2000-04-22 04:33:34 +08:00
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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2000-07-12 05:45:08 +08:00
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<META NAME="AUTHOR" CONTENT="pme@sources.redhat.com (Phil Edwards)">
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2000-04-22 04:33:34 +08:00
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<META NAME="KEYWORDS" CONTENT="HOWTO, libstdc++, gcc, g++, libg++, STL">
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<META NAME="DESCRIPTION" CONTENT="HOWTO for libstdc++ chapter 17.">
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<META NAME="GENERATOR" CONTENT="vi and eight fingers">
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<TITLE>libstdc++-v3 HOWTO: Chapter 17</TITLE>
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<LINK REL=StyleSheet HREF="../lib3styles.css">
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2001-05-31 10:45:04 +08:00
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<!-- $Id: howto.html,v 1.4 2001/05/30 21:54:57 pme Exp $ -->
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2000-04-22 04:33:34 +08:00
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</HEAD>
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<BODY>
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<H1 CLASS="centered"><A NAME="top">Chapter 17: Library Introduction</A></H1>
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<P>Chapter 17 is actually a list of definitions and descriptions used
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in the following chapters of the Standard when describing the actual
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library. Here, we use "Introduction" as an introduction
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to the <EM>GNU implementation of</EM> the ISO Standard C++ Library.
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</P>
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<HR>
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<H1>Contents</H1>
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<UL>
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<LI><A HREF="#2">The Standard C++ header files</A>
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<LI><A HREF="#3">Thread-safety</A>
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<LI><A HREF="#4"><TT><foo></TT> vs <TT><foo.h></TT></A>
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2000-04-25 14:39:48 +08:00
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<LI><A HREF="porting-howto.html">Porting-howto</A>
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2000-04-22 04:33:34 +08:00
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</UL>
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<HR>
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<!-- ####################################################### -->
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<H2><A NAME="2">The Standard C++ header files</A></H2>
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<P>The Standard C++ Library specifies 50 header files that must be
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available to all hosted implementations. Actually, the word
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"files" is a misnomer, since the contents of the headers
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don't necessarily have to be in any kind of external file. The
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only rule is that when you <TT>#include</TT> a certain header, the
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contents of that header, as defined by the Standard, become
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available to you, no matter how.
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</P>
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<P>The names of the headers can be easily seen in
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2000-05-04 00:11:03 +08:00
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<A HREF="headers_cc.txt"><TT>testsuite/17_intro/headers.cc</TT></A>,
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2000-04-22 04:33:34 +08:00
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which is a small testbed we use to make certain that the headers
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all compile and run.
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</P>
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<HR>
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<H2><A NAME="3">Thread-safety</A></H2>
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<P>This is a thorny issue that gets brought up on the libstdc++-v3
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and gcc mailing lists on a regular basis (probably by a cron job).
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This entry will mention a very little bit about the general MT
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issues with libstdc++. The latest status and quick notes will be
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2001-05-30 16:30:04 +08:00
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in FAQ 5.6. Some discussion about thread-safe containers will be
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2000-04-22 04:33:34 +08:00
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in section 6.8 (the HOWTOs on containers).
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</P>
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<P>The libstdc++ code (all of it, not just the containers) has been
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designed so that thread-safety will be easily possible. The first
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(!) problem is finding a <EM>fast</EM> method of implementation
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portable to all platforms. A minor problem that pops up every so
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often is different interpretations of what "thread-safe"
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means for a library (not a general program). We currently use the
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2001-05-30 16:30:04 +08:00
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<A HREF="http://www.sgi.com/tech/stl/thread_safety.html">same
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2000-04-22 04:33:34 +08:00
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definition that SGI</A> uses for their STL subset.
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2001-05-31 10:45:04 +08:00
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<EM>Please see the many cautions given in HOWTOs on containers.</EM>
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</P>
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<P>
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Here is another attempt at explaining the dangers of using the
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STL with threading support without understanding some important
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details. The STL implementation is currently configured to use
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the high-speed caching memory allocator. If you absolutely
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think you must change this on a global basis for your platform
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to support multi-threading, then please consult all commentary
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in include/bits/c++config and the HOWTOs on containers. Be
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fully aware that you may change the external or internal ABI of
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libstdc++-v3 when you provide -D__USE_MALLOC on the command line
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or make a change to that configuration file. [Placeholder in
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case other patches don't make it before the 3.0 release: That
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memory allocator can appear buggy in multithreaded C++ programs
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(and has been reported to leak memory), if STL is misconfigured
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for your platform. You may need to provide -D_PTHREADS on the
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command line in this case to ensure the memory allocator for
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containers is really protected by a mutex. Also, be aware that
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you just changed the ABI of libstdc++-v3 when you did that thus
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your entire application and all libraries must be compiled with
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compatible flags. The STL implementation doesn't currently
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protect you from changing the mutex locking implementation to
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one that doesn't really play together with the implementation
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you may have compiled other application code with.]
