:</p>
<blockquote>
<p><b>Effects:</b></p>
<pre>
this-&gt;tmp = current;
--this-&gt;tmp;
return *this-&gt;tmp;
</pre>
<p>
[<i>Note:</i> This operation must use an auxiliary member variable,
rather than a temporary variable, to avoid returning a reference that
persists beyond the lifetime of its associated iterator. (See
24.1 <a href="lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>.) The name of this member variable is shown for
exposition only. <i>--end note</i>]
</p>
</blockquote>
<p><i>[Post-Tokyo: The issue has been reformulated purely
in terms of iterators.]</i></p>
<p><i>[Pre-Toronto: Steve Cleary pointed out the no-invalidation
assumption by reverse_iterator. The issue and proposed resolution was
reformulated yet again to reflect this reality.]</i></p>
<p><i>[Copenhagen: Steve Cleary pointed out that reverse_iterator
assumes its underlying iterator has persistent pointers and
references. Andy Koenig pointed out that it is possible to rewrite
reverse_iterator so that it no longer makes such an assupmption.
However, this issue is related to issue <a href="lwg-active.html#299">299</a>. If we
decide it is intentional that <tt>p[n]</tt> may return by value
instead of reference when <tt>p</tt> is a Random Access Iterator,
other changes in reverse_iterator will be necessary.]</i></p>
<p><b>Rationale:</b></p>
<p>This issue has been discussed extensively. Note that it is
<i>not</i> an issue about the behavior of predefined iterators. It is
asking whether or not user-defined iterators are permitted to have
transient pointers and references. Several people presented examples
of useful user-defined iterators that have such a property; examples
include a B-tree iterator, and an &quot;iota iterator&quot; that doesn't point
to memory. Library implementors already seem to be able to cope with
such iterators: they take pains to avoid forming references to memory
that gets iterated past. The only place where this is a problem is
<tt>reverse_iterator</tt>, so this issue changes
<tt>reverse_iterator</tt> to make it work.</p>
<p>This resolution does not weaken any guarantees provided by
predefined iterators like <tt>list&lt;int&gt;::iterator</tt>.
Clause 23 should be reviewed to make sure that guarantees for
predefined iterators are as strong as users expect.</p>
<hr>
<a name="200"><h3>200.&nbsp;Forward iterator requirements don't allow constant iterators</h3></a><p>
<b>Section:</b>&nbsp;24.1.3 <a href="lib-iterators.html#lib.forward.iterators"> [lib.forward.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;19 Nov 1999</p>
<p>
In table 74, the return type of the expression <tt>*a</tt> is given
as <tt>T&amp;</tt>, where <tt>T</tt> is the iterator's value type.
For constant iterators, however, this is wrong. (&quot;Value type&quot;
is never defined very precisely, but it is clear that the value type
of, say, <tt>std::list&lt;int&gt;::const_iterator</tt> is supposed to be
<tt>int</tt>, not <tt>const int</tt>.)
</p>
<p><b>Proposed resolution:</b></p>
<p>
In table 74, in the <tt>*a</tt> and <tt>*r++</tt> rows, change the
return type from &quot;<tt>T&amp;</tt>&quot; to &quot;<tt>T&amp;</tt>
if <tt>X</tt> is mutable, otherwise <tt>const T&amp;</tt>&quot;.
In the <tt>a-&gt;m</tt> row, change the return type from
&quot;<tt>U&amp;</tt>&quot; to &quot;<tt>U&amp;</tt> if <tt>X</tt> is mutable,
otherwise <tt>const U&amp;</tt>&quot;.
</p>
<p><i>[Tokyo: The LWG believes this is the tip of a larger iceberg;
there are multiple const problems with the STL portion of the library
and that these should be addressed as a single package.&nbsp; Note
that issue <a href="lwg-closed.html#180">180</a> has already been declared NAD Future for
that very reason.]</i></p>
<p><i>[Redmond: the LWG thinks this is separable from other constness
issues. This issue is just cleanup; it clarifies language that was
written before we had iterator_traits. Proposed resolution was
modified: the original version only discussed *a. It was pointed out
that we also need to worry about *r++ and a-&gt;m.]</i></p>
<hr>
<a name="201"><h3>201.&nbsp;Numeric limits terminology wrong</h3></a><p>
<b>Section:</b>&nbsp;18.2.1 <a href="lib-support.html#lib.limits"> [lib.limits]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Stephen Cleary&nbsp; <b>Date:</b>&nbsp;21 Dec 1999</p>
<p>
In some places in this section, the terms &quot;fundamental types&quot; and
&quot;scalar types&quot; are used when the term &quot;arithmetic types&quot; is intended.
The current usage is incorrect because void is a fundamental type and
pointers are scalar types, neither of which should have
specializations of numeric_limits.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change 18.2 [lib.support.limits] para 1 from:</p>
<blockquote>
<p> The headers &lt;limits&gt;, &lt;climits&gt;, and &lt;cfloat&gt; supply characteristics of implementation-dependent fundamental types (3.9.1).</p>
</blockquote>
<p>to:</p>
<blockquote>
<p> The headers &lt;limits&gt;, &lt;climits&gt;, and &lt;cfloat&gt; supply characteristics of implementation-dependent arithmetic types (3.9.1).</p>
</blockquote>
<p>Change 18.2.1 [lib.limits] para 1 from:</p>
<blockquote>
<p> The numeric_limits component provides a C++ program with information about various properties of the implementation's representation of the fundamental
types.</p>
</blockquote>
<p>to:</p>
<blockquote>
<p> The numeric_limits component provides a C++ program with information about various properties of the implementation's representation of the arithmetic
types.</p>
</blockquote>
<p>Change 18.2.1 [lib.limits] para 2 from:</p>
<blockquote>
<p> Specializations shall be provided for each fundamental type. . .</p>
</blockquote>
<p>to:</p>
<blockquote>
<p> Specializations shall be provided for each arithmetic type. . .</p>
</blockquote>
<p>Change 18.2.1 [lib.limits] para 4 from:</p>
<blockquote>
<p> Non-fundamental standard types. . .</p>
</blockquote>
<p>to:</p>
<blockquote>
<p> Non-arithmetic standard types. . .</p>
</blockquote>
<p>Change 18.2.1.1 [lib.numeric.limits] para 1 from:</p>
<blockquote>
<p> The member is_specialized makes it possible to distinguish between fundamental types, which have specializations, and non-scalar types, which
do not.</p>
</blockquote>
<p>to:</p>
<blockquote>
<p> The member is_specialized makes it possible to distinguish between arithmetic types, which have specializations, and non-arithmetic types,
which do not.</p>
</blockquote>
<p><i>[post-Toronto: The opinion of the LWG is that the wording in the
standard, as well as the wording of the proposed resolution, is
flawed. The term &quot;arithmetic types&quot; is well defined in C
and C++, and it is not clear that the term is being used correctly.
It is also not clear that the term &quot;implementation
dependent&quot; has any useful meaning in this context. The biggest
problem is that numeric_limits seems to be intended both for built-in
types and for user-defined types, and the standard doesn't make it
clear how numeric_limits applies to each of those cases. A wholesale
review of numeric_limits is needed. A paper would be welcome.]</i></p>
<hr>
<a name="202"><h3>202.&nbsp;unique() effects unclear when predicate not an equivalence relation</h3></a><p>
<b>Section:</b>&nbsp;25.2.8 <a href="lib-algorithms.html#lib.alg.unique"> [lib.alg.unique]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Andrew Koenig&nbsp; <b>Date:</b>&nbsp;13 Jan 2000</p>
<p>
What should unique() do if you give it a predicate that is not an
equivalence relation? There are at least two plausible answers:
</p>
<blockquote>
<p>
1. You can't, because 25.2.8 says that it it &quot;eliminates all but
the first element from every consecutive group of equal
elements...&quot; and it wouldn't make sense to interpret &quot;equal&quot; as
meaning anything but an equivalence relation. [It also doesn't
make sense to interpret &quot;equal&quot; as meaning ==, because then there
would never be any sense in giving a predicate as an argument at
all.]
</p>
<p>
2. The word &quot;equal&quot; should be interpreted to mean whatever the
predicate says, even if it is not an equivalence relation
(and in particular, even if it is not transitive).
</p>
</blockquote>
<p>
The example that raised this question is from Usenet:
</p>
<blockquote>
<pre>int f[] = { 1, 3, 7, 1, 2 };
int* z = unique(f, f+5, greater&lt;int&gt;());</pre>
</blockquote>
<p>
If one blindly applies the definition using the predicate
greater&lt;int&gt;, and ignore the word &quot;equal&quot;, you get:
</p>
<blockquote>
<p>
Eliminates all but the first element from every consecutive group
of elements referred to by the iterator i in the range [first, last)
for which *i &gt; *(i - 1).
</p>
</blockquote>
<p>
The first surprise is the order of the comparison. If we wanted to
allow for the predicate not being an equivalence relation, then we
should surely compare elements the other way: pred(*(i - 1), *i). If
we do that, then the description would seem to say: &quot;Break the
sequence into subsequences whose elements are in strictly increasing
order, and keep only the first element of each subsequence&quot;. So the
result would be 1, 1, 2. If we take the description at its word, it
would seem to call for strictly DEcreasing order, in which case the
result should be 1, 3, 7, 2.<br>
<br>
In fact, the SGI implementation of unique() does neither: It yields 1,
3, 7.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change 25.2.8 <a href="lib-algorithms.html#lib.alg.unique"> [lib.alg.unique]</a> paragraph 1 to:</p>
<blockquote>
For a nonempty range, eliminates all but the first element from every
consecutive group of equivalent elements referred to by the iterator
<tt>i</tt> in the range (first, last) for which the following
conditions hold: <tt>*(i-1) == *i</tt> or <tt>pred(*(i-1), *i) !=
false</tt>.
</blockquote>
<p>
Also insert a new paragraph, paragraph 2a, that reads: &quot;Requires: The
comparison function must be an equivalence relation.&quot;
</p>
<p><i>[Redmond: discussed arguments for and against requiring the
comparison function to be an equivalence relation. Straw poll:
14-2-5. First number is to require that it be an equivalence
relation, second number is to explicitly not require that it be an
equivalence relation, third number is people who believe they need
more time to consider the issue. A separate issue: Andy Sawyer
pointed out that &quot;i-1&quot; is incorrect, since &quot;i&quot; can refer to the first
iterator in the range. Matt provided wording to address this
problem.]</i></p>
<p><b>Rationale:</b></p>
<p>The LWG also considered an alternative resolution: change
25.2.8 <a href="lib-algorithms.html#lib.alg.unique"> [lib.alg.unique]</a> paragraph 1 to:</p>
<blockquote>
For a nonempty range, eliminates all but the first element from every
consecutive group of elements referred to by the iterator
<tt>i</tt> in the range (first, last) for which the following
conditions hold: <tt>*(i-1) == *i</tt> or <tt>pred(*(i-1), *i) !=
false</tt>.
</blockquote>
<p>
Also insert a new paragraph, paragraph 1a, that reads: &quot;Notes: The
comparison function need not be an equivalence relation.&quot;
</p>
<p>Informally: the proposed resolution imposes an explicit requirement
that the comparison function be an equivalence relation. The
alternative resolution does not, and it gives enough information so
that the behavior of unique() for a non-equivalence relation is
specified. Both resolutions are consistent with the behavior of
existing implementations.</p>
<hr>
<a name="225"><h3>225.&nbsp;std:: algorithms use of other unqualified algorithms</h3></a><p>
<b>Section:</b>&nbsp;17.4.4.3 <a href="lib-intro.html#lib.global.functions"> [lib.global.functions]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Dave Abrahams&nbsp; <b>Date:</b>&nbsp;01 Apr 2000</p>
<p>Are algorithms in std:: allowed to use other algorithms without qualification, so functions in
user namespaces might be found through Koenig lookup?</p>
<p>For example, a popular standard library implementation includes this
implementation of std::unique:</p>
<blockquote>
<pre>namespace std {
template &lt;class _ForwardIter&gt;
_ForwardIter unique(_ForwardIter __first, _ForwardIter __last) {
__first = adjacent_find(__first, __last);
return unique_copy(__first, __last, __first);
}
}</pre>
</blockquote>
<p>Imagine two users on opposite sides of town, each using unique on his own
sequences bounded by my_iterators . User1 looks at his standard library
implementation and says, &quot;I know how to implement a more efficient
unique_copy for my_iterators&quot;, and writes:</p>
<blockquote>
<pre>namespace user1 {
class my_iterator;
// faster version for my_iterator
my_iterator unique_copy(my_iterator, my_iterator, my_iterator);
}</pre>
</blockquote>
<p>user1::unique_copy() is selected by Koenig lookup, as he intended.</p>
<p>User2 has other needs, and writes:</p>
<blockquote>
<pre>namespace user2 {
class my_iterator;
// Returns true iff *c is a unique copy of *a and *b.
bool unique_copy(my_iterator a, my_iterator b, my_iterator c);
}</pre>
</blockquote>
<p>User2 is shocked to find later that his fully-qualified use of
std::unique(user2::my_iterator, user2::my_iterator, user2::my_iterator) fails to
compile (if he's lucky). Looking in the standard, he sees the following Effects
clause for unique():</p>
<blockquote>
<p>Effects: Eliminates all but the first element from every consecutive group
of equal elements referred to by the iterator i in the range [first, last) for
which the following corresponding conditions hold: *i == *(i - 1) or pred(*i,
*(i - 1)) != false</p>
</blockquote>
<p>The standard gives user2 absolutely no reason to think he can interfere with
std::unique by defining names in namespace user2. His standard library has been
built with the template export feature, so he is unable to inspect the
implementation. User1 eventually compiles his code with another compiler, and
his version of unique_copy silently stops being called. Eventually, he realizes
that he was depending on an implementation detail of his library and had no
right to expect his unique_copy() to be called portably.</p>
<p>On the face of it, and given above scenario, it may seem obvious that the
implementation of unique() shown is non-conforming because it uses unique_copy()
rather than ::std::unique_copy(). Most standard library implementations,
however, seem to disagree with this notion.</p>
<p> <i>[Tokyo:&nbsp; Steve Adamczyk from
the core working group indicates that &quot;std::&quot; is sufficient;&nbsp;
leading &quot;::&quot; qualification is not required because any namespace
qualification is sufficient to suppress Koenig lookup.]</i>
</p>
<p><b>Proposed resolution:</b></p>
<p>Add a paragraph and a note at the end of
17.4.4.3 <a href="lib-intro.html#lib.global.functions"> [lib.global.functions]</a>:</p>
<blockquote>
<p>Unless otherwise specified, no global or non-member function in the
standard library shall use a function from another namespace which is
found through <i>argument-dependent name lookup</i> (3.4.2 <a href="basic.html#basic.lookup.koenig"> [basic.lookup.koenig]</a>).</p>
<p>[Note: the phrase &quot;unless otherwise specified&quot; is intended to
allow Koenig lookup in cases like that of ostream_iterators:<br>
<br>
Effects:</p>
<blockquote>
<p>*out_stream &lt;&lt; value;<br>
if(delim != 0) *out_stream &lt;&lt; delim;<br>
return (*this);</p>
<p>--end note]</p>
</blockquote>
</blockquote>
<p><i>[Tokyo: The LWG agrees that this is a defect in the standard, but
is as yet unsure if the proposed resolution is the best
solution. Furthermore, the LWG believes that the same problem of
unqualified library names applies to wording in the standard itself,
and has opened issue <a href="lwg-active.html#229">229</a> accordingly. Any resolution of
issue <a href="lwg-active.html#225">225</a> should be coordinated with the resolution of
issue <a href="lwg-active.html#229">229</a>.]</i></p>
<p><i>[Toronto: The LWG is not sure if this is a defect in the
standard. Most LWG members believe that an implementation of
<tt>std::unique</tt> like the one quoted in this issue is already
illegal, since, under certain circumstances, its semantics are not
those specified in the standard. The standard's description of
<tt>unique</tt> does not say that overloading <tt>adjacent_find</tt>
should have any effect.]</i></p>
<hr>
<a name="226"><h3>226.&nbsp;User supplied specializations or overloads of namespace std function templates</h3></a><p>
<b>Section:</b>&nbsp;17.4.3.1 <a href="lib-intro.html#lib.reserved.names"> [lib.reserved.names]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Dave Abrahams&nbsp; <b>Date:</b>&nbsp;01 Apr 2000</p>
<p>The issues are:&nbsp;</p>
<p>1. How can a 3rd party library implementor (lib1) write a version of a standard
algorithm which is specialized to work with his own class template?&nbsp;</p>
<p>2. How can another library implementor (lib2) write a generic algorithm which
will take advantage of the specialized algorithm in lib1?</p>
<p>This appears to be the only viable answer under current language rules:</p>
<blockquote>
<pre>namespace lib1
{
// arbitrary-precision numbers using T as a basic unit
template &lt;class T&gt;
class big_num { //...
};
</pre>
<pre> // defining this in namespace std is illegal (it would be an
// overload), so we hope users will rely on Koenig lookup
template &lt;class T&gt;
void swap(big_int&lt;T&gt;&amp;, big_int&lt;T&gt;&amp;);
}</pre>
<pre>#include &lt;algorithm&gt;
namespace lib2
{
template &lt;class T&gt;
void generic_sort(T* start, T* end)
{
...
// using-declaration required so we can work on built-in types
using std::swap;
// use Koenig lookup to find specialized algorithm if available
swap(*x, *y);
}
}</pre>
</blockquote>
<p>This answer has some drawbacks. First of all, it makes writing lib2 difficult
and somewhat slippery. The implementor needs to remember to write the
using-declaration, or generic_sort will fail to compile when T is a built-in
type. The second drawback is that the use of this style in lib2 effectively
&quot;reserves&quot; names in any namespace which defines types which may
eventually be used with lib2. This may seem innocuous at first when applied to
names like swap, but consider more ambiguous names like unique_copy() instead.
It is easy to imagine the user wanting to define these names differently in his
own namespace. A definition with semantics incompatible with the standard
library could cause serious problems (see issue <a href="lwg-active.html#225">225</a>).</p>
<p>Why, you may ask, can't we just partially specialize std::swap()? It's
because the language doesn't allow for partial specialization of function
templates. If you write:</p>
<blockquote>
<pre>namespace std
{
template &lt;class T&gt;
void swap(lib1::big_int&lt;T&gt;&amp;, lib1::big_int&lt;T&gt;&amp;);
}</pre>
</blockquote>
<p>You have just overloaded std::swap, which is illegal under the current
language rules. On the other hand, the following full specialization is legal:</p>
<blockquote>
<pre>namespace std
{
template &lt;&gt;
void swap(lib1::other_type&amp;, lib1::other_type&amp;);
}</pre>
</blockquote>
<p>This issue reflects concerns raised by the &quot;Namespace issue
with specialized swap&quot; thread on comp.lang.c++.moderated. A
similar set of concerns was earlier raised on the boost.org mailing
list and the ACCU-general mailing list. Also see library reflector
message c++std-lib-7354.</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Tokyo: Summary, &quot;There is no conforming way to extend
std::swap for user defined templates.&quot;&nbsp; The LWG agrees that
there is a problem.&nbsp; Would like more information before
proceeding. This may be a core issue. Core issue 229 has been opened
to discuss the core aspects of this problem. It was also noted that
submissions regarding this issue have been received from several
sources, but too late to be integrated into the issues list.
]</i></p>
<p><i>[Post-Tokyo: A paper with several proposed resolutions,
J16/00-0029==WG21/N1252, &quot;Shades of namespace std functions
&quot; by Alan Griffiths, is in the Post-Tokyo mailing. It
should be considered a part of this issue.]</i></p>
<p><i>[Toronto: Dave Abrahams and Peter Dimov have proposed a
resolution that involves core changes: it would add partial
specialization of function template. The Core Working Group is
reluctant to add partial specialization of function templates. It is
viewed as a large change, CWG believes that proposal presented leaves
some syntactic issues unanswered; if the CWG does add partial
specialization of function templates, it wishes to develop its own
proposal. The LWG continues to believe that there is a serious
problem: there is no good way for users to force the library to use
user specializations of generic standard library functions, and in
certain cases (e.g. transcendental functions called by
<tt>valarray</tt> and <tt>complex</tt>) this is important. Koenig
lookup isn't adequate, since names within the library must be
qualified with <tt>std</tt> (see issue 225), specialization doesn't
work (we don't have partial specialization of function templates), and
users aren't permitted to add overloads within namespace std.
]</i></p>
<p><i>[Copenhagen: Discussed at length, with no consensus. Relevant
papers in the pre-Copenhagen mailing: N1289, N1295, N1296. Discussion
focused on four options. (1) Relax restrictions on overloads within
namespace std. (2) Mandate that the standard library use unqualified
calls for <tt>swap</tt> and possibly other functions. (3) Introduce
helper class templates for <tt>swap</tt> and possibly other functions.
(4) Introduce partial specialization of function templates. Every
option had both support and opposition. Straw poll (first number is
support, second is strongly opposed): (1) 6, 4; (2) 6, 7; (3) 3, 8;
(4) 4, 4.]</i></p>
<p><i>[Redmond: Discussed, again no consensus. Herb presented an
argument that a user who is defining a type <tt>T</tt> with an
associated <tt>swap</tt> should not be expected to put that
<tt>swap</tt> in namespace std, either by overloading or by partial
specialization. The argument is that <tt>swap</tt> is part of
<tt>T</tt>'s interface, and thus should to in the same namespace as
<tt>T</tt> and only in that namespace. If we accept this argument,
the consequence is that standard library functions should use
unqualified call of <tt>swap</tt>. (And which other functions? Any?)
A small group (Nathan, Howard, Jeremy, Dave, Matt, Walter, Marc) will
try to put together a proposal before the next meeting.]</i></p>
<hr>
<a name="229"><h3>229.&nbsp;Unqualified references of other library entities</h3></a><p>
<b>Section:</b>&nbsp;17.4.1.1 <a href="lib-intro.html#lib.contents"> [lib.contents]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Steve Clamage&nbsp; <b>Date:</b>&nbsp;19 Apr 2000</p>
<p>Throughout the library chapters, the descriptions of library entities refer
to other library entities without necessarily qualifying the names.</p>
<p>For example, section 25.2.2 &quot;Swap&quot; describes the effect of
swap_ranges in terms of the unqualified name &quot;swap&quot;. This section
could reasonably be interpreted to mean that the library must be implemented so
as to do a lookup of the unqualified name &quot;swap&quot;, allowing users to
override any ::std::swap function when Koenig lookup applies.</p>
<p>Although it would have been best to use explicit qualification with
&quot;::std::&quot; throughout, too many lines in the standard would have to be
adjusted to make that change in a Technical Corrigendum.</p>
<p>Issue <a href="lwg-defects.html#182">182</a>, which addresses qualification of
<tt>size_t</tt>, is a special case of this.
</p>
<p><b>Proposed resolution:</b></p>
<p>To section 17.4.1.1 &quot;Library contents&quot; Add the following paragraph:</p>
<blockquote>
<p>Whenever a name x defined in the standard library is mentioned, the name x
is assumed to be fully qualified as ::std::x, unless explicitly described
otherwise. For example, if the Effects section for library function F is
described as calling library function G, the function ::std::G is meant.</p>
</blockquote>
<p><i>[Post-Tokyo: Steve Clamage submitted this issue at the request of
the LWG to solve a problem in the standard itself similar to the
problem within implementations of library identified by issue <a href="lwg-active.html#225">225</a>. Any resolution of issue <a href="lwg-active.html#225">225</a> should be
coordinated with the resolution of this issue.]</i></p>
<p><i>[post-Toronto: Howard is undecided about whether it is
appropriate for all standard library function names referred to in
other standard library functions to be explicitly qualified by
<tt>std</tt>: it is common advice that users should define global
functions that operate on their class in the same namespace as the
class, and this requires argument-dependent lookup if those functions
are intended to be called by library code. Several LWG members are
concerned that valarray appears to require argument-dependent lookup,
but that the wording may not be clear enough to fall under
&quot;unless explicitly described otherwise&quot;.]</i></p>
<hr>
<a name="231"><h3>231.&nbsp;Precision in iostream?</h3></a><p>
<b>Section:</b>&nbsp;22.2.2.2.2 <a href="lib-locales.html#lib.facet.num.put.virtuals"> [lib.facet.num.put.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;James Kanze, Stephen Clamage&nbsp; <b>Date:</b>&nbsp; 25 Apr 2000</p>
<p>What is the following program supposed to output?</p>
<pre>#include &lt;iostream&gt;
int
main()
{
std::cout.setf( std::ios::scientific , std::ios::floatfield ) ;
std::cout.precision( 0 ) ;
std::cout &lt;&lt; 1.00 &lt;&lt; '\n' ;
return 0 ;
}</pre>
<p>From my C experience, I would expect &quot;1e+00&quot;; this is what
<tt>printf(&quot;%.0e&quot; , 1.00 );</tt> does. G++ outputs
&quot;1.000000e+00&quot;.</p>
<p>The only indication I can find in the standard is 22.2.2.2.2/11,
where it says &quot;For conversion from a floating-point type, if
(flags &amp; fixed) != 0 or if str.precision() &gt; 0, then
str.precision() is specified in the conversion specification.&quot;
This is an obvious error, however, fixed is not a mask for a field,
but a value that a multi-bit field may take -- the results of and'ing
fmtflags with ios::fixed are not defined, at least not if
ios::scientific has been set. G++'s behavior corresponds to what might
happen if you do use (flags &amp; fixed) != 0 with a typical
implementation (floatfield == 3 &lt;&lt; something, fixed == 1
&lt;&lt; something, and scientific == 2 &lt;&lt; something).</p>
<p>Presumably, the intent is either (flags &amp; floatfield) != 0, or
(flags &amp; floatfield) == fixed; the first gives something more or
less like the effect of precision in a printf floating point
conversion. Only more or less, of course. In order to implement printf
formatting correctly, you must know whether the precision was
explicitly set or not. Say by initializing it to -1, instead of 6, and
stating that for floating point conversions, if precision &lt; -1, 6
will be used, for fixed point, if precision &lt; -1, 1 will be used,
etc. Plus, of course, if precision == 0 and flags &amp; floatfield ==
0, 1 should be = used. But it probably isn't necessary to emulate all
of the anomalies of printf:-).</p>
<p><b>Proposed resolution:</b></p>
<p>
In 22.2.2.2.2 <a href="lib-locales.html#lib.facet.num.put.virtuals"> [lib.facet.num.put.virtuals]</a>, paragraph 11, change
&quot;if <tt>(flags &amp; fixed) != 0</tt>&quot; to
&quot;if <tt>(flags &amp; floatfield) == fixed ||
(flags &amp; floatfield) == scientific</tt>&quot;
</p>
<p><b>Rationale:</b></p>
<p>The floatfield determines whether numbers are formatted as if
with %f, %e, or %g. If the <tt>fixed</tt> bit is set, it's %f,
if <tt>scientific</tt> it's %e, and if both bits are set, or
neither, it's %e.</p>
<p>Turning to the C standard, a precision of 0 is meaningful
for %f and %e, but not for %g: for %g, precision 0 is taken
to be the same as precision 1.</p>
<p>The proposed resolution has the effect that the output of
the above program will be &quot;1e+00&quot;.</p>
<hr>
<a name="233"><h3>233.&nbsp;Insertion hints in associative containers</h3></a><p>
<b>Section:</b>&nbsp;23.1.2 <a href="lib-containers.html#lib.associative.reqmts"> [lib.associative.reqmts]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Andrew Koenig&nbsp; <b>Date:</b>&nbsp;30 Apr 2000</p>
<p>
If <tt>mm</tt> is a multimap and <tt>p</tt> is an iterator
into the multimap, then <tt>mm.insert(p, x)</tt> inserts
<tt>x</tt> into <tt>mm</tt> with <tt>p</tt> as a hint as
to where it should go. Table 69 claims that the execution time is
amortized constant if the insert winds up taking place adjacent to
<tt>p</tt>, but does not say when, if ever, this is guaranteed to
happen. All it says it that <tt>p</tt> is a hint as to where to
insert.
</p>
<p>
The question is whether there is any guarantee about the relationship
between <tt>p</tt> and the insertion point, and, if so, what it
is.
</p>
<p>
I believe the present state is that there is no guarantee: The user
can supply <tt>p</tt>, and the implementation is allowed to
disregard it entirely.
</p>
<p>
<b>Additional comments from Nathan:</b><br>
The vote [in Redmond] was on whether to elaborately specify the use of
the hint, or to require behavior only if the value could be inserted
adjacent to the hint. I would like to ensure that we have a chance to
vote for a deterministic treatment: &quot;before, if possible, otherwise
after, otherwise anywhere appropriate&quot;, as an alternative to the
proposed &quot;before or after, if possible, otherwise [...]&quot;.
</p>
<p><b>Proposed resolution:</b></p>
<p>In table 69 &quot;Associative Container Requirements&quot; in 23.1.2 <a href="lib-containers.html#lib.associative.reqmts"> [lib.associative.reqmts]</a>, in the row for <tt>a.insert(p, t)</tt>,
change</p>
<blockquote>
iterator p is a hint pointing to where the insert
should start to search.
</blockquote>
<p>to</p>
<blockquote>
insertion adjacent to iterator p is preferred if
more than one insertion point is valid.
</blockquote>
<p>and change</p>
<blockquote>
logarithmic in general, but amortized constant if
t is inserted right after p.
</blockquote>
<p>to</p>
<blockquote>
logarithmic in general, but amortized constant if
t is inserted adjacent to iterator p.
</blockquote>
<p><i>[Toronto: there was general agreement that this is a real defect:
when inserting an element x into a multiset that already contains
several copies of x, there is no way to know whether the hint will be
used. There was some support for an alternative resolution: we check
on both sides of the hint (both before and after, in that order). If
either is the correct location, the hint is used; otherwise it is not.
This would be different from the original proposed resolution, because
in the proposed resolution the hint will be used even if it is very
far from the insertion point. JC van Winkel supplied precise wording
for both options.]</i></p>
<p><i>[Copenhagen: the LWG looked at both options, and preferred the
original. This preference is contingent on seeing a reference
implementation showing that it is possible to implement this
requirement without loss of efficiency.]</i></p>
<p><i>[Redmond: The LWG was reluctant to adopt the proposal that
emerged from Copenhagen: it seemed excessively complicated, and went
beyond fixing the defect that we identified in Toronto. PJP provided
the new wording described in this issue. Nathan agrees that we
shouldn't adopt the more detailed semantics, and notes: &quot;we know that
you can do it efficiently enough with a red-black tree, but there are
other (perhaps better) balanced tree techniques that might differ
enough to make the detailed semantics hard to satisfy.&quot;]</i></p>
<hr>
<a name="239"><h3>239.&nbsp;Complexity of unique() and/or unique_copy incorrect</h3></a><p>
<b>Section:</b>&nbsp;25.2.8 <a href="lib-algorithms.html#lib.alg.unique"> [lib.alg.unique]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Angelika Langer&nbsp; <b>Date:</b>&nbsp;May 15 2000</p>
<p>The complexity of unique and unique_copy are inconsistent with each
other and inconsistent with the implementations.&nbsp; The standard
specifies:</p>
<p>for unique():</p>
<blockquote>-3- Complexity: If the range (last - first) is not empty, exactly
(last - first) - 1 applications of the corresponding predicate, otherwise
no applications of the predicate.</blockquote>
<p>for unique_copy():</p>
<blockquote>-7- Complexity: Exactly last - first applications of the corresponding
predicate.</blockquote>
<p>
The implementations do it the other way round: unique() applies the
predicate last-first times and unique_copy() applies it last-first-1
times.</p>
<p>As both algorithms use the predicate for pair-wise comparison of
sequence elements I don't see a justification for unique_copy()
applying the predicate last-first times, especially since it is not
specified to which pair in the sequence the predicate is applied
twice.</p>
<p><b>Proposed resolution:</b></p>
<p>Change both complexity sections in 25.2.8 <a href="lib-algorithms.html#lib.alg.unique"> [lib.alg.unique]</a> to:</p>
<blockquote>Complexity: For nonempty ranges, exactly last - first - 1
applications of the corresponding predicate.</blockquote>
<hr>
<a name="240"><h3>240.&nbsp;Complexity of adjacent_find() is meaningless</h3></a><p>
<b>Section:</b>&nbsp;25.1.5 <a href="lib-algorithms.html#lib.alg.adjacent.find"> [lib.alg.adjacent.find]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Angelika Langer&nbsp; <b>Date:</b>&nbsp;May 15 2000</p>
<p>The complexity section of adjacent_find is defective:</p>
<blockquote>
<pre>
template &lt;class ForwardIterator&gt;
ForwardIterator adjacent_find(ForwardIterator first, ForwardIterator last
BinaryPredicate pred);
</pre>
<p>-1- Returns: The first iterator i such that both i and i + 1 are in
the range [first, last) for which the following corresponding
conditions hold: *i == *(i + 1), pred(*i, *(i + 1)) != false. Returns
last if no such iterator is found.</p>
<p>-2- Complexity: Exactly find(first, last, value) - first applications
of the corresponding predicate.
</p>
</blockquote>
<p>In the Complexity section, it is not defined what &quot;value&quot;
is supposed to mean. My best guess is that &quot;value&quot; means an
object for which one of the conditions pred(*i,value) or
pred(value,*i) is true, where i is the iterator defined in the Returns
section. However, the value type of the input sequence need not be
equality-comparable and for this reason the term find(first, last,
value) - first is meaningless.</p>
<p>A term such as find_if(first, last, bind2nd(pred,*i)) - first or
find_if(first, last, bind1st(pred,*i)) - first might come closer to
the intended specification. Binders can only be applied to function
objects that have the function call operator declared const, which is
not required of predicates because they can have non-const data
members. For this reason, a specification using a binder could only be
an &quot;as-if&quot; specification.</p>
<p><b>Proposed resolution:</b></p>
<p>Change the complexity section in 25.1.5 <a href="lib-algorithms.html#lib.alg.adjacent.find"> [lib.alg.adjacent.find]</a> to:</p>
<blockquote>
For a nonempty range, exactly <tt>min((<i>i</i> - <i>first</i>) + 1,
(<i>last</i> - <i>first</i>) - 1)</tt> applications of the
corresponding predicate, where <i>i</i> is <tt>adjacent_find</tt>'s
return value.
</blockquote>
<p><i>[Copenhagen: the original resolution specified an upper
bound. The LWG preferred an exact count.]</i></p>
<hr>
<a name="241"><h3>241.&nbsp;Does unique_copy() require CopyConstructible and Assignable?</h3></a><p>
<b>Section:</b>&nbsp;25.2.8 <a href="lib-algorithms.html#lib.alg.unique"> [lib.alg.unique]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Angelika Langer&nbsp; <b>Date:</b>&nbsp;May 15 2000</p>
<p>Some popular implementations of unique_copy() create temporary
copies of values in the input sequence, at least if the input iterator
is a pointer. Such an implementation is built on the assumption that
the value type is CopyConstructible and Assignable.</p>
<p>It is common practice in the standard that algorithms explicitly
specify any additional requirements that they impose on any of the
types used by the algorithm. An example of an algorithm that creates
temporary copies and correctly specifies the additional requirements
is accumulate(), 26.4.1 <a href="lib-numerics.html#lib.accumulate"> [lib.accumulate]</a>.</p>
<p>Since the specifications of unique() and unique_copy() do not
require CopyConstructible and Assignable of the InputIterator's value
type the above mentioned implementations are not standard-compliant. I
cannot judge whether this is a defect in the standard or a defect in
the implementations.</p>
<p><b>Proposed resolution:</b></p>
<p>In 25.2.8 change:</p>
<blockquote>
-4- Requires: The ranges [first, last) and [result, result+(last-first))
shall not overlap.
</blockquote>
<p>to:</p>
<blockquote>
-4- Requires: The ranges [first, last) and [result, result+(last-first))
shall not overlap. The expression *result = *first must be valid. If
both InputIterator and OutputIterator do not meet the requirements of
forward iterator then the value type of InputIterator must be copy
constructible. Otherwise copy constructible is not required.
</blockquote>
<p><i>[Redmond: the original proposed resolution didn't impose an
explicit requirement that the iterator's value type must be copy
constructible, on the grounds that an input iterator's value type must
always be copy constructible. Not everyone in the LWG thought that
this requirement was clear from table 72. It has been suggested that
it might be possible to implement <tt>unique_copy</tt> without
requiring assignability, although current implementations do impose
that requirement. Howard provided new wording.]</i></p>
<hr>
<a name="247"><h3>247.&nbsp;<tt>vector</tt>, <tt>deque::insert</tt> complexity</h3></a><p>
<b>Section:</b>&nbsp;23.2.4.3 <a href="lib-containers.html#lib.vector.modifiers"> [lib.vector.modifiers]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Lisa Lippincott&nbsp; <b>Date:</b>&nbsp;06 June 2000</p>
<p>Paragraph 2 of 23.2.4.3 [lib.vector.modifiers] describes the complexity
of <tt>vector::insert</tt>:</p>
<blockquote>
Complexity: If first and last are forward iterators, bidirectional
iterators, or random access iterators, the complexity is linear in
the number of elements in the range [first, last) plus the distance
to the end of the vector. If they are input iterators, the complexity
is proportional to the number of elements in the range [first, last)
times the distance to the end of the vector.
</blockquote>
<p>First, this fails to address the non-iterator forms of
<tt>insert</tt>.</p>
<p>Second, the complexity for input iterators misses an edge case --
it requires that an arbitrary number of elements can be added at
the end of a <tt>vector</tt> in constant time.</p>
<p>At the risk of strengthening the requirement, I suggest simply</p>
<blockquote>
Complexity: The complexity is linear in the number of elements
inserted plus the distance to the end of the vector.
</blockquote>
<p>For input iterators, one may achieve this complexity by first
inserting at the end of the <tt>vector</tt>, and then using
<tt>rotate</tt>.</p>
<p>I looked to see if <tt>deque</tt> had a similar problem, and was
surprised to find that <tt>deque</tt> places no requirement on the
complexity of inserting multiple elements (23.2.1.3 <a href="lib-containers.html#lib.deque.modifiers"> [lib.deque.modifiers]</a>,
paragraph 3):</p>
<blockquote>
Complexity: In the worst case, inserting a single element into a
deque takes time linear in the minimum of the distance from the
insertion point to the beginning of the deque and the distance
from the insertion point to the end of the deque. Inserting a
single element either at the beginning or end of a deque always
takes constant time and causes a single call to the copy constructor
of T.
</blockquote>
<p>I suggest:</p>
<blockquote>
Complexity: The complexity is linear in the number of elements
inserted plus the shorter of the distances to the beginning and
end of the deque. Inserting a single element at either the
beginning or the end of a deque causes a single call to the copy
constructor of T.
</blockquote>
<p><b>Proposed resolution:</b></p>
<p><i>[Toronto: It's agreed that there is a defect in complexity of
multi-element insert for vector and deque. For vector, the complexity
should probably be something along the lines of <tt>c<sub>1</sub> * N
+ c<sub>2</sub> * distance(i, end())</tt>. However, there is some
concern about whether it is reasonable to amortize away the copies
that we get from a reallocation whenever we exceed the vector's
capacity. For deque, the situation is somewhat less clear. Deque is
notoriously complicated, and we may not want to impose complexity
requirements that would imply any implementation technique more
complicated than a while loop whose body is a single-element
insert.]</i></p>
<hr>
<a name="253"><h3>253.&nbsp;valarray helper functions are almost entirely useless</h3></a><p>
<b>Section:</b>&nbsp;26.3.2.1 <a href="lib-numerics.html#lib.valarray.cons"> [lib.valarray.cons]</a>, 26.3.2.2 <a href="lib-numerics.html#lib.valarray.assign"> [lib.valarray.assign]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Robert Klarer&nbsp; <b>Date:</b>&nbsp;31 Jul 2000</p>
<p>This discussion is adapted from message c++std-lib-7056 posted
November 11, 1999. I don't think that anyone can reasonably claim
that the problem described below is NAD.</p>
<p>These valarray constructors can never be called:</p>
<pre>
template &lt;class T&gt;
valarray&lt;T&gt;::valarray(const slice_array&lt;T&gt; &amp;);
template &lt;class T&gt;
valarray&lt;T&gt;::valarray(const gslice_array&lt;T&gt; &amp;);
template &lt;class T&gt;
valarray&lt;T&gt;::valarray(const mask_array&lt;T&gt; &amp;);
template &lt;class T&gt;
valarray&lt;T&gt;::valarray(const indirect_array&lt;T&gt; &amp;);
</pre>
<p>Similarly, these valarray assignment operators cannot be
called:</p>
<pre>
template &lt;class T&gt;
valarray&lt;T&gt; valarray&lt;T&gt;::operator=(const slice_array&lt;T&gt; &amp;);
template &lt;class T&gt;
valarray&lt;T&gt; valarray&lt;T&gt;::operator=(const gslice_array&lt;T&gt; &amp;);
template &lt;class T&gt;
valarray&lt;T&gt; valarray&lt;T&gt;::operator=(const mask_array&lt;T&gt; &amp;);
template &lt;class T&gt;
valarray&lt;T&gt; valarray&lt;T&gt;::operator=(const indirect_array&lt;T&gt; &amp;);
</pre>
<p>Please consider the following example:</p>
<pre>
#include &lt;valarray&gt;
using namespace std;
int main()
{
valarray&lt;double&gt; va1(12);
valarray&lt;double&gt; va2(va1[slice(1,4,3)]); // line 1
}
</pre>
<p>Since the valarray va1 is non-const, the result of the sub-expression
va1[slice(1,4,3)] at line 1 is an rvalue of type const
std::slice_array&lt;double&gt;. This slice_array rvalue is then used to
construct va2. The constructor that is used to construct va2 is
declared like this:</p>
<pre>
template &lt;class T&gt;
valarray&lt;T&gt;::valarray(const slice_array&lt;T&gt; &amp;);
</pre>
<p>Notice the constructor's const reference parameter. When the
constructor is called, a slice_array must be bound to this reference.
The rules for binding an rvalue to a const reference are in 8.5.3,
paragraph 5 (see also 13.3.3.1.4). Specifically, paragraph 5
indicates that a second slice_array rvalue is constructed (in this
case copy-constructed) from the first one; it is this second rvalue
that is bound to the reference parameter. Paragraph 5 also requires
that the constructor that is used for this purpose be callable,
regardless of whether the second rvalue is elided. The
copy-constructor in this case is not callable, however, because it is
private. Therefore, the compiler should report an error.</p>
<p>Since slice_arrays are always rvalues, the valarray constructor that has a
parameter of type const slice_array&lt;T&gt; &amp; can never be called. The
same reasoning applies to the three other constructors and the four
assignment operators that are listed at the beginning of this post.
Furthermore, since these functions cannot be called, the valarray helper
classes are almost entirely useless.</p>
<p><b>Proposed resolution:</b></p>
<p>slice_array:</p>
<ul>
<li> remove the copy constructor and copy-assignment operator declarations
from the slice_array class template definition in 26.3.5 <a href="lib-numerics.html#lib.template.slice.array"> [lib.template.slice.array]</a> </li>
<li> remove paragraph 3 of 26.3.5 <a href="lib-numerics.html#lib.template.slice.array"> [lib.template.slice.array]</a>
</li>
<li> remove the copy constructor declaration from 26.3.5.1 <a href="lib-numerics.html#lib.cons.slice.arr"> [lib.cons.slice.arr]</a>
</li>
<li> change paragraph 1 of 26.3.5.1 <a href="lib-numerics.html#lib.cons.slice.arr"> [lib.cons.slice.arr]</a> to read &quot;This constructor is declared
to be private. This constructor need not be defined.&quot;</li>
<li> remove the copy-assignment operator declaration from 26.3.5.2 <a href="lib-numerics.html#lib.slice.arr.assign"> [lib.slice.arr.assign]</a>
</li>
<li> remove the first sentence of paragraph 1 of 26.3.5.2 <a href="lib-numerics.html#lib.slice.arr.assign"> [lib.slice.arr.assign]</a>
</li>
<li> Change the first two words of the second sentence of paragraph 1 of
26.3.5.2 <a href="lib-numerics.html#lib.slice.arr.assign"> [lib.slice.arr.assign]</a> to &quot;This function.&quot;</li>
</ul>
<p>gslice_array:</p>
<ul>
<li> remove the copy constructor and copy-assignment operator declarations
from the gslice_array class template definition in 26.3.7 <a href="lib-numerics.html#lib.template.gslice.array"> [lib.template.gslice.array]</a> </li>
<li> remove the note in paragraph 3 of 26.3.7 <a href="lib-numerics.html#lib.template.gslice.array"> [lib.template.gslice.array]</a>
</li>
<li> remove the copy constructor declaration from 26.3.7.1 <a href="lib-numerics.html#lib.gslice.array.cons"> [lib.gslice.array.cons]</a>
</li>
<li> change paragraph 1 of 26.3.7.1 <a href="lib-numerics.html#lib.gslice.array.cons"> [lib.gslice.array.cons]</a> to read &quot;This constructor is declared
to be private. This constructor need not be defined.&quot;</li>
<li> remove the copy-assignment operator declaration from 26.3.7.2 <a href="lib-numerics.html#lib.gslice.array.assign"> [lib.gslice.array.assign]</a>
</li>
<li> remove the first sentence of paragraph 1 of 26.3.7.2 <a href="lib-numerics.html#lib.gslice.array.assign"> [lib.gslice.array.assign]</a>
</li>
<li> Change the first two words of the second sentence of paragraph 1 of
26.3.7.2 <a href="lib-numerics.html#lib.gslice.array.assign"> [lib.gslice.array.assign]</a> to &quot;This function.&quot;</li>
</ul>
<p>mask_array:</p>
<ul>
<li> remove the copy constructor and copy-assignment operator declarations
from the mask_array class template definition in 26.3.8 <a href="lib-numerics.html#lib.template.mask.array"> [lib.template.mask.array]</a> </li>
<li> remove the note in paragraph 2 of 26.3.8 <a href="lib-numerics.html#lib.template.mask.array"> [lib.template.mask.array]</a>
</li>
<li> remove the copy constructor declaration from 26.3.8.1 <a href="lib-numerics.html#lib.mask.array.cons"> [lib.mask.array.cons]</a>
</li>
<li> change paragraph 1 of 26.3.8.1 <a href="lib-numerics.html#lib.mask.array.cons"> [lib.mask.array.cons]</a> to read &quot;This constructor is declared
to be private. This constructor need not be defined.&quot;</li>
<li> remove the first sentence of paragraph 1 of 26.3.8.2 <a href="lib-numerics.html#lib.mask.array.assign"> [lib.mask.array.assign]</a>
</li>
<li> Change the first two words of the second sentence of paragraph 1 of
26.3.8.2 <a href="lib-numerics.html#lib.mask.array.assign"> [lib.mask.array.assign]</a> to &quot;This function.&quot;</li>
</ul>
<p>indirect_array:</p>
<ul>
<li>remove the copy constructor and copy-assignment operator declarations
from the indirect_array class definition in 26.3.9 <a href="lib-numerics.html#lib.template.indirect.array"> [lib.template.indirect.array]</a>
</li>
<li> remove the note in paragraph 2 of 26.3.9 <a href="lib-numerics.html#lib.template.indirect.array"> [lib.template.indirect.array]</a>
</li>
<li> remove the copy constructor declaration from 26.3.9.1 <a href="lib-numerics.html#lib.indirect.array.cons"> [lib.indirect.array.cons]</a>
</li>
<li> change the descriptive text in 26.3.9.1 <a href="lib-numerics.html#lib.indirect.array.cons"> [lib.indirect.array.cons]</a> to read &quot;This constructor is
declared to be private. This constructor need not be defined.&quot;</li>
<li> remove the first sentence of paragraph 1 of 26.3.9.2 <a href="lib-numerics.html#lib.indirect.array.assign"> [lib.indirect.array.assign]</a>
</li>
<li> Change the first two words of the second sentence of paragraph 1 of
26.3.9.2 <a href="lib-numerics.html#lib.indirect.array.assign"> [lib.indirect.array.assign]</a> to &quot;This function.&quot;</li>
</ul>
<p><i>[This wording is taken from Robert Klarer's reflector message,
c++std-lib-7827. Gabriel Dos Reis agrees that this general solution
is correct.]</i></p>
<p><b>Rationale:</b></p>
<p>Keeping the valarray constructors private is untenable. Merely
making valarray a friend of the helper classes isn't good enough,
because access to the copy constructor is checked in the user's
environment.</p>
<p>Making the assignment operator public is not strictly necessary to
solve this problem. A majority of the LWG <i>(straw poll: 13-4)</i>
believed we should make the assignment operators public, in addition
to the copy constructors, for reasons of symmetry and user
expectation.</p>
<hr>
<a name="254"><h3>254.&nbsp;Exception types in clause 19 are constructed from <tt>std::string</tt>
</h3></a><p>
<b>Section:</b>&nbsp;19.1 <a href="lib-diagnostics.html#lib.std.exceptions"> [lib.std.exceptions]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Dave Abrahams&nbsp; <b>Date:</b>&nbsp;01 Aug 2000</p>
<p>
Many of the standard exception types which implementations are
required to throw are constructed with a const std::string&amp;
parameter. For example:
</p>
<pre>
19.1.5 Class out_of_range [lib.out.of.range]
namespace std {
class out_of_range : public logic_error {
public:
explicit out_of_range(const string&amp; what_arg);
};
}
1 The class out_of_range defines the type of objects thrown as excep-
tions to report an argument value not in its expected range.
out_of_range(const string&amp; what_arg);
Effects:
Constructs an object of class out_of_range.
Postcondition:
strcmp(what(), what_arg.c_str()) == 0.
</pre>
<p>
There are at least two problems with this:
</p>
<ol>
<li>A program which is low on memory may end up throwing
std::bad_alloc instead of out_of_range because memory runs out while
constructing the exception object.</li>
<li>An obvious implementation which stores a std::string data member
may end up invoking terminate() during exception unwinding because the
exception object allocates memory (or rather fails to) as it is being
copied.</li>
</ol>
<p>
There may be no cure for (1) other than changing the interface to
out_of_range, though one could reasonably argue that (1) is not a
defect. Personally I don't care that much if out-of-memory is reported
when I only have 20 bytes left, in the case when out_of_range would
have been reported. People who use exception-specifications might care
a lot, though.
</p>
<p>
There is a cure for (2), but it isn't completely obvious. I think a
note for implementors should be made in the standard. Avoiding
possible termination in this case shouldn't be left up to chance. The
cure is to use a reference-counted &quot;string&quot; implementation
in the exception object. I am not necessarily referring to a
std::string here; any simple reference-counting scheme for a NTBS
would do.
</p>
<p><b>Further discussion, in email:</b></p>
<p>
...I'm not so concerned about (1). After all, a library implementation
can add const char* constructors as an extension, and users don't
<i>need</i> to avail themselves of the standard exceptions, though this is
a lame position to be forced into. FWIW, std::exception and
std::bad_alloc don't require a temporary basic_string.
</p>
<p>
...I don't think the fixed-size buffer is a solution to the problem,
strictly speaking, because you can't satisfy the postcondition
<br>
<tt>&nbsp;&nbsp;strcmp(what(), what_arg.c_str()) == 0</tt>
<br>
For all values of what_arg (i.e. very long values). That means that
the only truly conforming solution requires a dynamic allocation.
</p>
<p><b>Further discussion, from Redmond:</b></p>
<p>The most important progress we made at the Redmond meeting was
realizing that there are two separable issues here: the const
string&amp; constructor, and the copy constructor. If a user writes
something like <tt>throw std::out_of_range(&quot;foo&quot;)</tt>, the const
string&amp; constructor is invoked before anything gets thrown. The
copy constructor is potentially invoked during stack unwinding.</p>
<p>The copy constructor is a more serious problem, becuase failure
during stack unwinding invokes <tt>terminate</tt>. The copy
constructor must be nothrow.</p>
<p>The fundamental problem is that it's difficult to get the nothrow
requirement to work well with the requirement that the exception
objects store a string of unbounded size, particularly if you also try
to make the const string&amp; constructor nothrow. Options discussed
include:</p>
<ul>
<li>Limit the size of a string that exception objects are required to
throw: change the postconditions of 19.1.2 <a href="lib-diagnostics.html#lib.domain.error"> [lib.domain.error]</a> paragraph 3
and 19.1.6 <a href="lib-diagnostics.html#lib.runtime.error"> [lib.runtime.error]</a> paragraph 3 to something like this:
&quot;strncmp(what(), what_arg._str(), N) == 0, where N is an
implementation defined constant no smaller than 256&quot;.</li>
<li>Allow the const string&amp; constructor to throw, but not the
copy constructor. It's the implementor's responsibility to get it
right. (An implementor might use a simple refcount class.)</li>
<li>Compromise between the two: an implementation is not allowed to
throw if the string's length is less than some N, but, if it doesn't
throw, the string must compare equal to the argument.</li>
<li>Add a new constructor that takes a const char*</li>
</ul>
<p>(Not all of these options are mutually exclusive.)</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Toronto: some LWG members thought this was merely a QoI issue,
but most believed that it was at least a borderline defect. There was
more support for nonnormative advice to implementors than for a
normative change.]</i></p>
<p><i>[Redmond: discussed, without definite conclusion. Most LWG
members thought there was a real defect lurking here. A small group
(Herb, Kevlin, Howard, Martin, Dave) will try to make a
recommendation.]</i></p>
<hr>
<a name="258"><h3>258.&nbsp;Missing allocator requirement</h3></a><p>
<b>Section:</b>&nbsp;20.1.5 <a href="lib-utilities.html#lib.allocator.requirements"> [lib.allocator.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;22 Aug 2000</p>
<p>
From lib-7752:
</p>
<p>
I've been assuming (and probably everyone else has been assuming) that
allocator instances have a particular property, and I don't think that
property can be deduced from anything in Table 32.
</p>
<p>
I think we have to assume that allocator type conversion is a
homomorphism. That is, if x1 and x2 are of type X, where
X::value_type is T, and if type Y is X::template
rebind&lt;U&gt;::other, then Y(x1) == Y(x2) if and only if x1 == x2.
</p>
<p>
Further discussion: Howard Hinnant writes, in lib-7757:
</p>
<p>
I think I can prove that this is not provable by Table 32. And I agree
it needs to be true except for the &quot;and only if&quot;. If x1 != x2, I see no
reason why it can't be true that Y(x1) == Y(x2). Admittedly I can't
think of a practical instance where this would happen, or be valuable.
But I also don't see a need to add that extra restriction. I think we
only need:
</p>
<blockquote>
if (x1 == x2) then Y(x1) == Y(x2)
</blockquote>
<p>
If we decide that == on allocators is transitive, then I think I can
prove the above. But I don't think == is necessarily transitive on
allocators. That is:
</p>
<p>
Given x1 == x2 and x2 == x3, this does not mean x1 == x3.
</p>
<p>Example:</p>
<blockquote>
<p>
x1 can deallocate pointers from: x1, x2, x3 <br>
x2 can deallocate pointers from: x1, x2, x4 <br>
x3 can deallocate pointers from: x1, x3 <br>
x4 can deallocate pointers from: x2, x4
</p>
<p>
x1 == x2, and x2 == x4, but x1 != x4
</p>
</blockquote>
<p><b>Proposed resolution:</b></p>
<p><i>[Toronto: LWG members offered multiple opinions. One
opinion is that it should not be required that <tt>x1 == x2</tt>
implies <tt>Y(x1) == Y(x2)</tt>, and that it should not even be
required that <tt>X(x1) == x1</tt>. Another opinion is that
the second line from the bottom in table 32 already implies the
desired property. This issue should be considered in light of
other issues related to allocator instances.]</i></p>
<hr>
<a name="270"><h3>270.&nbsp;Binary search requirements overly strict</h3></a><p>
<b>Section:</b>&nbsp;25.3.3 <a href="lib-algorithms.html#lib.alg.binary.search"> [lib.alg.binary.search]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;18 Oct 2000</p>
<p>
Each of the four binary search algorithms (lower_bound, upper_bound,
equal_range, binary_search) has a form that allows the user to pass a
comparison function object. According to 25.3, paragraph 2, that
comparison function object has to be a strict weak ordering.
</p>
<p>
This requirement is slightly too strict. Suppose we are searching
through a sequence containing objects of type X, where X is some
large record with an integer key. We might reasonably want to look
up a record by key, in which case we would want to write something
like this:
</p>
<pre>
struct key_comp {
bool operator()(const X&amp; x, int n) const {
return x.key() &lt; n;
}
}
std::lower_bound(first, last, 47, key_comp());
</pre>
<p>
key_comp is not a strict weak ordering, but there is no reason to
prohibit its use in lower_bound.
</p>
<p>
There's no difficulty in implementing lower_bound so that it allows
the use of something like key_comp. (It will probably work unless an
implementor takes special pains to forbid it.) What's difficult is
formulating language in the standard to specify what kind of
comparison function is acceptable. We need a notion that's slightly
more general than that of a strict weak ordering, one that can encompass
a comparison function that involves different types. Expressing that
notion may be complicated.
</p>
<p><i>Additional questions raised at the Toronto meeting:</i></p>
<ul>
<li> Do we really want to specify what ordering the implementor must
use when calling the function object? The standard gives
specific expressions when describing these algorithms, but it also
says that other expressions (with different argument order) are
equivalent.</li>
<li> If we are specifying ordering, note that the standard uses both
orderings when describing <tt>equal_range</tt>.</li>
<li> Are we talking about requiring these algorithms to work properly
when passed a binary function object whose two argument types
are not the same, or are we talking about requirements when
they are passed a binary function object with several overloaded
versions of <tt>operator()</tt>?</li>
<li> The definition of a strict weak ordering does not appear to give
any guidance on issues of overloading; it only discusses expressions,
and all of the values in these expressions are of the same type.
Some clarification would seem to be in order.</li>
</ul>
<p><i>Additional discussion from Copenhagen:</i></p>
<ul>
<li>It was generally agreed that there is a real defect here: if
the predicate is merely required to be a Strict Weak Ordering, then
it's possible to pass in a function object with an overloaded
operator(), where the version that's actually called does something
completely inappropriate. (Such as returning a random value.)</li>
<li>An alternative formulation was presented in a paper distributed by
David Abrahams at the meeting, &quot;Binary Search with Heterogeneous
Comparison&quot;, J16-01/0027 = WG21 N1313: Instead of viewing the
predicate as a Strict Weak Ordering acting on a sorted sequence, view
the predicate/value pair as something that partitions a sequence.
This is almost equivalent to saying that we should view binary search
as if we are given a unary predicate and a sequence, such that f(*p)
is true for all p below a specific point and false for all p above it.
The proposed resolution is based on that alternative formulation.</li>
</ul>
<p><b>Proposed resolution:</b></p>
<p>Change 25.3 [lib.alg.sorting] paragraph 3 from:</p>
<blockquote>
3 For all algorithms that take Compare, there is a version that uses
operator&lt; instead. That is, comp(*i, *j) != false defaults to *i &lt;
*j != false. For the algorithms to work correctly, comp has to
induce a strict weak ordering on the values.
</blockquote>
<p>to:</p>
<blockquote>
3 For all algorithms that take Compare, there is a version that uses
operator&lt; instead. That is, comp(*i, *j) != false defaults to *i
&lt; *j != false. For algorithms other than those described in
lib.alg.binary.search (25.3.3) to work correctly, comp has to induce
a strict weak ordering on the values.
</blockquote>
<p>Add the following paragraph after 25.3 [lib.alg.sorting] paragraph 5:</p>
<blockquote>
-6- A sequence [start, finish) is partitioned with respect to an
expression f(e) if there exists an integer n such that
for all 0 &lt;= i &lt; distance(start, finish), f(*(begin+i)) is true if
and only if i &lt; n.
</blockquote>
<p>Change 25.3.3 [lib.alg.binary.search] paragraph 1 from:</p>
<blockquote>
-1- All of the algorithms in this section are versions of binary
search and assume that the sequence being searched is in order
according to the implied or explicit comparison function. They work
on non-random access iterators minimizing the number of
comparisons, which will be logarithmic for all types of
iterators. They are especially appropriate for random access
iterators, because these algorithms do a logarithmic number of
steps through the data structure. For non-random access iterators
they execute a linear number of steps.
</blockquote>
<p>to:</p>
<blockquote>
-1- All of the algorithms in this section are versions of binary
search and assume that the sequence being searched is partitioned
with respect to an expression formed by binding the search key to
an argument of the implied or explicit comparison function. They
work on non-random access iterators minimizing the number of
comparisons, which will be logarithmic for all types of
iterators. They are especially appropriate for random access
iterators, because these algorithms do a logarithmic number of
steps through the data structure. For non-random access iterators
they execute a linear number of steps.
</blockquote>
<p>Change 25.3.3.1 [lib.lower.bound] paragraph 1 from:</p>
<blockquote>
-1- Requires: Type T is LessThanComparable
(lib.lessthancomparable).
</blockquote>
<p>to:</p>
<blockquote>
-1- Requires: The elements e of [first, last) are partitioned with
respect to the expression e &lt; value or comp(e, value)
</blockquote>
<p>Remove 25.3.3.1 [lib.lower.bound] paragraph 2:</p>
<blockquote>
-2- Effects: Finds the first position into which value can be
inserted without violating the ordering.
</blockquote>
<p>Change 25.3.3.2 [lib.upper.bound] paragraph 1 from:</p>
<blockquote>
-1- Requires: Type T is LessThanComparable (lib.lessthancomparable).
</blockquote>
<p>to:</p>
<blockquote>
-1- Requires: The elements e of [first, last) are partitioned with
respect to the expression !(value &lt; e) or !comp(value, e)
</blockquote>
<p>Remove 25.3.3.2 [lib.upper.bound] paragraph 2:</p>
<blockquote>
-2- Effects: Finds the furthermost position into which value can be
inserted without violating the ordering.
</blockquote>
<p>Change 25.3.3.3 [lib.equal.range] paragraph 1 from:</p>
<blockquote>
-1- Requires: Type T is LessThanComparable
(lib.lessthancomparable).
</blockquote>
<p>to:</p>
<blockquote>
-1- Requires: The elements e of [first, last) are partitioned with
respect to the expressions e &lt; value and !(value &lt; e) or
comp(e, value) and !comp(value, e). Also, for all elements e of
[first, last), e &lt; value implies !(value &lt; e) or comp(e,
value) implies !comp(value, e)
</blockquote>
<p>Change 25.3.3.3 [lib.equal.range] paragraph 2 from:</p>
<blockquote>
-2- Effects: Finds the largest subrange [i, j) such that the value
can be inserted at any iterator k in it without violating the
ordering. k satisfies the corresponding conditions: !(*k &lt; value)
&amp;&amp; !(value &lt; *k) or comp(*k, value) == false &amp;&amp; comp(value, *k) ==
false.
</blockquote>
<p>to:</p>
<pre>
-2- Returns:
make_pair(lower_bound(first, last, value),
upper_bound(first, last, value))
or
make_pair(lower_bound(first, last, value, comp),
upper_bound(first, last, value, comp))
</pre>
<p>Change 25.3.3.3 [lib.binary.search] paragraph 1 from:</p>
<blockquote>
-1- Requires: Type T is LessThanComparable
(lib.lessthancomparable).
</blockquote>
<p>to:</p>
<blockquote>
-1- Requires: The elements e of [first, last) are partitioned with
respect to the expressions e &lt; value and !(value &lt; e) or comp(e,
value) and !comp(value, e). Also, for all elements e of [first,
last), e &lt; value implies !(value &lt; e) or comp(e, value) implies
!comp(value, e)
</blockquote>
<p><i>[Copenhagen: Dave Abrahams provided this wording]</i></p>
<p><i>[Redmond: Minor changes in wording. (Removed &quot;non-negative&quot;, and
changed the &quot;other than those described in&quot; wording.) Also, the LWG
decided to accept the &quot;optional&quot; part.]</i></p>
<p><b>Rationale:</b></p>
<p>The proposed resolution reinterprets binary search. Instead of
thinking about searching for a value in a sorted range, we view that
as an important special case of a more general algorithm: searching
for the partition point in a partitioned range.</p>
<p>We also add a guarantee that the old wording did not: we ensure
that the upper bound is no earlier than the lower bound, that
the pair returned by equal_range is a valid range, and that the first
part of that pair is the lower bound.</p>
<hr>
<a name="274"><h3>274.&nbsp;a missing/impossible allocator requirement</h3></a><p>
<b>Section:</b>&nbsp;20.1.5 <a href="lib-utilities.html#lib.allocator.requirements"> [lib.allocator.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;02 Nov 2000</p>
<p>
I see that table 31 in 20.1.5, p3 allows T in std::allocator&lt;T&gt; to be of
any type. But the synopsis in 20.4.1 calls for allocator&lt;&gt;::address() to
be overloaded on reference and const_reference, which is ill-formed for
all T = const U. In other words, this won't work:
</p>
<p>
template class std::allocator&lt;const int&gt;;
</p>
<p>
The obvious solution is to disallow specializations of allocators on
const types. However, while containers' elements are required to be
assignable (which rules out specializations on const T's), I think that
allocators might perhaps be potentially useful for const values in other
contexts. So if allocators are to allow const types a partial
specialization of std::allocator&lt;const T&gt; would probably have to be
provided.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change the text in row 1, column 2 of table 32 in 20.1.5, p3 from</p>
<blockquote>
any type
</blockquote>
<p>to</p>
<blockquote>
any non-const, non-reference type
</blockquote>
<p><i>[Redmond: previous proposed resolution was &quot;any non-const,
non-volatile, non-reference type&quot;. Got rid of the &quot;non-volatile&quot;.]</i></p>
<p><b>Rationale:</b></p>
<p>
Two resolutions were originally proposed: one that partially
specialized std::allocator for const types, and one that said an
allocator's value type may not be const. The LWG chose the second.
The first wouldn't be appropriate, because allocators are intended for
use by containers, and const value types don't work in containers.
Encouraging the use of allocators with const value types would only
lead to unsafe code.
</p>
<p>
The original text for proposed resolution 2 was modified so that it
also forbids volatile types and reference types.
</p>
<hr>
<a name="276"><h3>276.&nbsp;Assignable requirement for container value type overly strict</h3></a><p>
<b>Section:</b>&nbsp;23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Peter Dimov&nbsp; <b>Date:</b>&nbsp;07 Nov 2000</p>
<p>
23.1/3 states that the objects stored in a container must be
Assignable. 23.3.1 <a href="lib-containers.html#lib.map"> [lib.map]</a>, paragraph 2,
states that map satisfies all requirements for a container, while in
the same time defining value_type as pair&lt;const Key, T&gt; - a type
that is not Assignable.
</p>
<p>
It should be noted that there exists a valid and non-contradictory
interpretation of the current text. The wording in 23.1/3 avoids
mentioning value_type, referring instead to &quot;objects stored in a
container.&quot; One might argue that map does not store objects of
type map::value_type, but of map::mapped_type instead, and that the
Assignable requirement applies to map::mapped_type, not
map::value_type.
</p>
<p>
However, this makes map a special case (other containers store objects of
type value_type) and the Assignable requirement is needlessly restrictive in
general.
</p>
<p>
For example, the proposed resolution of active library issue
<a href="lwg-defects.html#103">103</a> is to make set::iterator a constant iterator; this
means that no set operations can exploit the fact that the stored
objects are Assignable.
</p>
<p>
This is related to, but slightly broader than, closed issue
<a href="lwg-closed.html#140">140</a>.
</p>
<p><b>Proposed resolution:</b></p>
<p>23.1/3: Strike the trailing part of the sentence:</p>
<blockquote>
, and the additional requirements of Assignable types from 23.1/3
</blockquote>
<p>so that it reads:</p>
<blockquote>
-3- The type of objects stored in these components must meet the
requirements of CopyConstructible types (lib.copyconstructible).
</blockquote>
<p>23.1/4: Modify to make clear that this requirement is not for all
containers. Change to:</p>
<blockquote>
-4- Table 64 defines the Assignable requirement. Some containers
require this property of the types to be stored in the container. T is
the type used to instantiate the container. t is a value of T, and u is
a value of (possibly const) T.
</blockquote>
<p>23.1, Table 65: in the first row, change &quot;T is Assignable&quot; to &quot;T is
CopyConstructible&quot;.</p>
<p>23.2.1/2: Add sentence for Assignable requirement. Change to:</p>
<blockquote>
-2- A deque satisfies all of the requirements of a container and of a
reversible container (given in tables in lib.container.requirements) and
of a sequence, including the optional sequence requirements
(lib.sequence.reqmts). In addition to the requirements on the stored
object described in 23.1[lib.container.requirements], the stored object
must also meet the requirements of Assignable. Descriptions are
provided here only for operations on deque that are not described in one
of these tables or for operations where there is additional semantic
information.
</blockquote>
<p>23.2.2/2: Add Assignable requirement to specific methods of list.
Change to:</p>
<blockquote>
<p>-2- A list satisfies all of the requirements of a container and of a
reversible container (given in two tables in lib.container.requirements)
and of a sequence, including most of the the optional sequence
requirements (lib.sequence.reqmts). The exceptions are the operator[]
and at member functions, which are not provided.
[Footnote: These member functions are only provided by containers whose
iterators are random access iterators. --- end foonote]
</p>
<p>list does not require the stored type T to be Assignable unless the
following methods are instantiated:
[Footnote: Implementors are permitted but not required to take advantage
of T's Assignable properties for these methods. -- end foonote]
</p>
<pre>
list&lt;T,Allocator&gt;&amp; operator=(const list&lt;T,Allocator&gt;&amp; x );
template &lt;class InputIterator&gt;
void assign(InputIterator first, InputIterator last);
void assign(size_type n, const T&amp; t);
</pre>
<p>Descriptions are provided here only for operations on list that are not
described in one of these tables or for operations where there is
additional semantic information.</p>
</blockquote>
<p>23.2.4/2: Add sentence for Assignable requirement. Change to:</p>
<blockquote>
-2- A vector satisfies all of the requirements of a container and of a
reversible container (given in two tables in lib.container.requirements)
and of a sequence, including most of the optional sequence requirements
(lib.sequence.reqmts). The exceptions are the push_front and pop_front
member functions, which are not provided. In addition to the
requirements on the stored object described in
23.1[lib.container.requirements], the stored object must also meet the
requirements of Assignable. Descriptions are provided here only for
operations on vector that are not described in one of these tables or
for operations where there is additional semantic information.
</blockquote>
<p><b>Rationale:</b></p>
<p>list, set, multiset, map, multimap are able to store non-Assignables.
However, there is some concern about <tt>list&lt;T&gt;</tt>:
although in general there's no reason for T to be Assignable, some
implementations of the member functions <tt>operator=</tt> and
<tt>assign</tt> do rely on that requirement. The LWG does not want
to forbid such implementations.</p>
<p>Note that the type stored in a standard container must still satisfy
the requirements of the container's allocator; this rules out, for
example, such types as &quot;const int&quot;. See issue <a href="lwg-active.html#274">274</a>
for more details.
</p>
<p>In principle we could also relax the &quot;Assignable&quot; requirement for
individual <tt>vector</tt> member functions, such as
<tt>push_back</tt>. However, the LWG did not see great value in such
selective relaxation. Doing so would remove implementors' freedom to
implement <tt>vector::push_back</tt> in terms of
<tt>vector::insert</tt>.</p>
<hr>
<a name="278"><h3>278.&nbsp;What does iterator validity mean?</h3></a><p>
<b>Section:</b>&nbsp;23.2.2.4 <a href="lib-containers.html#lib.list.ops"> [lib.list.ops]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;P.J. Plauger&nbsp; <b>Date:</b>&nbsp;27 Nov 2000</p>
<p>
Section 23.2.2.4 [lib.list.ops] states that
</p>
<pre>
void splice(iterator position, list&lt;T, Allocator&gt;&amp; x);
</pre>
<p>
<i>invalidates</i> all iterators and references to list <tt>x</tt>.
</p>
<p>
But what does the C++ Standard mean by &quot;invalidate&quot;? You
can still dereference the iterator to a spliced list element, but
you'd better not use it to delimit a range within the original
list. For the latter operation, it has definitely lost some of its
validity.
</p>
<p>
If we accept the proposed resolution to issue <a href="lwg-defects.html#250">250</a>,
then we'd better clarify that a &quot;valid&quot; iterator need no
longer designate an element within the same container as it once did.
We then have to clarify what we mean by invalidating a past-the-end
iterator, as when a vector or string grows by reallocation. Clearly,
such an iterator has a different kind of validity. Perhaps we should
introduce separate terms for the two kinds of &quot;validity.&quot;
</p>
<p><b>Proposed resolution:</b></p>
<p>Add the following text to the end of section 24.1 <a href="lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>,
after paragraph 5:</p>
<blockquote>
An <i>invalid</i> iterator is an iterator that may be
singular. [Footnote: This definition applies to pointers, since
pointers are iterators. The effect of dereferencing an iterator that
has been invalidated is undefined.]
</blockquote>
<p><i>[post-Copenhagen: Matt provided wording.]</i></p>
<p><i>[Redmond: General agreement with the intent, some objections to
the wording. Dave provided new wording.]</i></p>
<hr>
<a name="280"><h3>280.&nbsp;Comparison of reverse_iterator to const reverse_iterator</h3></a><p>
<b>Section:</b>&nbsp;24.4.1 <a href="lib-iterators.html#lib.reverse.iterators"> [lib.reverse.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Steve Cleary&nbsp; <b>Date:</b>&nbsp;27 Nov 2000</p>
<p>
This came from an email from Steve Cleary to Fergus in reference to
issue <a href="lwg-active.html#179">179</a>. The library working group briefly discussed
this in Toronto and believed it should be a separate issue. There was
also some reservations about whether this was a worthwhile problem to
fix.
</p>
<p>
Steve said: &quot;Fixing reverse_iterator. std::reverse_iterator can
(and should) be changed to preserve these additional
requirements.&quot; He also said in email that it can be done without
breaking user's code: &quot;If you take a look at my suggested
solution, reverse_iterator doesn't have to take two parameters; there
is no danger of breaking existing code, except someone taking the
address of one of the reverse_iterator global operator functions, and
I have to doubt if anyone has ever done that. . . <i>But</i>, just in
case they have, you can leave the old global functions in as well --
they won't interfere with the two-template-argument functions. With
that, I don't see how <i>any</i> user code could break.&quot;
</p>
<p><b>Proposed resolution:</b></p>
<p>
<b>Section:</b> 24.4.1.1 <a href="lib-iterators.html#lib.reverse.iterator"> [lib.reverse.iterator]</a>
add/change the following declarations:</p>
<pre>
A) Add a templated assignment operator, after the same manner
as the templated copy constructor, i.e.:
template &lt; class U &gt;
reverse_iterator &lt; Iterator &gt;&amp; operator=(const reverse_iterator&lt; U &gt;&amp; u);
B) Make all global functions (except the operator+) have
two template parameters instead of one, that is, for
operator ==, !=, &lt;, &gt;, &lt;=, &gt;=, - replace:
template &lt; class Iterator &gt;
typename reverse_iterator&lt; Iterator &gt;::difference_type operator-(
const reverse_iterator&lt; Iterator &gt;&amp; x,
const reverse_iterator&lt; Iterator &gt;&amp; y);
with:
template &lt; class Iterator1, class Iterator2 &gt;
typename reverse_iterator &lt; Iterator1 &gt;::difference_type operator-(
const reverse_iterator &lt; Iterator1 &gt; &amp; x,
const reverse_iterator &lt; Iterator2 &gt; &amp; y);
</pre>
<p>
Also make the addition/changes for these signatures in
24.4.1.3 <a href="lib-iterators.html#lib.reverse.iter.ops"> [lib.reverse.iter.ops]</a>.
</p>
<p><i>[
Copenhagen: The LWG is concerned that the proposed resolution
introduces new overloads. Experience shows that introducing
overloads is always risky, and that it would be inappropriate to
make this change without implementation experience. It may be
desirable to provide this feature in a different way.
]</i></p>
<hr>
<a name="282"><h3>282.&nbsp;What types does numpunct grouping refer to?</h3></a><p>
<b>Section:</b>&nbsp;22.2.2.2.2 <a href="lib-locales.html#lib.facet.num.put.virtuals"> [lib.facet.num.put.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;5 Dec 2000</p>
<p>
Paragraph 16 mistakenly singles out integral types for inserting
thousands_sep() characters. This conflicts with the syntax for floating
point numbers described under 22.2.3.1/2.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change paragraph 16 from:</p>
<blockquote>
For integral types, punct.thousands_sep() characters are inserted into
the sequence as determined by the value returned by punct.do_grouping()
using the method described in 22.2.3.1.2 <a href="lib-locales.html#lib.facet.numpunct.virtuals"> [lib.facet.numpunct.virtuals]</a>.
</blockquote>
<p>To:</p>
<blockquote>
For arithmetic types, punct.thousands_sep() characters are inserted into
the sequence as determined by the value returned by punct.do_grouping()
using the method described in 22.2.3.1.2 <a href="lib-locales.html#lib.facet.numpunct.virtuals"> [lib.facet.numpunct.virtuals]</a>.
</blockquote>
<p><i>[
Copenhagen: Opinions were divided about whether this is actually an
inconsistency, but at best it seems to have been unintentional. This
is only an issue for floating-point output: The standard is
unambiguous that implementations must parse thousands_sep characters
when performing floating-point. The standard is also unambiguous that
this requirement does not apply to the &quot;C&quot; locale.
]</i></p>
<p><i>[
A survey of existing practice is needed; it is believed that some
implementations do insert thousands_sep characters for floating-point
output and others fail to insert thousands_sep characters for
floating-point input even though this is unambiguously required by the
standard.
]</i></p>
<hr>
<a name="283"><h3>283.&nbsp;std::replace() requirement incorrect/insufficient</h3></a><p>
<b>Section:</b>&nbsp;25.2.4 <a href="lib-algorithms.html#lib.alg.replace"> [lib.alg.replace]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;15 Dec 2000</p>
<p>
The requirements in 25.2.4 <a href="lib-algorithms.html#lib.alg.replace"> [lib.alg.replace]</a>, p1 that <tt>T</tt> to be
<tt>Assignable</tt> (23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>) is not necessary or
sufficient for either of the algorithms. The algorithms require that
<tt>std::iterator_traits&lt;ForwardIterator&gt;::value_type</tt> be
<tt>Assignable</tt> and that both
<tt>std::iterator_traits&lt;ForwardIterator&gt;::value_type</tt> and be
<tt>EqualityComparable</tt> (20.1.1 <a href="lib-utilities.html#lib.equalitycomparable"> [lib.equalitycomparable]</a>) with respect to
one another.
</p>
<p>
<b>Further discussion, from Jeremy</b>:
</p>
<p>There are a number of problems with the requires clauses for the
algorithms in 25.1 <a href="lib-algorithms.html#lib.alg.nonmodifying"> [lib.alg.nonmodifying]</a> and 25.2 <a href="lib-algorithms.html#lib.alg.modifying.operations"> [lib.alg.modifying.operations]</a>. The requires
clause of each algorithm should describe the necessary and sufficient
requirements on the inputs to the algorithm such that the algorithm
compiles and runs properly. Many of the requires clauses fail to do
this. Here is a summary of the kinds of mistakes:</p>
<ol>
<li> Use of EqualityComparable, which only puts requirements on a single
type, when in fact an equality operator is required between two
different types, typically either T and the iterators value_type
or between the value_type's of two different iterators.</li>
<li> Use of Assignable for T when in fact what was needed is Assignable
for the value_type of the iterator, and convertability from T to the
value_type of the iterator. Or for output iterators, the requirement
should be that T is writable to the iterator (output iterators do
not have value types; see issue <a href="lwg-active.html#324">324</a>).</li>
<li> Lack of a requires clause.</li>
</ol>
<p>Here is the list of algorithms that contain mistakes:</p>
<ul>
<li>25.1.2 <a href="lib-algorithms.html#lib.alg.find"> [lib.alg.find]</a>
</li>
<li>25.1.3 <a href="lib-algorithms.html#lib.alg.find.end"> [lib.alg.find.end]</a>
</li>
<li>25.1.4 <a href="lib-algorithms.html#lib.alg.find.first.of"> [lib.alg.find.first.of]</a>
</li>
<li>25.1.6 <a href="lib-algorithms.html#lib.alg.count"> [lib.alg.count]</a>
</li>
<li>25.1.7 <a href="lib-algorithms.html#lib.mismatch"> [lib.mismatch]</a>
</li>
<li>25.1.8 <a href="lib-algorithms.html#lib.alg.equal"> [lib.alg.equal]</a>
</li>
<li>25.1.9 <a href="lib-algorithms.html#lib.alg.search"> [lib.alg.search]</a>
</li>
<li>25.2.4 <a href="lib-algorithms.html#lib.alg.replace"> [lib.alg.replace]</a>
</li>
<li>25.2.5 <a href="lib-algorithms.html#lib.alg.fill"> [lib.alg.fill]</a>
</li>
<li>25.2.7 <a href="lib-algorithms.html#lib.alg.remove"> [lib.alg.remove]</a>
</li>
</ul>
<p>Also, in the requirements for EqualityComparable, the requirement that
the operator be defined for const objects is lacking.</p>
<p><b>Proposed resolution:</b></p>
<p>20.1.1 <a href="lib-utilities.html#lib.equalitycomparable"> [lib.equalitycomparable]</a> Change p1 from</p>
<blockquote>
In Table 28, T is a type to be supplied by a C++ program instantiating
a template, a, b, and c are values of type T.
</blockquote>
<p>to</p>
<blockquote>
In Table 28, T is a type to be supplied by a C++ program instantiating
a template, a, b, and c are values of type const T.
</blockquote>
<p>25.1.2 <a href="lib-algorithms.html#lib.alg.find"> [lib.alg.find]</a> Change p1 from</p>
<blockquote>
Requires: Type T is EqualityComparable (20.1.1).
</blockquote>
<p>to </p>
<blockquote>
Requires: There must be a equality operator defined that accepts type
std::iterator_traits&lt;InputIterator&gt;::reference for the left operand
and const T for the right operand.
</blockquote>
<p>25.1.3 <a href="lib-algorithms.html#lib.alg.find.end"> [lib.alg.find.end]</a> Add the following requires clause</p>
<blockquote>
Requires: There must be an equality operator defined that accepts
type const std::iterator_traits&lt;ForwardIterator1&gt;::value_type for the
left operand and const
std::iterator_traits&lt;ForwardIterator2&gt;::value_type for the right
operand.
</blockquote>
<p>25.1.4 <a href="lib-algorithms.html#lib.alg.find.first.of"> [lib.alg.find.first.of]</a> Add the following requires clause</p>
<blockquote>
Requires: There must be an equality operator defined that accepts
type const std::iterator_traits&lt;ForwardIterator1&gt;::value_type for the
left operand and const
std::iterator_traits&lt;ForwardIterator2&gt;::value_type for the right
operand.
</blockquote>
<p>25.1.5 <a href="lib-algorithms.html#lib.alg.adjacent.find"> [lib.alg.adjacent.find]</a> Add the following requires clause</p>
<blockquote>
Requires: T must be EqualityComparable (20.1.1).
</blockquote>
<p>25.1.6 <a href="lib-algorithms.html#lib.alg.count"> [lib.alg.count]</a> Change p1 from</p>
<blockquote>
Requires: Type T is EqualityComparable (20.1.1).
</blockquote>
<p>to</p>
<blockquote>
Requires: There must be a equality operator defined that accepts type
std::iterator_traits&lt;InputIterator&gt;::reference for the left operand
and const T for the right operand.
</blockquote>
<p>25.1.7 <a href="lib-algorithms.html#lib.mismatch"> [lib.mismatch]</a> Add the following requires clause</p>
<blockquote>
Requires: There must be an equality operator defined that accepts type
std::iterator_traits&lt;InputIterator1&gt;::reference for the left operand
and std::iterator_traits&lt;InputIterator2&gt;::reference for the right operand.
</blockquote>
<p>25.1.8 <a href="lib-algorithms.html#lib.alg.equal"> [lib.alg.equal]</a> Add the following requires clause</p>
<blockquote>
Requires: There must be an equality operator defined that accepts type
std::iterator_traits&lt;InputIterator1&gt;::reference for the left operand
and std::iterator_traits&lt;InputIterator2&gt;::reference for the right operand.
</blockquote>
<p>25.1.9 <a href="lib-algorithms.html#lib.alg.search"> [lib.alg.search]</a> Add the following requires clause</p>
<blockquote>
Requires: There must be an equality operator defined that accepts
type const std::iterator_traits&lt;ForwardIterator1&gt;::value_type for
the left operand and const
std::iterator_traits&lt;ForwardIterator2&gt;::value_type for the right
operand.
</blockquote>
<p>Change change p4 from</p>
<blockquote>
Requires: Type T is EqualityComparable (20.1.1), type Size is
convertible to integral type (4.7.12.3).
</blockquote>
<p>to</p>
<blockquote>
Requires: There must be an equality operator defined that accepts
const std::iterator_traits&lt;ForwardIterator&gt;::value_type for the left
operand and const T for the right operand. The type Size is convertible to
integral type (4.7.12.3).
</blockquote>
<p>25.2.4 <a href="lib-algorithms.html#lib.alg.replace"> [lib.alg.replace]</a> Change p1 from</p>
<blockquote>
Requires: Type T is Assignable (23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>) (and, for replace(),
EqualityComparable (20.1.1 <a href="lib-utilities.html#lib.equalitycomparable"> [lib.equalitycomparable]</a>)).
</blockquote>
<p>to</p>
<blockquote>
Requires: Type std::iterator_traits&lt;ForwardIterator&gt;::value_type
is Assignable (23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>) and the type const T is convertible to
std::iterator_traits&lt;ForwardIterator&gt;::value_type. For replace(), an
equality operator must be defined that accepts type
std::iterator_traits&lt;ForwardIterator&gt;::reference for the left operand
and const T for the right operand.
</blockquote>
<p>and change p4 from</p>
<blockquote>
Requires: Type T is Assignable (23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>) (and, for replace_copy(),
EqualityComparable (20.1.1 <a href="lib-utilities.html#lib.equalitycomparable"> [lib.equalitycomparable]</a>)). The ranges [first, last) and [result,
result + (last - first)) shall not overlap.
</blockquote>
<p>to</p>
<blockquote>
Requires: Both types const T and
std::iterator_traits&lt;InputIterator&gt;::reference are writable to the
OutputIterator type. For replace_copy() an equality operator must be
defined that accepts type
std::iterator_traits&lt;InputIterator&gt;::reference for the left operand
and const T for the right operand. The ranges [first, last) and [result,
result + (last - first)) shall not overlap.
</blockquote>
<p>25.2.5 <a href="lib-algorithms.html#lib.alg.fill"> [lib.alg.fill]</a> Change p1 from</p>
<blockquote>
Requires: Type T is Assignable (23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a> ). Size is convertible to an integral
type (3.9.1 <a href="basic.html#basic.fundamental"> [basic.fundamental]</a> ).
</blockquote>
<p>to</p>
<blockquote>
Requires: Type const T is writable to the OutputIterator. Size is
convertible to an integral type (3.9.1 <a href="basic.html#basic.fundamental"> [basic.fundamental]</a> ).
</blockquote>
<p>25.2.7 <a href="lib-algorithms.html#lib.alg.remove"> [lib.alg.remove]</a> Change p1 from</p>
<blockquote>
Requires: Type T is EqualityComparable (20.1.1 <a href="lib-utilities.html#lib.equalitycomparable"> [lib.equalitycomparable]</a>).
</blockquote>
<p>to</p>
<blockquote>
Requires: There must be an equality operator defined that accepts
type const std::iterator_traits&lt;ForwardIterator&gt;::value_type for the left
operand and const T for the right operand. The type
std::iterator_traits&lt;ForwardIterator&gt;::value_type must be Assignable
(23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>).
</blockquote>
<hr>
<a name="284"><h3>284.&nbsp;unportable example in 20.3.7, p6</h3></a><p>
<b>Section:</b>&nbsp;20.3.7 <a href="lib-utilities.html#lib.function.pointer.adaptors"> [lib.function.pointer.adaptors]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;26 Dec 2000</p>
<p>The example in 20.3.7 <a href="lib-utilities.html#lib.function.pointer.adaptors"> [lib.function.pointer.adaptors]</a>, p6 shows how to use the C
library function <tt>strcmp()</tt> with the function pointer adapter
<tt>ptr_fun()</tt>. But since it's unspecified whether the C library
functions have <tt>extern &quot;C&quot;</tt> or <tt>extern
&quot;C++&quot;</tt> linkage [17.4.2.2 <a href="lib-intro.html#lib.using.linkage"> [lib.using.linkage]</a>], and since
function pointers with different the language linkage specifications
(7.5 <a href="dcl.html#dcl.link"> [dcl.link]</a>) are incompatible, whether this example is
well-formed is unspecified.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change 20.3.7 <a href="lib-utilities.html#lib.function.pointer.adaptors"> [lib.function.pointer.adaptors]</a> paragraph 6 from:</p>
<blockquote>
<p>[<i>Example:</i>
</p>
<pre>
replace_if(v.begin(), v.end(), not1(bind2nd(ptr_fun(strcmp), &quot;C&quot;)), &quot;C++&quot;);
</pre>
<p>replaces each <tt>C</tt> with <tt>C++</tt> in sequence <tt>v</tt>.</p>
</blockquote>
<p>to:</p>
<blockquote>
<p>[<i>Example:</i>
</p>
<pre>
int compare(const char*, const char*);
replace_if(v.begin(), v.end(),
not1(bind2nd(ptr_fun(compare), &quot;abc&quot;)), &quot;def&quot;);
</pre>
<p>replaces each <tt>abc</tt> with <tt>def</tt> in sequence <tt>v</tt>.</p>
</blockquote>
<p>Also, remove footnote 215 in that same paragraph.</p>
<p><i>[Copenhagen: Minor change in the proposed resolution. Since this
issue deals in part with C and C++ linkage, it was believed to be too
confusing for the strings in the example to be &quot;C&quot; and &quot;C++&quot;.
]</i></p>
<p><i>[Redmond: More minor changes. Got rid of the footnote (which
seems to make a sweeping normative requirement, even though footnotes
aren't normative), and changed the sentence after the footnote so that
it corresponds to the new code fragment.]</i></p>
<hr>
<a name="290"><h3>290.&nbsp;Requirements to for_each and its function object</h3></a><p>
<b>Section:</b>&nbsp;25.1.1 <a href="lib-algorithms.html#lib.alg.foreach"> [lib.alg.foreach]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Angelika Langer&nbsp; <b>Date:</b>&nbsp;03 Jan 2001</p>
<p>The specification of the for_each algorithm does not have a
&quot;Requires&quot; section, which means that there are no
restrictions imposed on the function object whatsoever. In essence it
means that I can provide any function object with arbitrary side
effects and I can still expect a predictable result. In particular I
can expect that the function object is applied exactly last - first
times, which is promised in the &quot;Complexity&quot; section.
</p>
<p>I don't see how any implementation can give such a guarantee
without imposing requirements on the function object.
</p>
<p>Just as an example: consider a function object that removes
elements from the input sequence. In that case, what does the
complexity guarantee (applies f exactly last - first times) mean?
</p>
<p>One can argue that this is obviously a nonsensical application and
a theoretical case, which unfortunately it isn't. I have seen
programmers shooting themselves in the foot this way, and they did not
understand that there are restrictions even if the description of the
algorithm does not say so.
</p>
<p><b>Proposed resolution:</b></p>
<p>Add a &quot;Requires&quot; section to section 25.1.1 similar to those
proposed for transform and the numeric algorithms (see issue
<a href="lwg-defects.html#242">242</a>):
</p>
<blockquote>
-2- <b>Requires</b>: In the range [first, last], f shall not invalidate
iterators or subranges.
</blockquote>
<p><i>[Copenhagen: The LWG agrees that a function object passed to an
algorithm should not invalidate iterators in the range that the
algorithm is operating on. The LWG believes that this should be a
blanket statement in Clause 25, not just a special requirement for
<tt>for_each</tt>.
]</i></p>
<hr>
<a name="291"><h3>291.&nbsp;Underspecification of set algorithms</h3></a><p>
<b>Section:</b>&nbsp;25.3.5 <a href="lib-algorithms.html#lib.alg.set.operations"> [lib.alg.set.operations]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;03 Jan 2001</p>
<p>
The standard library contains four algorithms that compute set
operations on sorted ranges: <tt>set_union</tt>, <tt>set_intersection</tt>,
<tt>set_difference</tt>, and <tt>set_symmetric_difference</tt>. Each
of these algorithms takes two sorted ranges as inputs, and writes the
output of the appropriate set operation to an output range. The elements
in the output range are sorted.
</p>
<p>
The ordinary mathematical definitions are generalized so that they
apply to ranges containing multiple copies of a given element. Two
elements are considered to be &quot;the same&quot; if, according to an
ordering relation provided by the user, neither one is less than the
other. So, for example, if one input range contains five copies of an
element and another contains three, the output range of <tt>set_union</tt>
will contain five copies, the output range of
<tt>set_intersection</tt> will contain three, the output range of
<tt>set_difference</tt> will contain two, and the output range of
<tt>set_symmetric_difference</tt> will contain two.
</p>
<p>
Because two elements can be &quot;the same&quot; for the purposes
of these set algorithms, without being identical in other respects
(consider, for example, strings under case-insensitive comparison),
this raises a number of unanswered questions:
</p>
<ul>
<li>If we're copying an element that's present in both of the
input ranges, which one do we copy it from?</li>
<li>If there are <i>n</i> copies of an element in the relevant
input range, and the output range will contain fewer copies (say
<i>m</i>) which ones do we choose? The first <i>m</i>, or the last
<i>m</i>, or something else?</li>
<li>Are these operations stable? That is, does a run of equivalent
elements appear in the output range in the same order as as it
appeared in the input range(s)?</li>
</ul>
<p>
The standard should either answer these questions, or explicitly
say that the answers are unspecified. I prefer the former option,
since, as far as I know, all existing implementations behave the
same way.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[The LWG agrees that the standard should answer these questions.
Matt will provide wording.]</i></p>
<hr>
<a name="294"><h3>294.&nbsp;User defined macros and standard headers</h3></a><p>
<b>Section:</b>&nbsp;17.4.3.1.1 <a href="lib-intro.html#lib.macro.names"> [lib.macro.names]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;James Kanze&nbsp; <b>Date:</b>&nbsp;11 Jan 2001</p>
<p>Paragraph 2 of 17.4.3.1.1 <a href="lib-intro.html#lib.macro.names"> [lib.macro.names]</a> reads: &quot;A
translation unit that includes a header shall not contain any macros
that define names declared in that header.&quot; As I read this, it
would mean that the following program is legal:</p>
<pre>
#define npos 3.14
#include &lt;sstream&gt;
</pre>
<p>since npos is not defined in &lt;sstream&gt;. It is, however, defined
in &lt;string&gt;, and it is hard to imagine an implementation in
which &lt;sstream&gt; didn't include &lt;string&gt;.</p>
<p>I think that this phrase was probably formulated before it was
decided that a standard header may freely include other standard
headers. The phrase would be perfectly appropriate for C, for
example. In light of 17.4.4.1 <a href="lib-intro.html#lib.res.on.headers"> [lib.res.on.headers]</a> paragraph 1, however,
it isn't stringent enough.</p>
<p><b>Proposed resolution:</b></p>
<p>In paragraph 2 of 17.4.3.1.1 <a href="lib-intro.html#lib.macro.names"> [lib.macro.names]</a>, change &quot;A
translation unit that includes a header shall not contain any macros
that define names declared in that header.&quot; to &quot;A
translation unit that includes a header shall not contain any macros
that define names declared in any standard header.&quot;</p>
<p><i>[Copenhagen: the general idea is clearly correct, but there is
concern about making sure that the two paragraphs in 17.4.3.1.1 <a href="lib-intro.html#lib.macro.names"> [lib.macro.names]</a> remain consistent. Nathan will provide new
wording.]</i></p>
<hr>
<a name="299"><h3>299.&nbsp;Incorrect return types for iterator dereference</h3></a><p>
<b>Section:</b>&nbsp;24.1.4 <a href="lib-iterators.html#lib.bidirectional.iterators"> [lib.bidirectional.iterators]</a>, 24.1.5 <a href="lib-iterators.html#lib.random.access.iterators"> [lib.random.access.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;John Potter&nbsp; <b>Date:</b>&nbsp;22 Jan 2001</p>
<p>
In section 24.1.4 <a href="lib-iterators.html#lib.bidirectional.iterators"> [lib.bidirectional.iterators]</a>,
Table 75 gives the return type of *r-- as convertible to T. This is
not consistent with Table 74 which gives the return type of *r++ as
T&amp;. *r++ = t is valid while *r-- = t is invalid.
</p>
<p>
In section 24.1.5 <a href="lib-iterators.html#lib.random.access.iterators"> [lib.random.access.iterators]</a>,
Table 76 gives the return type of a[n] as convertible to T. This is
not consistent with the semantics of *(a + n) which returns T&amp; by
Table 74. *(a + n) = t is valid while a[n] = t is invalid.
</p>
<p>
Discussion from the Copenhagen meeting: the first part is
uncontroversial. The second part, operator[] for Random Access
Iterators, requires more thought. There are reasonable arguments on
both sides. Return by value from operator[] enables some potentially
useful iterators, e.g. a random access &quot;iota iterator&quot; (a.k.a
&quot;counting iterator&quot; or &quot;int iterator&quot;). There isn't any obvious way
to do this with return-by-reference, since the reference would be to a
temporary. On the other hand, <tt>reverse_iterator</tt> takes an
arbitrary Random Access Iterator as template argument, and its
operator[] returns by reference. If we decided that the return type
in Table 76 was correct, we would have to change
<tt>reverse_iterator</tt>. This change would probably affect user
code.
</p>
<p>
History: the contradiction between <tt>reverse_iterator</tt> and the
Random Access Iterator requirements has been present from an early
stage. In both the STL proposal adopted by the committee
(N0527==94-0140) and the STL technical report (HPL-95-11 (R.1), by
Stepanov and Lee), the Random Access Iterator requirements say that
operator[]'s return value is &quot;convertible to T&quot;. In N0527
reverse_iterator's operator[] returns by value, but in HPL-95-11
(R.1), and in the STL implementation that HP released to the public,
reverse_iterator's operator[] returns by reference. In 1995, the
standard was amended to reflect the contents of HPL-95-11 (R.1). The
original intent for operator[] is unclear.
</p>
<p>
In the long term it may be desirable to add more fine-grained
iterator requirements, so that access method and traversal strategy
can be decoupled. (See &quot;Improved Iterator Categories and
Requirements&quot;, N1297 = 01-0011, by Jeremy Siek.) Any decisions
about issue 299 should keep this possibility in mind.
</p>
<p><b>Proposed resolution:</b></p>
<p>In section 24.1.4 <a href="lib-iterators.html#lib.bidirectional.iterators"> [lib.bidirectional.iterators]</a>, change the return type in table
75 from &quot;convertible to T&quot; to T&amp;.</p>
<p>In section 24.1.5 <a href="lib-iterators.html#lib.random.access.iterators"> [lib.random.access.iterators]</a>, change the return type in table
76 from &quot;convertible to T&quot; to T&amp;.</p>
<hr>
<a name="300"><h3>300.&nbsp;list::merge() specification incomplete</h3></a><p>
<b>Section:</b>&nbsp;23.2.2.4 <a href="lib-containers.html#lib.list.ops"> [lib.list.ops]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;John Pedretti&nbsp; <b>Date:</b>&nbsp;23 Jan 2001</p>
<p>
The &quot;Effects&quot; clause for list::merge() (23.2.2.4, p23)
appears to be incomplete: it doesn't cover the case where the argument
list is identical to *this (i.e., this == &amp;x). The requirement in the
note in p24 (below) is that x be empty after the merge which is surely
unintended in this case.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 23.2.2.4, p23 to:
</p>
<blockquote>
<b>Effects</b>: If &amp;x == this, does nothing; otherwise, merges the
argument list into the list.
</blockquote>
<p><i>[Copenhagen: The proposed resolution does not fix all of the
problems in 23.2.2.4 <a href="lib-containers.html#lib.list.ops"> [lib.list.ops]</a>, p22-25. Three different
paragraphs (23, 24, 25) describe the effects of <tt>merge</tt>.
Changing p23, without changing the other two, appears to introduce
contradictions. Additionally, &quot;merges the argument list into the
list&quot; is excessively vague.]</i></p>
<hr>
<a name="304"><h3>304.&nbsp;Must <tt>*a</tt> return an lvalue when <tt>a</tt> is an input iterator?</h3></a><p>
<b>Section:</b>&nbsp;24.1 <a href="lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Dave Abrahams&nbsp; <b>Date:</b>&nbsp;5 Feb 2001</p>
<p>
We all &quot;know&quot; that input iterators are allowed to produce
values when dereferenced of which there is no other in-memory copy.
</p>
<p>
But: Table 72, with a careful reading, seems to imply that this can only be
the case if the value_type has no members (e.g. is a built-in type).
</p>
<p>The problem occurs in the following entry:</p>
<pre>
a-&gt;m pre: (*a).m is well-defined
Equivalent to (*a).m
</pre>
<p>
<tt>*a.m</tt> can be well-defined if <tt>*a</tt> is not a reference
type, but since <tt>operator-&gt;()</tt> must return a pointer for
<tt>a-&gt;m</tt> to be well-formed, it needs something to return a
pointer <i>to</i>. This seems to indicate that <tt>*a</tt> must be
buffered somewhere to make a legal input iterator.
</p>
<p>I don't think this was intentional.</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Copenhagen: the two obvious possibilities are to keep the
<tt>operator-&gt;</tt> requirement for Input Iterators, and put
in a non-normative note describing how it can be implemented with
proxies, or else moving the <tt>operator-&gt;</tt> requirement
from Input Iterator to Forward Iterator. If we do the former
we'll also have to change <tt>istreambuf_iterator</tt>, because
it has no <tt>operator-&gt;</tt>. A straw poll showed roughly equal
support for the two options.]</i></p>
<hr>
<a name="305"><h3>305.&nbsp;Default behavior of codecvt&lt;wchar_t, char, mbstate_t&gt;::length()</h3></a><p>
<b>Section:</b>&nbsp;22.2.1.5.2 <a href="lib-locales.html#lib.locale.codecvt.virtuals"> [lib.locale.codecvt.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;24 Jan 2001</p>
<p>22.2.1.5/3 introduces codecvt in part with:</p>
<blockquote>
codecvt&lt;wchar_t,char,mbstate_t&gt; converts between the native
character sets for tiny and wide characters. Instantiations on
mbstate_t perform conversion between encodings known to the library
implementor.
</blockquote>
<p>But 22.2.1.5.2/10 describes do_length in part with:</p>
<blockquote>
... codecvt&lt;wchar_t, char, mbstate_t&gt; ... return(s) the lesser of max and
(from_end-from).
</blockquote>
<p>
The semantics of do_in and do_length are linked. What one does must
be consistent with what the other does. 22.2.1.5/3 leads me to
believe that the vendor is allowed to choose the algorithm that
codecvt&lt;wchar_t,char,mbstate_t&gt;::do_in performs so that it makes
his customers happy on a given platform. But 22.2.1.5.2/10 explicitly
says what codecvt&lt;wchar_t,char,mbstate_t&gt;::do_length must
return. And thus indirectly specifies the algorithm that
codecvt&lt;wchar_t,char,mbstate_t&gt;::do_in must perform. I believe
that this is not what was intended and is a defect.
</p>
<p>Discussion from the -lib reflector:
<br>This proposal would have the effect of making the semantics of
all of the virtual functions in <tt>codecvt&lt;wchar_t, char,
mbstate_t&gt;</tt> implementation specified. Is that what we want, or
do we want to mandate specific behavior for the base class virtuals
and leave the implementation specified behavior for the codecvt_byname
derived class? The tradeoff is that former allows implementors to
write a base class that actually does something useful, while the
latter gives users a way to get known and specified---albeit
useless---behavior, and is consistent with the way the standard
handles other facets. It is not clear what the original intention
was.</p>
<p>
Nathan has suggest a compromise: a character that is a widened version
of the characters in the basic execution character set must be
converted to a one-byte sequence, but there is no such requirement
for characters that are not part of the basic execution character set.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 22.2.1.5.2/5 from:
</p>
<p>
The instantiations required in Table 51 (lib.locale.category), namely
codecvt&lt;wchar_t,char,mbstate_t&gt; and
codecvt&lt;char,char,mbstate_t&gt;, store no characters. Stores no more
than (to_limit-to) destination elements. It always leaves the to_next
pointer pointing one beyond the last element successfully stored.
</p>
<p>
to:
</p>
<p>
Stores no more than (to_limit-to) destination elements, and leaves the
to_next pointer pointing one beyond the last element successfully
stored. codecvt&lt;char,char,mbstate_t&gt; stores no characters.
</p>
<p>Change 22.2.1.5.2/10 from:</p>
<blockquote>
-10- Returns: (from_next-from) where from_next is the largest value in
the range [from,from_end] such that the sequence of values in the
range [from,from_next) represents max or fewer valid complete
characters of type internT. The instantiations required in Table 51
(21.1.1.1.1), namely codecvt&lt;wchar_t, char, mbstate_t&gt; and
codecvt&lt;char, char, mbstate_t&gt;, return the lesser of max and
(from_end-from).
</blockquote>
<p>to:</p>
<blockquote>
-10- Returns: (from_next-from) where from_next is the largest value in
the range [from,from_end] such that the sequence of values in the range
[from,from_next) represents max or fewer valid complete characters of
type internT. The instantiation codecvt&lt;char, char, mbstate_t&gt; returns
the lesser of max and (from_end-from).
</blockquote>
<p><i>[Redmond: Nathan suggested an alternative resolution: same as
above, but require that, in the default encoding, a character from the
basic execution character set would map to a single external
character. The straw poll was 8-1 in favor of the proposed
resolution.]</i></p>
<p><b>Rationale:</b></p>
<p>The default encoding should be whatever users of a given platform
would expect to be the most natural. This varies from platform to
platform. In many cases there is a preexisting C library, and users
would expect the default encoding to be whatever C uses in the default
&quot;C&quot; locale. We could impose a guarantee like the one Nathan suggested
(a character from the basic execution character set must map to a
single external character), but this would rule out important
encodings that are in common use: it would rule out Shift-JIS, for
example, and it would rule out a fixed-width encoding of UCS-4.</p>
<hr>
<a name="309"><h3>309.&nbsp;Does sentry catch exceptions?</h3></a><p>
<b>Section:</b>&nbsp;27.6 <a href="lib-iostreams.html#lib.iostream.format"> [lib.iostream.format]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;19 Mar 2001</p>
<p>
The descriptions of the constructors of basic_istream&lt;&gt;::sentry
(27.6.1.1.2 <a href="lib-iostreams.html#lib.istream::sentry"> [lib.istream::sentry]</a>) and basic_ostream&lt;&gt;::sentry
(27.6.2.3 <a href="lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>) do not explain what the functions do in
case an exception is thrown while they execute. Some current
implementations allow all exceptions to propagate, others catch them
and set ios_base::badbit instead, still others catch some but let
others propagate.
</p>
<p>
The text also mentions that the functions may call setstate(failbit)
(without actually saying on what object, but presumably the stream
argument is meant). That may have been fine for
basic_istream&lt;&gt;::sentry prior to issue <a href="lwg-defects.html#195">195</a>, since
the function performs an input operation which may fail. However,
issue <a href="lwg-defects.html#195">195</a> amends 27.6.1.1.2 <a href="lib-iostreams.html#lib.istream::sentry"> [lib.istream::sentry]</a>, p2 to
clarify that the function should actually call setstate(failbit |
eofbit), so the sentence in p3 is redundant or even somewhat
contradictory.
</p>
<p>
The same sentence that appears in 27.6.2.3 <a href="lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>, p3
doesn't seem to be very meaningful for basic_istream&lt;&gt;::sentry
which performs no input. It is actually rather misleading since it
would appear to guide library implementers to calling
setstate(failbit) when os.tie()-&gt;flush(), the only called function,
throws an exception (typically, it's badbit that's set in response to
such an event).
</p>
<p><b>Proposed resolution:</b></p>
<p>Add the following paragraph immediately after
27.6.1.1.2 <a href="lib-iostreams.html#lib.istream::sentry"> [lib.istream::sentry]</a>, p5</p>
<blockquote>
<p>
If an exception is thrown during the preparation then ios::badbit
is turned on* in is's error state.
</p>
<p>
[Footnote: This is done without causing an ios::failure to be thrown.
--- end footnote]
</p>
<p>
If (is.exceptions() &amp; ios_base::badbit)!= 0 then the exception is
rethrown.
</p>
</blockquote>
<p>And strike the following sentence from 27.6.1.1.2 <a href="lib-iostreams.html#lib.istream::sentry"> [lib.istream::sentry]</a>, p5</p>
<blockquote>
During preparation, the constructor may call setstate(failbit)
(which may throw ios_base::failure (lib.iostate.flags))
</blockquote>
<p>Add the following paragraph immediately after
27.6.2.3 <a href="lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>, p3</p>
<blockquote>
<p>
If an exception is thrown during the preparation then ios::badbit
is turned on* in os's error state.
</p>
<p>
[Footnote: This is done without causing an ios::failure to be
thrown. --- end footnote]
</p>
<p>
If (os.exceptions() &amp; ios_base::badbit)!= 0 then the exception
is rethrown.
</p>
</blockquote>
<p>And strike the following sentence from 27.6.2.3 <a href="lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>, p3</p>
<blockquote>
During preparation, the constructor may call setstate(failbit)
(which may throw ios_base::failure (lib.iostate.flags))
</blockquote>
<p>(Note that the removal of the two sentences means that the ctors
will not be able to report the failure of any implementation-dependent
operations referred to in footnotes 280 and 293, unless such
operations throw an exception.)</p>
<p><i>[
Copenhagen: It was agreed that there was an issue here, but there was
disagreement about the resolution. Some LWG members argued that a
sentry's constructor should not catch exceptions, because sentries
should only be used within (un)formatted input functions and that
exception handling is the responsibility of those functions, not of
the sentries.
]</i></p>
<hr>
<a name="310"><h3>310.&nbsp;Is errno a macro?</h3></a><p>
<b>Section:</b>&nbsp;17.4.1.2 <a href="lib-intro.html#lib.headers"> [lib.headers]</a>, 19.3 <a href="lib-diagnostics.html#lib.errno"> [lib.errno]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Steve Clamage&nbsp; <b>Date:</b>&nbsp;21 Mar 2001</p>
<p>
Exactly how should errno be declared in a conforming C++ header?
</p>
<p>
The C standard says in 7.1.4 that it is unspecified whether errno is a
macro or an identifier with external linkage. In some implementations
it can be either, depending on compile-time options. (E.g., on
Solaris in multi-threading mode, errno is a macro that expands to a
function call, but is an extern int otherwise. &quot;Unspecified&quot; allows
such variability.)
</p>
<p>The C++ standard:</p>
<ul>
<li>17.4.1.2 says in a note that errno must be macro in C. (false)</li>
<li>17.4.3.1.3 footnote 166 says errno is reserved as an external
name (true), and implies that it is an identifier.</li>
<li>19.3 simply lists errno as a macro (by what reasoning?) and goes
on to say that the contents of of C++ &lt;errno.h&gt; are the
same as in C, begging the question.</li>
<li>C.2, table 95 lists errno as a macro, without comment.</li>
</ul>
<p>I find no other references to errno.</p>
<p>We should either explicitly say that errno must be a macro, even
though it need not be a macro in C, or else explicitly leave it
unspecified. We also need to say something about namespace std.
A user who includes &lt;cerrno&gt; needs to know whether to write
<tt>errno</tt>, or <tt>::errno</tt>, or <tt>std::errno</tt>, or
else &lt;cerrno&gt; is useless.</p>
<p>Two acceptable fixes:</p>
<ul>
<li><p>errno must be a macro. This is trivially satisfied by adding<br>
&nbsp;&nbsp;#define errno (::std::errno)<br>
to the headers if errno is not already a macro. You then always
write errno without any scope qualification, and it always expands
to a correct reference. Since it is always a macro, you know to
avoid using errno as a local identifer.</p></li>
<li><p>errno is in the global namespace. This fix is inferior, because
::errno is not guaranteed to be well-formed.</p></li>
</ul>
<p><i>[
This issue was first raised in 1999, but it slipped through
the cracks.
]</i></p>
<p><b>Proposed resolution:</b></p>
<p>Change the Note in section 17.4.1.2p5 from</p>
<blockquote>
Note: the names defined as macros in C include the following:
assert, errno, offsetof, setjmp, va_arg, va_end, and va_start.
</blockquote>
<p>to</p>
<blockquote>
Note: the names defined as macros in C include the following:
assert, offsetof, setjmp, va_arg, va_end, and va_start.
</blockquote>
<p>In section 19.3, change paragraph 2 from</p>
<blockquote>
The contents are the same as the Standard C library header
&lt;errno.h&gt;.
</blockquote>
<p>to</p>
<blockquote>
The contents are the same as the Standard C library header
&lt;errno.h&gt;, except that errno shall be defined as a macro.
</blockquote>
<p><b>Rationale:</b></p>
<p>C++ must not leave it up to the implementation to decide whether
or not a name is a macro; it must explicitly specify exactly which
names are required to be macros.</p>
<hr>
<a name="311"><h3>311.&nbsp;Incorrect wording in basic_ostream class synopsis</h3></a><p>
<b>Section:</b>&nbsp;27.6.2.1 <a href="lib-iostreams.html#lib.ostream"> [lib.ostream]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Sawyer&nbsp; <b>Date:</b>&nbsp;21 Mar 2001</p>
<p>In 27.6.2.1 <a href="lib-iostreams.html#lib.ostream"> [lib.ostream]</a>, the synopsis of class basic_ostream says:</p>
<pre>
// partial specializationss
template&lt;class traits&gt;
basic_ostream&lt;char,traits&gt;&amp; operator&lt;&lt;( basic_ostream&lt;char,traits&gt;&amp;,
const char * );
</pre>
<p>Problems:</p>
<ul>
<li>Too many 's's at the end of &quot;specializationss&quot; </li>
<li>This is an overload, not a partial specialization</li>
</ul>
<p><b>Proposed resolution:</b></p>
<p>In the synopsis in 27.6.2.1 <a href="lib-iostreams.html#lib.ostream"> [lib.ostream]</a>, remove the
<i>// partial specializationss</i> comment. Also remove the same
comment (correctly spelled, but still incorrect) from the synopsis in
27.6.2.5.4 <a href="lib-iostreams.html#lib.ostream.inserters.character"> [lib.ostream.inserters.character]</a>.
</p>
<p><i>[
Pre-Redmond: added 27.6.2.5.4 <a href="lib-iostreams.html#lib.ostream.inserters.character"> [lib.ostream.inserters.character]</a> because of Martin's
comment in c++std-lib-8939.
]</i></p>
<hr>
<a name="315"><h3>315.&nbsp;Bad &quot;range&quot; in list::unique complexity</h3></a><p>
<b>Section:</b>&nbsp;23.2.2.4 <a href="lib-containers.html#lib.list.ops"> [lib.list.ops]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Sawyer&nbsp; <b>Date:</b>&nbsp;1 May 2001</p>
<p>
23.2.2.4 <a href="lib-containers.html#lib.list.ops"> [lib.list.ops]</a>, Para 21 describes the complexity of
list::unique as: &quot;If the range (last - first) is not empty, exactly
(last - first) -1 applications of the corresponding predicate,
otherwise no applications of the predicate)&quot;.
</p>
<p>
&quot;(last - first)&quot; is not a range.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the &quot;range&quot; from (last - first) to [first, last).
</p>
<hr>
<a name="316"><h3>316.&nbsp;Vague text in Table 69</h3></a><p>
<b>Section:</b>&nbsp;23.1.2 <a href="lib-containers.html#lib.associative.reqmts"> [lib.associative.reqmts]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;4 May 2001</p>
<p>Table 69 says this about a_uniq.insert(t):</p>
<blockquote>
inserts t if and only if there is no element in the container with key
equivalent to the key of t. The bool component of the returned pair
indicates whether the insertion takes place and the iterator component of the
pair points to the element with key equivalent to the key of t.
</blockquote>
<p>The description should be more specific about exactly how the bool component
indicates whether the insertion takes place.</p>
<p><b>Proposed resolution:</b></p>
<p>Change the text in question to</p>
<blockquote>
...The bool component of the returned pair is true if and only if the insertion
takes place...
</blockquote>
<hr>
<a name="317"><h3>317.&nbsp;Instantiation vs. specialization of facets</h3></a><p>
<b>Section:</b>&nbsp;22 <a href="lib-locales.html#lib.localization"> [lib.localization]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;4 May 2001</p>
<p>
The localization section of the standard refers to specializations of
the facet templates as instantiations even though the required facets
are typically specialized rather than explicitly (or implicitly)
instantiated. In the case of ctype&lt;char&gt; and
ctype_byname&lt;char&gt; (and the wchar_t versions), these facets are
actually required to be specialized. The terminology should be
corrected to make it clear that the standard doesn't mandate explicit
instantiation (the term specialization encompasses both explicit
instantiations and specializations).
</p>
<p><b>Proposed resolution:</b></p>
<p>
In the following paragraphs, replace all occurrences of the word
instantiation or instantiations with specialization or specializations,
respectively:
</p>
<blockquote>
22.1.1.1.1, p4, Table 52, 22.2.1.1, p2, 22.2.1.5, p3, 22.2.1.5.1, p5,
22.2.1.5.2, p10, 22.2.2, p2, 22.2.3.1, p1, 22.2.3.1.2, p1, p2 and p3,
22.2.4.1, p1, 22.2.4.1.2, p1, 22,2,5, p1, 22,2,6, p2, 22.2.6.3.2, p7, and
Footnote 242.
</blockquote>
<p>And change the text in 22.1.1.1.1, p4 from</p>
<blockquote>
An implementation is required to provide those instantiations
for facet templates identified as members of a category, and
for those shown in Table 52:
</blockquote>
<p>to</p>
<blockquote>
An implementation is required to provide those specializations...
</blockquote>
<p><i>[Nathan will review these changes, and will look for places where
explicit specialization is necessary.]</i></p>
<p><b>Rationale:</b></p>
<p>This is a simple matter of outdated language. The language to
describe templates was clarified during the standardization process,
but the wording in clause 22 was never updated to reflect that
change.</p>
<hr>
<a name="318"><h3>318.&nbsp;Misleading comment in definition of numpunct_byname</h3></a><p>
<b>Section:</b>&nbsp;22.2.3.2 <a href="lib-locales.html#lib.locale.numpunct.byname"> [lib.locale.numpunct.byname]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;12 May 2001</p>
<p>The definition of the numpunct_byname template contains the following
comment:</p>
<pre>
namespace std {
template &lt;class charT&gt;
class numpunct_byname : public numpunct&lt;charT&gt; {
// this class is specialized for char and wchar_t.
...
</pre>
<p>There is no documentation of the specializations and it seems
conceivable that an implementation will not explicitly specialize the
template at all, but simply provide the primary template.</p>
<p><b>Proposed resolution:</b></p>
<p>Remove the comment from the text in 22.2.3.2 and from the proposed
resolution of library issue <a href="lwg-defects.html#228">228</a>.</p>
<hr>
<a name="319"><h3>319.&nbsp;Storage allocation wording confuses &quot;Required behavior&quot;, &quot;Requires&quot;</h3></a><p>
<b>Section:</b>&nbsp;18.4.1.1 <a href="lib-support.html#lib.new.delete.single"> [lib.new.delete.single]</a>, 18.4.1.2 <a href="lib-support.html#lib.new.delete.array"> [lib.new.delete.array]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Beman Dawes&nbsp; <b>Date:</b>&nbsp;15 May 2001</p>
<p>The standard specifies 17.3.1.3 <a href="lib-intro.html#lib.structure.specifications"> [lib.structure.specifications]</a> that &quot;Required
behavior&quot; elements describe &quot;the semantics of a function definition
provided by either the implementation or a C++ program.&quot;</p>
<p>The standard specifies 17.3.1.3 <a href="lib-intro.html#lib.structure.specifications"> [lib.structure.specifications]</a> that &quot;Requires&quot;
elements describe &quot;the preconditions for calling the function.&quot;</p>
<p>In the sections noted below, the current wording specifies
&quot;Required Behavior&quot; for what are actually preconditions, and thus
should be specified as &quot;Requires&quot;.</p>
<p><b>Proposed resolution:</b></p>
<p>In 18.4.1.1 <a href="lib-support.html#lib.new.delete.single"> [lib.new.delete.single]</a> Para 12 Change:</p>
<blockquote>
<p>Required behavior: accept a value of ptr that is null or that was
returned by an earlier call ...</p>
</blockquote>
<p>to:</p>
<blockquote>
<p>Requires: the value of ptr is null or the value returned by an
earlier call ...</p>
</blockquote>
<p>In 18.4.1.2 <a href="lib-support.html#lib.new.delete.array"> [lib.new.delete.array]</a> Para 11 Change:</p>
<blockquote>
<p>Required behavior: accept a value of ptr that is null or that was
returned by an earlier call ...</p>
</blockquote>
<p>to:</p>
<blockquote>
<p>Requires: the value of ptr is null or the value returned by an
earlier call ...</p>
</blockquote>
<hr>
<a name="320"><h3>320.&nbsp;list::assign overspecified</h3></a><p>
<b>Section:</b>&nbsp;23.2.2.1 <a href="lib-containers.html#lib.list.cons"> [lib.list.cons]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;17 May 2001</p>
<p>
Section 23.2.2.1, paragraphs 6-8 specify that list assign (both forms) have
the &quot;effects&quot; of a call to erase followed by a call to insert.
</p>
<p>
I would like to document that implementers have the freedom to implement
assign by other methods, as long as the end result is the same and the
exception guarantee is as good or better than the basic guarantee.
</p>
<p>
The motivation for this is to use T's assignment operator to recycle
existing nodes in the list instead of erasing them and reallocating
them with new values. It is also worth noting that, with careful
coding, most common cases of assign (everything but assignment with
true input iterators) can elevate the exception safety to strong if
T's assignment has a nothrow guarantee (with no extra memory cost).
Metrowerks does this. However I do not propose that this subtlety be
standardized. It is a QoI issue. </p>
<p>Existing practise:
Metrowerks and SGI recycle nodes, Dinkumware and Rogue Wave don't.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change 23.2.2.1/7 from:</p>
<blockquote>
<p>Effects:</p>
<pre>
erase(begin(), end());
insert(begin(), first, last);
</pre>
</blockquote>
<p>to:</p>
<blockquote>
<p>Effects: Replaces the contents of the list with the range [first, last).</p>
</blockquote>
<p>In 23.1.1 <a href="lib-containers.html#lib.sequence.reqmts"> [lib.sequence.reqmts]</a>, in Table 67 (sequence requirements),
add a new row:</p>
<pre>
a.assign(i,j) void pre: i,j are not iterators into a.
Replaces elements in a with copies
of elements in [i, j).
</pre>
<p>Change 23.2.2.1/8 from:</p>
<blockquote>
<p>Effects:</p>
<pre>
erase(begin(), end());
insert(begin(), n, t);
</pre>
</blockquote>
<p>to:</p>
<blockquote>
<p>Effects: Replaces the contents of the list with n copies of t.</p>
</blockquote>
<p><i>[Redmond: Proposed resolution was changed slightly. Previous
version made explicit statement about exception safety, which wasn't
consistent with the way exception safety is expressed elsewhere.
Also, the change in the sequence requirements is new. Without that
change, the proposed resolution would have required that assignment of
a subrange would have to work. That too would have been
overspecification; it would effectively mandate that assignment use a
temporary.
]</i></p>
<hr>
<a name="321"><h3>321.&nbsp;Typo in num_get</h3></a><p>
<b>Section:</b>&nbsp;22.2.2.1.2 <a href="lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Kevin Djang&nbsp; <b>Date:</b>&nbsp;17 May 2001</p>
<p>
Section 22.2.2.1.2 at p7 states that &quot;A length specifier is added to
the conversion function, if needed, as indicated in Table 56.&quot;
However, Table 56 uses the term &quot;length modifier&quot;, not &quot;length
specifier&quot;.
</p>
<p><b>Proposed resolution:</b></p>
<p>
In 22.2.2.1.2 at p7, change the text &quot;A length specifier is added ...&quot;
to be &quot;A length modifier is added ...&quot;
</p>
<p><b>Rationale:</b></p>
<p>C uses the term &quot;length modifier&quot;. We should be consistent.</p>
<hr>
<a name="322"><h3>322.&nbsp;iterator and const_iterator should have the same value type</h3></a><p>
<b>Section:</b>&nbsp;23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;17 May 2001</p>
<p>
It's widely assumed that, if X is a container,
iterator_traits&lt;X::iterator&gt;::value_type and
iterator_traits&lt;X::const_iterator&gt;::value_type should both be
X::value_type. However, this is nowhere stated. The language in
Table 65 is not precise about the iterators' value types (it predates
iterator_traits), and could even be interpreted as saying that
iterator_traits&lt;X::const_iterator&gt;::value_type should be &quot;const
X::value_type&quot;.
</p>
<p>Related issue: <a href="lwg-closed.html#279">279</a>.</p>
<p><b>Proposed resolution:</b></p>
<p>In Table 65 (&quot;Container Requirements&quot;), change the return type for
X::iterator to &quot;iterator type whose value type is T&quot;. Change the
return type for X::const_iterator to &quot;constant iterator type whose
value type is T&quot;.</p>
<p><b>Rationale:</b></p>
<p>
This belongs as a container requirement, rather than an iterator
requirement, because the whole notion of iterator/const_iterator
pairs is specific to containers' iterator.
</p>
<p>
It is existing practice that (for example)
iterator_traits&lt;list&lt;int&gt;::const_iterator&gt;::value_type
is &quot;int&quot;, rather than &quot;const int&quot;. This is consistent with
the way that const pointers are handled: the standard already
requires that iterator_traits&lt;const int*&gt;::value_type is int.
</p>
<hr>
<a name="323"><h3>323.&nbsp;abs() overloads in different headers</h3></a><p>
<b>Section:</b>&nbsp;26.5 <a href="lib-numerics.html#lib.c.math"> [lib.c.math]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Dave Abrahams&nbsp; <b>Date:</b>&nbsp;4 June 2001</p>
<p>Currently the standard mandates the following overloads of
abs():</p>
<pre>
abs(long), abs(int) in &lt;cstdlib&gt;
abs(float), abs(double), abs(long double) in &lt;cmath&gt;
template&lt;class T&gt; T abs(const complex&lt;T&gt;&amp;) in &lt;complex&gt;
template&lt;class T&gt; valarray&lt;T&gt; abs(const valarray&lt;T&gt;&amp;); in &lt;valarray&gt;
</pre>
<p>
The problem is that having only some overloads visible of a function
that works on &quot;implicitly inter-convertible&quot; types is dangerous in
practice. The headers that get included at any point in a translation
unit can change unpredictably during program
development/maintenance. The wrong overload might be unintentionally
selected.
</p>
<p>
Currently, there is nothing that mandates the simultaneous visibility
of these overloads. Indeed, some vendors have begun fastidiously
reducing dependencies among their (public) headers as a QOI issue: it
helps people to write portable code by refusing to compile unless all
the correct headers are #included.
</p>
<p>The same issue may exist for other functions in the library.</p>
<p>Redmond: PJP reports that C99 adds two new kinds of abs: comples,
and int_max_abs.</p>
<p>Related issue: <a href="lwg-closed.html#343">343</a>.</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Redmond: General agreement that the current situation is
somewhat fragile. No consensus on whether it's more fragile than any
number of other things, or whether there's any good way to fix it.
Walter suggests that <tt>abs</tt> should be defined for all built-in
types in both &lt;cmath&gt; and &lt;cstdlib&gt;, but that no effort
should be made to put all overloads for class types in one place.
Beman suggests closing this issue as &quot;NAD Future&quot;, and adding a
&lt;all&gt; header as an extension. The &lt;all&gt; header would
solve a more general problem: users who can't remember which names are
defined in which headers. (See issue <a href="lwg-closed.html#343">343</a>)]</i></p>
<hr>
<a name="324"><h3>324.&nbsp;Do output iterators have value types?</h3></a><p>
<b>Section:</b>&nbsp;24.1.2 <a href="lib-iterators.html#lib.output.iterators"> [lib.output.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Dave Abrahams&nbsp; <b>Date:</b>&nbsp;7 June 2001</p>
<p>Table 73 suggests that output iterators have value types. It
requires the expression &quot;*a = t&quot;. Additionally, although Table 73
never lists &quot;a = t&quot; or &quot;X(a) = t&quot; in the &quot;expressions&quot; column, it
contains a note saying that &quot;a = t&quot; and &quot;X(a) = t&quot; have equivalent
(but nowhere specified!) semantics.</p>
<p>According to 24.1/9, t is supposed to be &quot;a value of value type
T&quot;:</p>
<blockquote>
In the following sections, a and b denote values of X, n denotes a
value of the difference type Distance, u, tmp, and m denote
identifiers, r denotes a value of X&amp;, t denotes a value of
value type T.
</blockquote>
<p>Two other parts of the standard that are relevant to whether
output iterators have value types:</p>
<ul>
<li>24.1/1 says &quot;All iterators i support the expression *i,
resulting in a value of some class, enumeration, or built-in type
T, called the value type of the iterator&quot;.</li>
<li>
24.3.1/1, which says &quot;In the case of an output iterator, the types
iterator_traits&lt;Iterator&gt;::difference_type
iterator_traits&lt;Iterator&gt;::value_type are both defined as void.&quot;
</li>
</ul>
<p>The first of these passages suggests that &quot;*i&quot; is supposed to
return a useful value, which contradicts the note in 24.1.2/2 saying
that the only valid use of &quot;*i&quot; for output iterators is in an
expression of the form &quot;*i = t&quot;. The second of these passages appears
to contradict Table 73, because it suggests that &quot;*i&quot;'s return value
should be void. The second passage is also broken in the case of a an
iterator type, like non-const pointers, that satisfies both the output
iterator requirements and the forward iterator requirements.</p>
<p>What should the standard say about <tt>*i</tt>'s return value when
i is an output iterator, and what should it say about that t is in the
expression &quot;*i = t&quot;? Finally, should the standard say anything about
output iterators' pointer and reference types?</p>
<p><b>Proposed resolution:</b></p>
<p>24.1 p1, change</p>
<blockquote>
<p>All iterators <tt>i</tt> support the expression <tt>*i</tt>, resulting
in a value of some class, enumeration, or built-in type <tt>T</tt>,
called the value type of the itereator.</p>
</blockquote>
<p>to</p>
<blockquote>
<p>All input iterators <tt>i</tt> support the expression <tt>*i</tt>,
resulting in a value of some class, enumeration, or built-in type
<tt>T</tt>, called the value type of the iterator. All output
iterators support the expression <tt>*i = o</tt> where <tt>o</tt> is a
value of some type that is in the set of types that are <i>writable</i> to
the particular iterator type of <tt>i</tt>.
</p>
</blockquote>
<p>24.1 p9, add</p>
<blockquote>
<p>
<tt>o</tt> denotes a value of some type that is writable to the
output iterator.
</p>
</blockquote>
<p>Table 73, change</p>
<blockquote>
<pre>
*a = t
</pre>
</blockquote>
<p>to</p>
<blockquote>
<pre>
*r = o
</pre>
</blockquote>
<p>and change</p>
<blockquote>
<pre>
*r++ = t
</pre>
</blockquote>
<p>to</p>
<blockquote>
<pre>
*r++ = o
</pre>
</blockquote>
<p><i>[post-Redmond: Jeremy provided wording]</i></p>
<p><b>Rationale:</b></p>
<p>The LWG considered two options: change all of the language that
seems to imply that output iterators have value types, thus making it
clear that output iterators have no value types, or else define value
types for output iterator consistently. The LWG chose the former
option, because it seems clear that output iterators were never
intended to have value types. This was a deliberate design decision,
and any language suggesting otherwise is simply a mistake.</p>
<p>A future revision of the standard may wish to revisit this design
decision.</p>
<hr>
<a name="325"><h3>325.&nbsp;Misleading text in moneypunct&lt;&gt;::do_grouping</h3></a><p>
<b>Section:</b>&nbsp;22.2.6.3.2 <a href="lib-locales.html#lib.locale.moneypunct.virtuals"> [lib.locale.moneypunct.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;02 Jul 2001</p>
<p>The Returns clause in 22.2.6.3.2, p3 says about
moneypunct&lt;charT&gt;::do_grouping()
</p>
<blockquote>
Returns: A pattern defined identically as the result of
numpunct&lt;charT&gt;::do_grouping().241)
</blockquote>
<p>Footnote 241 then reads</p>
<blockquote>
This is most commonly the value &quot;\003&quot; (not &quot;3&quot;).
</blockquote>
<p>
The returns clause seems to imply that the two member functions must
return an identical value which in reality may or may not be true,
since the facets are usually implemented in terms of struct std::lconv
and return the value of the grouping and mon_grouping, respectively.
The footnote also implies that the member function of the moneypunct
facet (rather than the overridden virtual functions in moneypunct_byname)
most commonly return &quot;\003&quot;, which contradicts the C standard which
specifies the value of &quot;&quot; for the (most common) C locale.
</p>
<p><b>Proposed resolution:</b></p>
<p>Replace the text in Returns clause in 22.2.6.3.2, p3 with the following:</p>
<blockquote>
Returns: A pattern defined identically as, but not necessarily
equal to, the result of numpunct&lt;charT&gt;::do_grouping().241)
</blockquote>
<p>and replace the text in Footnote 241 with the following:</p>
<blockquote>
To specify grouping by 3s the value is &quot;\003&quot;, not &quot;3&quot;.
</blockquote>
<p><b>Rationale:</b></p>
<p>
The fundamental problem is that the description of the locale facet
virtuals serves two purposes: describing the behavior of the base
class, and describing the meaning of and constraints on the behavior
in arbitrary derived classes. The new wording makes that separation a
little bit clearer. The footnote (which is nonnormative) is not
supposed to say what the grouping is in the &quot;C&quot; locale or in any other
locale. It is just a reminder that the values are interpreted as small
integers, not ASCII characters.
</p>
<hr>
<a name="327"><h3>327.&nbsp;Typo in time_get facet in table 52</h3></a><p>
<b>Section:</b>&nbsp;22.1.1.1.1 <a href="lib-locales.html#lib.locale.category"> [lib.locale.category]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Tiki Wan&nbsp; <b>Date:</b>&nbsp;06 Jul 2001</p>
<p>The <tt>wchar_t</tt> versions of <tt>time_get</tt> and
<tt>time_get_byname</tt> are listed incorrectly in table 52,
required instantiations. In both cases the second template
parameter is given as OutputIterator. It should instead be
InputIterator, since these are input facets.</p>
<p><b>Proposed resolution:</b></p>
<p>
In table 52, required instantiations, in
22.1.1.1.1 <a href="lib-locales.html#lib.locale.category"> [lib.locale.category]</a>, change</p>
<pre>
time_get&lt;wchar_t, OutputIterator&gt;
time_get_byname&lt;wchar_t, OutputIterator&gt;
</pre>
<p>to</p>
<pre>
time_get&lt;wchar_t, InputIterator&gt;
time_get_byname&lt;wchar_t, InputIterator&gt;
</pre>
<p><i>[Redmond: Very minor change in proposed resolution. Original had
a typo, wchart instead of wchar_t.]</i></p>
<hr>
<a name="328"><h3>328.&nbsp;Bad sprintf format modifier in money_put&lt;&gt;::do_put()</h3></a><p>
<b>Section:</b>&nbsp;22.2.6.2.2 <a href="lib-locales.html#lib.locale.money.put.virtuals"> [lib.locale.money.put.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;07 Jul 2001</p>
<p>The sprintf format string , &quot;%.01f&quot; (that's the digit one), in the
description of the do_put() member functions of the money_put facet in
22.2.6.2.2, p1 is incorrect. First, the f format specifier is wrong
for values of type long double, and second, the precision of 01
doesn't seem to make sense. What was most likely intended was
&quot;%.0Lf&quot;., that is a precision of zero followed by the L length
modifier.</p>
<p><b>Proposed resolution:</b></p>
<p>Change the format string to &quot;%.0Lf&quot;.</p>
<p><b>Rationale:</b></p>
<p>Fixes an obvious typo</p>
<hr>
<a name="329"><h3>329.&nbsp;vector capacity, reserve and reallocation</h3></a><p>
<b>Section:</b>&nbsp;23.2.4.2 <a href="lib-containers.html#lib.vector.capacity"> [lib.vector.capacity]</a>, 23.2.4.3 <a href="lib-containers.html#lib.vector.modifiers"> [lib.vector.modifiers]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Anthony Williams&nbsp; <b>Date:</b>&nbsp;13 Jul 2001</p>
<p>
There is an apparent contradiction about which circumstances can cause
a reallocation of a vector in Section 23.2.4.2 <a href="lib-containers.html#lib.vector.capacity"> [lib.vector.capacity]</a> and
section 23.2.4.3 <a href="lib-containers.html#lib.vector.modifiers"> [lib.vector.modifiers]</a>.
</p>
<p>23.2.4.2p5 says:</p>
<blockquote>
Notes: Reallocation invalidates all the references, pointers, and iterators
referring to the elements in the sequence. It is guaranteed that no
reallocation takes place during insertions that happen after a call to
reserve() until the time when an insertion would make the size of the vector
greater than the size specified in the most recent call to reserve().
</blockquote>
<p>Which implies if I do</p>
<pre>
std::vector&lt;int&gt; vec;
vec.reserve(23);
vec.reserve(0);
vec.insert(vec.end(),1);
</pre>
<p>then the implementation may reallocate the vector for the insert,
as the size specified in the previous call to reserve was zero.</p>
<p>However, the previous paragraphs (23.2.4.2, p1-2) state:</p>
<blockquote>
<p>
(capacity) Returns: The total number of elements the vector
can hold without requiring reallocation
</p>
<p>
...After reserve(), capacity() is greater or equal to the
argument of reserve if reallocation happens; and equal to the previous value
of capacity() otherwise...
</p>
</blockquote>
<p>
This implies that vec.capacity() is still 23, and so the insert()
should not require a reallocation, as vec.size() is 0. This is backed
up by 23.2.4.3p1:
</p>
<blockquote>
(insert) Notes: Causes reallocation if the new size is greater than the old
capacity.
</blockquote>
<p>
Though this doesn't rule out reallocation if the new size is less
than the old capacity, I think the intent is clear.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change the wording of 23.2.4.2 <a href="lib-containers.html#lib.vector.capacity"> [lib.vector.capacity]</a> paragraph 5 to:</p>
<blockquote>
Notes: Reallocation invalidates all the references, pointers, and
iterators referring to the elements in the sequence. It is guaranteed
that no reallocation takes place during insertions that happen after a
call to reserve() until the time when an insertion would make the size
of the vector greater than the value of capacity().
</blockquote>
<p><i>[Redmond: original proposed resolution was modified slightly. In
the original, the guarantee was that there would be no reallocation
until the size would be greater than the value of capacity() after the
most recent call to reserve(). The LWG did not believe that the
&quot;after the most recent call to reserve()&quot; added any useful
information.]</i></p>
<p><b>Rationale:</b></p>
<p>There was general agreement that, when reserve() is called twice in
succession and the argument to the second invocation is smaller than
the argument to the first, the intent was for the second invocation to
have no effect. Wording implying that such cases have an effect on
reallocation guarantees was inadvertant.</p>
<hr>
<a name="331"><h3>331.&nbsp;bad declaration of destructor for ios_base::failure</h3></a><p>
<b>Section:</b>&nbsp;27.4.2.1.1 <a href="lib-iostreams.html#lib.ios::failure"> [lib.ios::failure]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;PremAnand M. Rao&nbsp; <b>Date:</b>&nbsp;23 Aug 2001</p>
<p>
With the change in 17.4.4.8 <a href="lib-intro.html#lib.res.on.exception.handling"> [lib.res.on.exception.handling]</a> to state
&quot;An implementation may strengthen the exception-specification for a
non-virtual function by removing listed exceptions.&quot;
(issue <a href="lwg-defects.html#119">119</a>)
and the following declaration of ~failure() in ios_base::failure
</p>
<pre>
namespace std {
class ios_base::failure : public exception {
public:
...
virtual ~failure();
...
};
}
</pre>
<p>the class failure cannot be implemented since in 18.6.1 <a href="lib-support.html#lib.exception"> [lib.exception]</a> the destructor of class exception has an empty
exception specification:</p>
<pre>
namespace std {
class exception {
public:
...
virtual ~exception() throw();
...
};
}
</pre>
<p><b>Proposed resolution:</b></p>
<p>Remove the declaration of ~failure().</p>
<p><b>Rationale:</b></p>
<p>The proposed resolution is consistent with the way that destructors
of other classes derived from <tt>exception</tt> are handled.</p>
<hr>
<a name="333"><h3>333.&nbsp;does endl imply synchronization with the device?</h3></a><p>
<b>Section:</b>&nbsp;27.6.2.7 <a href="lib-iostreams.html#lib.ostream.manip"> [lib.ostream.manip]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;PremAnand M. Rao&nbsp; <b>Date:</b>&nbsp;27 Aug 2001</p>
<p>A footnote in 27.6.2.7 <a href="lib-iostreams.html#lib.ostream.manip"> [lib.ostream.manip]</a> states:</p>
<blockquote>
[Footnote: The effect of executing cout &lt;&lt; endl is to insert a
newline character in the output sequence controlled by cout, then
synchronize it with any external file with which it might be
associated. --- end foonote]
</blockquote>
<p>
Does the term &quot;file&quot; here refer to the external device?
This leads to some implementation ambiguity on systems with fully
buffered files where a newline does not cause a flush to the device.
</p>
<p>
Choosing to sync with the device leads to significant performance
penalties for each call to endl, while not sync-ing leads to
errors under special circumstances.
</p>
<p>
I could not find any other statement that explicitly defined
the behavior one way or the other.
</p>
<p><b>Proposed resolution:</b></p>
<p>Remove footnote 300 from section 27.6.2.7 <a href="lib-iostreams.html#lib.ostream.manip"> [lib.ostream.manip]</a>.</p>
<p><b>Rationale:</b></p>
<p>We already have normative text saying what <tt>endl</tt> does: it
inserts a newline character and calls <tt>flush</tt>. This footnote
is at best redundant, at worst (as this issue says) misleading,
because it appears to make promises about what <tt>flush</tt>
does.</p>
<hr>
<a name="334"><h3>334.&nbsp;map::operator[] specification forces inefficient implementation</h3></a><p>
<b>Section:</b>&nbsp;23.3.1.2 <a href="lib-containers.html#lib.map.access"> [lib.map.access]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Andrea Griffini&nbsp; <b>Date:</b>&nbsp;02 Sep 2001</p>
<p>
The current standard describes map::operator[] using a
code example. That code example is however quite
inefficient because it requires several useless copies
of both the passed key_type value and of default
constructed mapped_type instances.
My opinion is that was not meant by the comitee to
require all those temporary copies.
</p>
<p>Currently map::operator[] behaviour is specified as: </p>
<pre>
Returns:
(*((insert(make_pair(x, T()))).first)).second.
</pre>
<p>
This specification however uses make_pair that is a
template function of which parameters in this case
will be deduced being of type const key_type&amp; and
const T&amp;. This will create a pair&lt;key_type,T&gt; that
isn't the correct type expected by map::insert so
another copy will be required using the template
conversion constructor available in pair to build
the required pair&lt;const key_type,T&gt; instance.
</p>
<p>If we consider calling of key_type copy constructor
and mapped_type default constructor and copy
constructor as observable behaviour (as I think we
should) then the standard is in this place requiring
two copies of a key_type element plus a default
construction and two copy construction of a mapped_type
(supposing the addressed element is already present
in the map; otherwise at least another copy
construction for each type).
</p>
<p>A simple (half) solution would be replacing the description with:</p>
<pre>
Returns:
(*((insert(value_type(x, T()))).first)).second.
</pre>
<p>This will remove the wrong typed pair construction that
requires one extra copy of both key and value.</p>
<p>However still the using of map::insert requires temporary
objects while the operation, from a logical point of view,
doesn't require any. </p>
<p>I think that a better solution would be leaving free an
implementer to use a different approach than map::insert
that, because of its interface, forces default constructed
temporaries and copies in this case.
The best solution in my opinion would be just requiring
map::operator[] to return a reference to the mapped_type
part of the contained element creating a default element
with the specified key if no such an element is already
present in the container. Also a logarithmic complexity
requirement should be specified for the operation.
</p>
<p>
This would allow library implementers to write alternative
implementations not using map::insert and reaching optimal
performance in both cases of the addressed element being
present or absent from the map (no temporaries at all and
just the creation of a new pair inside the container if
the element isn't present).
Some implementer has already taken this option but I think
that the current wording of the standard rules that as
non-conforming.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Replace 23.3.1.2 <a href="lib-containers.html#lib.map.access"> [lib.map.access]</a> paragraph 1 with
</p>
<blockquote>
<p>
-1- Effects: If there is no key equivalent to x in the map, inserts
value_type(x, T()) into the map.
</p>
<p>
-2- Returns: A reference to the mapped_type corresponding to x in *this.
</p>
<p>
-3- Complexity: logarithmic.
</p>
</blockquote>
<p><i>[This is the second option mentioned above. Howard provided
wording. We may also wish to have a blanket statement somewhere in
clause 17 saying that we do not intend the semantics of sample code
fragments to be interpreted as specifing exactly how many copies are
made. See issue <a href="lwg-active.html#98">98</a> for a similar problem.]</i></p>
<hr>
<a name="335"><h3>335.&nbsp;minor issue with char_traits, table 37</h3></a><p>
<b>Section:</b>&nbsp;21.1.1 <a href="lib-strings.html#lib.char.traits.require"> [lib.char.traits.require]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Sawyer&nbsp; <b>Date:</b>&nbsp;06 Sep 2001</p>
<p>
Table 37, in 21.1.1 <a href="lib-strings.html#lib.char.traits.require"> [lib.char.traits.require]</a>, descibes char_traits::assign
as:
</p>
<pre>
X::assign(c,d) assigns c = d.
</pre>
<p>And para 1 says:</p>
<blockquote>
[...] c and d denote values of type CharT [...]
</blockquote>
<p>
Naturally, if c and d are <i>values</i>, then the assignment is
(effectively) meaningless. It's clearly intended that (in the case of
assign, at least), 'c' is intended to be a reference type.
</p>
<p>I did a quick survey of the four implementations I happened to have
lying around, and sure enough they all have signatures:</p>
<pre>
assign( charT&amp;, const charT&amp; );
</pre>
<p>(or the equivalent). It's also described this way in Nico's book.
(Not to mention the synopses of char_traits&lt;char&gt; in 21.1.3.1
and char_traits&lt;wchar_t&gt; in 21.1.3.2...)
</p>
<p><b>Proposed resolution:</b></p>
<p>Add the following to 21.1.1 para 1:</p>
<blockquote>
r denotes an lvalue of CharT
</blockquote>
<p>and change the description of assign in the table to:</p>
<pre>
X::assign(r,d) assigns r = d
</pre>
<hr>
<a name="336"><h3>336.&nbsp;Clause 17 lack of references to deprecated headers</h3></a><p>
<b>Section:</b>&nbsp;17 <a href="lib-intro.html#lib.library"> [lib.library]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Detlef Vollmann&nbsp; <b>Date:</b>&nbsp;05 Sep 2001</p>
<p>From c++std-edit-873:</p>
<p>17.4.1.2 <a href="lib-intro.html#lib.headers"> [lib.headers]</a>, Table 11. In this table, the header
&lt;strstream&gt; is missing.</p>
<p>This shows a general problem: The whole clause 17 refers quite
often to clauses 18 through 27, but D.7 is also a part of the standard
library (though a deprecated one).</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Redmond: The LWG agrees that &lt;strstream&gt; should be added
to table 11. A review is needed to determine whether there are any
other places in clause 17 where clause D material should be referred
to. Beman will review clause 17.]</i></p>
<hr>
<a name="337"><h3>337.&nbsp;replace_copy_if's template parameter should be InputIterator</h3></a><p>
<b>Section:</b>&nbsp;25.2.4 <a href="lib-algorithms.html#lib.alg.replace"> [lib.alg.replace]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Detlef Vollmann&nbsp; <b>Date:</b>&nbsp;07 Sep 2001</p>
<p>From c++std-edit-876:</p>
<p>
In section 25.2.4 <a href="lib-algorithms.html#lib.alg.replace"> [lib.alg.replace]</a> before p4: The name of the first
parameter of template replace_copy_if should be &quot;InputIterator&quot;
instead of &quot;Iterator&quot;. According to 17.3.2.1 <a href="lib-intro.html#lib.type.descriptions"> [lib.type.descriptions]</a> p1 the
parameter name conveys real normative meaning.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change <tt>Iterator</tt> to <tt>InputIterator</tt>.</p>
<hr>
<a name="338"><h3>338.&nbsp; is whitespace allowed between `-' and a digit?</h3></a><p>
<b>Section:</b>&nbsp;22.2 <a href="lib-locales.html#lib.locale.categories"> [lib.locale.categories]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;17 Sep 2001</p>
<p>
From Stage 2 processing in 22.2.2.1.2 <a href="lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>, p8 and 9 (the
original text or the text corrected by the proposed resolution of
issue <a href="lwg-defects.html#221">221</a>) it seems clear that no whitespace is allowed
within a number, but 22.2.3.1 <a href="lib-locales.html#lib.locale.numpunct"> [lib.locale.numpunct]</a>, p2, which gives the
format for integer and floating point values, says that whitespace is
optional between a plusminus and a sign.
</p>
<p>
The text needs to be clarified to either consistently allow or
disallow whitespace between a plusminus and a sign. It might be
worthwhile to consider the fact that the C library stdio facility does
not permit whitespace embedded in numbers and neither does the C or
C++ core language (the syntax of integer-literals is given in 2.13.1 <a href="lex.html#lex.icon"> [lex.icon]</a>, that of floating-point-literals in 2.13.3 <a href="lex.html#lex.fcon"> [lex.fcon]</a> of the C++ standard).
</p>
<p><b>Proposed resolution:</b></p>
<p>Change the first part of 22.2.3.1 <a href="lib-locales.html#lib.locale.numpunct"> [lib.locale.numpunct]</a> paragraph 2 from:</p>
<blockquote>
<p>
The syntax for number formats is as follows, where <tt>digit</tt>
represents the radix set specified by the <tt>fmtflags</tt> argument
value, <tt>whitespace</tt> is as determined by the facet
<tt>ctype&lt;charT&gt;</tt> (22.2.1.1), and <tt>thousands-sep</tt> and
<tt>decimal-point</tt> are the results of corresponding
<tt>numpunct&lt;charT&gt;</tt> members. Integer values have the
format:
</p>
<pre>
integer ::= [sign] units
sign ::= plusminus [whitespace]
plusminus ::= '+' | '-'
units ::= digits [thousands-sep units]
digits ::= digit [digits]
</pre>
</blockquote>
<p>to:</p>
<blockquote>
<p>
The syntax for number formats is as follows, where <tt>digit</tt>
represents the radix set specified by the <tt>fmtflags</tt> argument
value, and <tt>thousands-sep</tt> and <tt>decimal-point</tt> are the
results of corresponding <tt>numpunct&lt;charT&gt;</tt> members.
Integer values have the format:
</p>
<pre>
integer ::= [sign] units
sign ::= plusminus
plusminus ::= '+' | '-'
units ::= digits [thousands-sep units]
digits ::= digit [digits]
</pre>
</blockquote>
<p><b>Rationale:</b></p>
<p>It's not clear whether the format described in 22.2.3.1 <a href="lib-locales.html#lib.locale.numpunct"> [lib.locale.numpunct]</a> paragraph 2 has any normative weight: nothing in the
standard says how, or whether, it's used. However, there's no reason
for it to differ gratuitously from the very specific description of
numeric processing in 22.2.2.1.2 <a href="lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>. The proposed
resolution removes all mention of &quot;whitespace&quot; from that format.</p>
<hr>
<a name="339"><h3>339.&nbsp;definition of bitmask type restricted to clause 27</h3></a><p>
<b>Section:</b>&nbsp;22.2.1 <a href="lib-locales.html#lib.category.ctype"> [lib.category.ctype]</a>, 17.3.2.1.2 <a href="lib-intro.html#lib.bitmask.types"> [lib.bitmask.types]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;17 September 2001</p>
<p>
The ctype_category::mask type is declared to be an enum in 22.2.1 <a href="lib-locales.html#lib.category.ctype"> [lib.category.ctype]</a> with p1 then stating that it is a bitmask type, most
likely referring to the definition of bitmask type in 17.3.2.1.2 <a href="lib-intro.html#lib.bitmask.types"> [lib.bitmask.types]</a>, p1. However, the said definition only applies to
clause 27, making the reference in 22.2.1 somewhat dubious.
</p>
<p><b>Proposed resolution:</b></p>
<p>Clarify 17.3.2.1.2, p1 by changing the current text from</p>
<blockquote>
Several types defined in clause 27 are bitmask types. Each bitmask type
can be implemented as an enumerated type that overloads certain operators,
as an integer type, or as a bitset (23.3.5 <a href="lib-containers.html#lib.template.bitset"> [lib.template.bitset]</a>).
</blockquote>
<p>to read</p>
<blockquote>
Several types defined in clauses lib.language.support through
lib.input.output and Annex D are bitmask types. Each bitmask type can
be implemented as an enumerated type that overloads certain operators,
as an integer type, or as a bitset (lib.template.bitset).
</blockquote>
<p>
Additionally, change the definition in 22.2.1 to adopt the same
convention as in clause 27 by replacing the existing text with the
following (note, in particluar, the cross-reference to 17.3.2.1.2 in
22.2.1, p1):
</p>
<blockquote>
<p>22.2.1 The ctype category [lib.category.ctype]</p>
<pre>
namespace std {
class ctype_base {
public:
typedef T mask;
// numeric values are for exposition only.
static const mask space = 1 &lt;&lt; 0;
static const mask print = 1 &lt;&lt; 1;
static const mask cntrl = 1 &lt;&lt; 2;
static const mask upper = 1 &lt;&lt; 3;
static const mask lower = 1 &lt;&lt; 4;
static const mask alpha = 1 &lt;&lt; 5;
static const mask digit = 1 &lt;&lt; 6;
static const mask punct = 1 &lt;&lt; 7;
static const mask xdigit = 1 &lt;&lt; 8;
static const mask alnum = alpha | digit;
static const mask graph = alnum | punct;
};
}
</pre>
<p>The type <tt>mask</tt> is a bitmask type (17.3.2.1.2 <a href="lib-intro.html#lib.bitmask.types"> [lib.bitmask.types]</a>).</p>
</blockquote>
<hr>
<a name="340"><h3>340.&nbsp;interpretation of <tt>has_facet&lt;Facet&gt;(loc)</tt>
</h3></a><p>
<b>Section:</b>&nbsp;22.1.1.1.1 <a href="lib-locales.html#lib.locale.category"> [lib.locale.category]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2001</p>
<p>
It's unclear whether 22.1.1.1.1, p3 says that
<tt>has_facet&lt;Facet&gt;(loc)</tt> returns true for any <tt>Facet</tt>
from Table 51 or whether it includes Table 52 as well:
</p>
<blockquote>
For any locale <tt>loc</tt> either constructed, or returned by
locale::classic(), and any facet <tt>Facet</tt> that is a member of a
standard category, <tt>has_facet&lt;Facet&gt;(loc)</tt> is true. Each
locale member function which takes a <tt>locale::category</tt>
argument operates on the corresponding set of facets.
</blockquote>
<p>
It seems that it comes down to which facets are considered to be members of a
standard category. Intuitively, I would classify all the facets in Table 52 as
members of their respective standard categories, but there are an unbounded set
of them...
</p>
<p>
The paragraph implies that, for instance, <tt>has_facet&lt;num_put&lt;C,
OutputIterator&gt; &gt;(loc)</tt> must always return true. I don't think that's
possible. If it were, then <tt>use_facet&lt;num_put&lt;C, OutputIterator&gt;
&gt;(loc)</tt> would have to return a reference to a distinct object for each
valid specialization of <tt>num_put&lt;C, OutputIteratory&gt;</tt>, which is
clearly impossible.
</p>
<p>
On the other hand, if none of the facets in Table 52 is a member of a standard
category then none of the locale member functions that operate on entire
categories of facets will work properly.
</p>
<p>
It seems that what p3 should mention that it's required (permitted?)
to hold only for specializations of <tt>Facet</tt> from Table 52 on
<tt>C</tt> from the set { <tt>char</tt>, <tt>wchar_t</tt> }, and
<tt>InputIterator</tt> and <tt>OutputIterator</tt> from the set of
{
{i,o}<tt>streambuf_iterator</tt>&lt;{<tt>char</tt>,<tt>wchar_t</tt>}<tt>&gt;</tt>
}.
</p>
<p><b>Proposed resolution:</b></p>
<p>In 22.1.1.1.1 <a href="lib-locales.html#lib.locale.category"> [lib.locale.category]</a>, paragraph 3, change
&quot;that is a member of a standard category&quot; to &quot;shown in Table 51&quot;.</p>
<p><b>Rationale:</b></p>
<p>The facets in Table 52 are an unbounded set. Locales should not be
required to contain an infinite number of facets.</p>
<p>It's not necessary to talk about which values of InputIterator and
OutputIterator must be supported. Table 51 already contains a
complete list of the ones we need.</p>
<hr>
<a name="341"><h3>341.&nbsp;Vector reallocation and swap</h3></a><p>
<b>Section:</b>&nbsp;23.2.4.2 <a href="lib-containers.html#lib.vector.capacity"> [lib.vector.capacity]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Anthony Williams&nbsp; <b>Date:</b>&nbsp;27 Sep 2001</p>
<p>It is a common idiom to reduce the capacity of a vector by swapping it with
an empty one:</p>
<pre>
std::vector&lt;SomeType&gt; vec;
// fill vec with data
std::vector&lt;SomeType&gt;().swap(vec);
// vec is now empty, with minimal capacity
</pre>
<p>However, the wording of 23.2.4.2 <a href="lib-containers.html#lib.vector.capacity"> [lib.vector.capacity]</a>paragraph 5 prevents
the capacity of a vector being reduced, following a call to
reserve(). This invalidates the idiom, as swap() is thus prevented
from reducing the capacity. The proposed wording for issue <a href="lwg-active.html#329">329</a> does not affect this. Consequently, the example above
requires the temporary to be expanded to cater for the contents of
vec, and the contents be copied across. This is a linear-time
operation.</p>
<p>However, the container requirements state that swap must have constant
complexity (23.1 <a href="lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a> note to table 65).</p>
<p>This is an important issue, as reallocation affects the validity of
references and iterators.</p>
<p>If the wording of 23.2.4.2p5 is taken to be the desired intent, then
references and iterators remain valid after a call to swap, if they refer to
an element before the new end() of the vector into which they originally
pointed, in which case they refer to the element at the same index position.
Iterators and references that referred to an element whose index position
was beyond the new end of the vector are invalidated.</p>
<p>If the note to table 65 is taken as the desired intent, then there are two
possibilities with regard to iterators and references:</p>
<ol>
<li>All Iterators and references into both vectors are invalidated.</li>
<li>Iterators and references into either vector remain valid, and remain
pointing to the same element. Consequently iterators and references that
referred to one vector now refer to the other, and vice-versa.</li>
</ol>
<p><b>Proposed resolution:</b></p>
<p>Add a new paragraph after 23.2.4.2 <a href="lib-containers.html#lib.vector.capacity"> [lib.vector.capacity]</a> paragraph 5:</p>
<blockquote>
<pre>
void swap(vector&lt;T,Allocator&gt;&amp; x);
</pre>
<p>
<b>Effects:</b> Exchanges the contents and capacity() of <tt>*this</tt>
with that of <tt>x</tt>.</p>
<p>
<b>Complexity:</b> Constant time.</p>
</blockquote>
<p><i>[This solves the problem reported for this issue. We may also
have a problem with a circular definition of swap() for other
containers.]</i></p>
<p><b>Rationale:</b></p>
<p>
swap should be constant time. The clear intent is that it should just
do pointer twiddling, and that it should exchange all properties of
the two vectors, including their reallocation guarantees.
ay be useful.
</p>
<hr>
<a name="342"><h3>342.&nbsp;seek and eofbit</h3></a><p>
<b>Section:</b>&nbsp;27.6.1.3 <a href="lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;09 Oct 201</p>
<p>I think we have a defect.</p>
<p>According to lwg issue <a href="lwg-defects.html#60">60</a> which is now a dr, the
description of seekg in 27.6.1.3 <a href="lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a> paragraph 38 now looks
like:</p>
<blockquote>
Behaves as an unformatted input function (as described in 27.6.1.3,
paragraph 1), except that it does not count the number of characters
extracted and does not affect the value returned by subsequent calls to
gcount(). After constructing a sentry object, if fail() != true,
executes rdbuf()&shy;&gt;pubseekpos( pos).
</blockquote>
<p>And according to lwg issue <a href="lwg-defects.html#243">243</a> which is also now a dr,
27.6.1.3, paragraph 1 looks like:</p>
<blockquote>
Each unformatted input function begins execution by constructing an
object of class sentry with the default argument noskipws (second)
argument true. If the sentry object returns true, when converted to a
value of type bool, the function endeavors to obtain the requested
input. Otherwise, if the sentry constructor exits by throwing an
exception or if the sentry object returns false, when converted to a
value of type bool, the function returns without attempting to obtain
any input. In either case the number of extracted characters is set to
0; unformatted input functions taking a character array of non-zero
size as an argument shall also store a null character (using charT())
in the first location of the array. If an exception is thrown during
input then ios::badbit is turned on in *this'ss error state. If
(exception()&amp;badbit)!= 0 then the exception is rethrown. It also counts
the number of characters extracted. If no exception has been thrown it
ends by storing the count in a member object and returning the value
specified. In any event the sentry object is destroyed before leaving
the unformatted input function.
</blockquote>
<p>And finally 27.6.1.1.2/5 says this about sentry:</p>
<blockquote>
If, after any preparation is completed, is.good() is true, ok_ != false
otherwise, ok_ == false.
</blockquote>
<p>
So although the seekg paragraph says that the operation proceeds if
!fail(), the behavior of unformatted functions says the operation
proceeds only if good(). The two statements are contradictory when only
eofbit is set. I don't think the current text is clear which condition
should be respected.
</p>
<p><b>Further discussion from Redmond:</b></p>
<p>PJP: It doesn't seem quite right to say that <tt>seekg</tt> is
&quot;unformatted&quot;. That makes specific claims about sentry that
aren't quite appropriate for seeking, which has less fragile failure
modes than actual input. If we do really mean that it's unformatted
input, it should behave the same way as other unformatted input. On
the other hand, &quot;principle of least surprise&quot; is that seeking from EOF
ought to be OK.</p>
<p>Dietmar: nothing should depend on eofbit. Eofbit should only be
examined by the user to determine why something failed.</p>
<p><i>[Taken from c++std-lib-8873, c++std-lib-8874, c++std-lib-8876]</i></p>
<p><b>Proposed resolution:</b></p>
<p><i>[Howard will do a survey to find out if there are any other
places where we have a problem, where the difference between
<tt>fail()</tt> and <tt>!good()</tt> is important.]</i></p>
<hr>
<a name="345"><h3>345.&nbsp;type tm in &lt;cwchar&gt;</h3></a><p>
<b>Section:</b>&nbsp;21.4 <a href="lib-strings.html#lib.c.strings"> [lib.c.strings]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Clark Nelson&nbsp; <b>Date:</b>&nbsp;19 Oct 2001</p>
<p>
C99, and presumably amendment 1 to C90, specify that &lt;wchar.h&gt;
declares struct tm as an incomplete type. However, table 48 in 21.4 <a href="lib-strings.html#lib.c.strings"> [lib.c.strings]</a> does not mention the type tm as being declared in
&lt;cwchar&gt;. Is this omission intentional or accidental?
</p>
<p><b>Proposed resolution:</b></p>
<p>In section 21.4 <a href="lib-strings.html#lib.c.strings"> [lib.c.strings]</a>, add &quot;tm&quot; to table 48.</p>
<hr>
<a name="346"><h3>346.&nbsp;Some iterator member functions should be const</h3></a><p>
<b>Section:</b>&nbsp;24.1 <a href="lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Jeremy Siek&nbsp; <b>Date:</b>&nbsp;20 Oct 2001</p>
<p>Iterator member functions and operators that do not change the state
of the iterator should be defined as const member functions or as
functions that take iterators either by const reference or by
value. The standard does not explicitly state which functions should
be const. Since this a fairly common mistake, the following changes
are suggested to make this explicit.</p>
<p>The tables almost indicate constness properly through naming: r
for non-const and a,b for const iterators. The following changes
make this more explicit and also fix a couple problems.</p>
<p><b>Proposed resolution:</b></p>
<p>In 24.1 <a href="lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a> Change the first section of p9 from
&quot;In the following sections, a and b denote values of X...&quot; to
&quot;In the following sections, a and b denote values of type const X...&quot;.</p>
<p>In Table 73, change</p>
<pre>
a-&gt;m U&amp; ...
</pre>
<p>to</p>
<pre>
a-&gt;m const U&amp; ...
r-&gt;m U&amp; ...
</pre>
<p>In Table 73 expression column, change</p>
<pre>
*a = t
</pre>
<p>to</p>
<pre>
*r = t
</pre>
<p><i>[Redmond: The container requirements should be reviewed to see if
the same problem appears there.]</i></p>
<hr>
<a name="347"><h3>347.&nbsp;locale::category and bitmask requirements</h3></a><p>
<b>Section:</b>&nbsp;22.1.1.1.1 <a href="lib-locales.html#lib.locale.category"> [lib.locale.category]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;P.J. Plauger, Nathan Myers&nbsp; <b>Date:</b>&nbsp;23 Oct 2001</p>
<p>
In 22.1.1.1.1 <a href="lib-locales.html#lib.locale.category"> [lib.locale.category]</a> paragraph 1, the category members
are described as bitmask elements. In fact, the bitmask requirements
in 17.3.2.1.2 <a href="lib-intro.html#lib.bitmask.types"> [lib.bitmask.types]</a> don't seem quite right: <tt>none</tt>
and <tt>all</tt> are bitmask constants, not bitmask elements.</p>
<p>In particular, the requirements for <tt>none</tt> interact poorly
with the requirement that the LC_* constants from the C library must
be recognizable as C++ locale category constants. LC_* values should
not be mixed with these values to make category values.</p>
<p>We have two options for the proposed resolution. Informally:
option 1 removes the requirement that LC_* values be recognized as
category arguments. Option 2 changes the category type so that this
requirement is implementable, by allowing <tt>none</tt> to be some
value such as 0x1000 instead of 0.</p>
<p>Nathan writes: &quot;I believe my proposed resolution [Option 2] merely
re-expresses the status quo more clearly, without introducing any
changes beyond resolving the DR.</p>
<p><b>Proposed resolution:</b></p>
<p>
<b>Option 1:</b> <br>
Replace the first two paragraphs of 22.1.1.1 <a href="lib-locales.html#lib.locale.types"> [lib.locale.types]</a> with:</p>
<blockquote>
<pre>
typedef int category;
</pre>
<p>Valid category values include the <tt>locale</tt> member bitmask
elements <tt>collate</tt>, <tt>ctype</tt>, <tt>monetary</tt>,
<tt>numeric</tt>, <tt>time</tt>, and <tt>messages</tt>, each of which
represents a single locale category. In addition, <tt>locale</tt> member
bitmask constant <tt>none</tt> is defined as zero and represents no
category. And locale member bitmask constant <tt>all</tt> is defined such that
the expression</p>
<pre>
(collate | ctype | monetary | numeric | time | messages | all) == all
</pre>
<p>
is <tt>true</tt>, and represents the union of all categories. Further
the expression <tt>(X | Y)</tt>, where <tt>X</tt> and <tt>Y</tt> each
represent a single category, represents the union of the two
categories.
</p>
<p>
<tt>locale</tt> member functions expecting a <tt>category</tt>
argument require one of the <tt>category</tt> values defined above, or
the union of two or more such values. Such a <tt>category</tt>
argument identifies a set of locale categories. Each locale category,
in turn, identifies a set of locale facets, including at least those
shown in Table 51:
</p>
</blockquote>
<p>
<b>Option 2:</b> <br>
Replace the first paragraph of 22.1.1.1 <a href="lib-locales.html#lib.locale.types"> [lib.locale.types]</a> with:</p>
<blockquote>
<p>
Valid category values include the enumerated values. In addition, the
result of applying commutative operators | and &amp; to any two valid
values is valid, and results in the setwise union and intersection,
respectively, of the argument categories. The values <tt>all</tt> and
<tt>none</tt> are defined such that for any valid value <tt>cat</tt>, the
expressions <tt>(cat | all == all)</tt>, <tt>(cat &amp; all == cat)</tt>,
<tt>(cat | none == cat)</tt> and <tt>(cat &amp; none == none)</tt> are
true. For non-equal values <tt>cat1</tt> and <tt>cat2</tt> of the
remaining enumerated values, <tt>(cat1 &amp; cat2 == none)</tt> is true.
For any valid categories <tt>cat1</tt> and <tt>cat2</tt>, the result
of <tt>(cat1 &amp; ~cat2)</tt> is valid, and equals the setwise union of
those categories found in <tt>cat1</tt> but not found in <tt>cat2</tt>.
[Footnote: it is not required that <tt>all</tt> equal the setwise union
of the other enumerated values; implementations may add extra categories.]
</p>
</blockquote>
<hr>
<a name="348"><h3>348.&nbsp;Minor issue with std::pair operator&lt;</h3></a><p>
<b>Section:</b>&nbsp;20.2.2 <a href="lib-utilities.html#lib.pairs"> [lib.pairs]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Sawyer&nbsp; <b>Date:</b>&nbsp;23 Oct 2001</p>
<p>
The current wording of 20.2.2 [lib.pairs] p6 precludes the use of
operator&lt; on any pair type which contains a pointer.
</p>
<p><b>Proposed resolution:</b></p>
<p>In 20.2.2 <a href="lib-utilities.html#lib.pairs"> [lib.pairs]</a> paragraph 6, replace:</p>
<pre>
Returns: x.first &lt; y.first || (!(y.first &lt; x.first) &amp;&amp; x.second &lt;
y.second).
</pre>
<p>With:</p>
<pre>
Returns: std::less&lt;T1&gt;()( x.first, y.first ) ||
(!std::less&lt;T1&gt;()( y.first, x.first) &amp;&amp;
std::less&lt;T2&gt;()( x.second, y.second ) )
</pre>
<hr>
<a name="349"><h3>349.&nbsp;Minor typographical error in ostream_iterator</h3></a><p>
<b>Section:</b>&nbsp;24.5.2 <a href="lib-iterators.html#lib.ostream.iterator"> [lib.ostream.iterator]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Sawyer&nbsp; <b>Date:</b>&nbsp;24 Oct 2001</p>
<p>24.5.2 [lib.ostream.iterator] states:</p>
<pre>
[...]
private:
// basic_ostream&lt;charT,traits&gt;* out_stream; exposition only
// const char* delim; exposition only
</pre>
<p>Whilst it's clearly marked &quot;exposition only&quot;, I suspect 'delim'
should be of type 'const charT*'.</p>
<p><b>Proposed resolution:</b></p>
<p>
In 24.5.2 <a href="lib-iterators.html#lib.ostream.iterator"> [lib.ostream.iterator]</a>, replace <tt>const char* delim</tt> with
<tt>const charT* delim</tt>.
</p>
<hr>
<a name="350"><h3>350.&nbsp;allocator&lt;&gt;::address</h3></a><p>
<b>Section:</b>&nbsp;20.4.1.1 <a href="lib-utilities.html#lib.allocator.members"> [lib.allocator.members]</a>, 20.1.5 <a href="lib-utilities.html#lib.allocator.requirements"> [lib.allocator.requirements]</a>, 17.4.1.1 <a href="lib-intro.html#lib.contents"> [lib.contents]</a>&nbsp; <b>Status:</b>&nbsp;<a href="lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Nathan Myers&nbsp; <b>Date:</b>&nbsp;25 Oct 2001</p>
<p>See c++std-lib-9006 and c++std-lib-9007. This issue is taken
verbatim from -9007.</p>
<p>
The core language feature allowing definition of operator&amp;() applied
to any non-builtin type makes that operator often unsafe to use in
implementing libraries, including the Standard Library. The result
is that many library facilities fail for legal user code, such as
the fragment</p>
<pre>
class A { private: A* operator&amp;(); };
std::vector&lt;A&gt; aa;
class B { };
B* operator&amp;(B&amp;) { return 0; }
std::vector&lt;B&gt; ba;
</pre>
<p>
In particular, the requirements table for Allocator (Table 32) specifies
no semantics at all for member address(), and allocator&lt;&gt;::address is
defined in terms of unadorned operator &amp;.
</p>
<p><b>Proposed resolution:</b></p>
<p>
In 20.4.1.1, Change the definition of allocator&lt;&gt;::address from:</p>
<blockquote>
Returns: &amp;x
</blockquote>
<p>to:</p>
<p>
Returns: The value that the built in operator&amp;(x) would return if not
overloaded.
</p>
<p>
In 20.1.5, Table 32, add to the Notes column of the a.address(r) and
a.address(s) lines, respectively:
</p>
<pre>
allocator&lt;T&gt;::address(r)
allocator&lt;T&gt;::address(s)
</pre>
<p>In addition, in clause 17.4.1.1, add a statement:</p>
<blockquote>
The Standard Library does not apply operator&amp; to any type for which
operator&amp; may be overloaded.
</blockquote>
<p><b>Rationale:</b></p>
<p>The obvious implementations for std::allocator&lt;&gt;::address are</p>
<pre>
T* reinterpret_cast&lt;T*&gt;(&amp;static_cast&lt;char&amp;&gt;(o));
</pre>
<p>and</p>
<pre>
T const* reinterpret_cast&lt;T const*&gt;(&amp;static_cast&lt;char const&amp;&gt;(o));
</pre>
<p>
but to define them formally in terms of reinterpret_cast&lt;&gt; seems
to introduce semantic difficulties best avoided. Using a.address()
should not introduce unspecified or implementation-defined semantics
into a user program.</p>
<p>----- End of document -----</p>
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