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</P>
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<P>
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If you don't like caches of objects being retained inside the
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STL, then you might be tempted to define __USE_MALLOC either on
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the command line or by rebuilding c++config.h. Please note,
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once you define __USE_MALLOC, only the malloc allocator is
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visible to application code (i.e. the typically higher-speed
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allocator is not even available in this configuration). There
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is a better way: It is possible to force the malloc-based
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allocator on a per-case-basis for some application code even
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when the above macro symbol is not defined. The author of this
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comment believes that is a better way to tune an application for
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high-speed using this implementation of the STL. Here is one
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possible example displaying the forcing of the malloc-based
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allocator over the typically higher-speed default allocator:
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std::list <void*, std::malloc_alloc> my_malloc_based_list;
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2000-04-22 04:33:34 +08:00
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</P>
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<P>A recent journal article has described "atomic integer
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operations," which would allow us to, well, perform updates
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on integers atomically, and without requiring an explicit mutex
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lock. This appears promising, but the major difficulty is that
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these operations "may not be available on all systems, and
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if they are, may have different interfaces." [quoting from
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mailing list messages]
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</P>
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<P>Here is a small link farm to threads (no pun) in the mail archives
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that discuss the threading problem. Each link is to the first
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relevent message in the thread; from there you can use
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"Thread Next" to move down the thread. This farm is in
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latest-to-oldest order.
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<UL>
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2001-05-31 10:45:04 +08:00
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<LI><A HREF="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00384.html">
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inspired this most recent updating of issues with threading
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and the SGI STL library. It also contains some example
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POSIX-multithreaded STL code.</A>
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<LI> <A HREF="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00136.html">
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an early analysis of why __USE_MALLOC should be disable for
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the 3.0 release of libstdc++.</A>
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2000-04-22 04:33:34 +08:00
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</UL>
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<BR>
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Here are discussions that took place before the current snapshot;
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they are still relevant and instructive.
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<BR>
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<UL>
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<LI>One way of preventing memory leaks by the old default memory
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allocator in multithreaded code is
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configopts.html, [...]: Remove many EGCS references...
* docs/configopts.html, docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/howto.html, docs/18_support/howto.html,
docs/19_diagnostics/howto.html, docs/20_util/howto.html,
docs/21_strings/howto.html, docs/22_locale/howto.html,
docs/23_containers/howto.html, docs/24_iterators/howto.html,
docs/25_algorithms/howto.html, docs/26_numerics/howto.html,
docs/27_io/howto.html, docs/ext/howto.html, docs/faq/index.html:
Remove many EGCS references; use current absolute URLs on
gcc.gnu.org or sources.redhat.com for messages in list archives.
* docs/faq/index.txt: Regenerate.
From-SVN: r36988
2000-10-21 08:51:50 +08:00
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<A HREF="http://gcc.gnu.org/ml/gcc/1999-11n/msg00431.html">discussed here</A>.
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configopts.html, [...]: Sync with wwwdocs.
* docs/configopts.html, docs/documentation.html,
docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/contribute.html, docs/17_intro/howto.html,
docs/18_support/howto.html, docs/19_diagnostics/howto.html,
docs/20_util/howto.html, docs/21_strings/howto.html,
docs/22_locale/howto.html, docs/23_containers/howto.html,
docs/24_iterators/howto.html, docs/25_algorithms/howto.html,
docs/26_numerics/howto.html, docs/27_io/howto.html,
docs/ext/howto.html, docs/faq/index.html, docs/faq/index.txt: Sync
with wwwdocs.
From-SVN: r37981
2000-12-04 07:47:49 +08:00
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<LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q3/msg00167.html">This thread
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2000-04-22 04:33:34 +08:00
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concerns strings</A>.
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configopts.html, [...]: Sync with wwwdocs.
* docs/configopts.html, docs/documentation.html,
docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/contribute.html, docs/17_intro/howto.html,
docs/18_support/howto.html, docs/19_diagnostics/howto.html,
docs/20_util/howto.html, docs/21_strings/howto.html,
docs/22_locale/howto.html, docs/23_containers/howto.html,
docs/24_iterators/howto.html, docs/25_algorithms/howto.html,
docs/26_numerics/howto.html, docs/27_io/howto.html,
docs/ext/howto.html, docs/faq/index.html, docs/faq/index.txt: Sync
with wwwdocs.
From-SVN: r37981
2000-12-04 07:47:49 +08:00
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<LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00339.html">So does this
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2000-04-22 04:33:34 +08:00
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one</A>. This initial message also refers to another
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thread in the GCC mailing list...
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configopts.html, [...]: Remove many EGCS references...
* docs/configopts.html, docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/howto.html, docs/18_support/howto.html,
docs/19_diagnostics/howto.html, docs/20_util/howto.html,
docs/21_strings/howto.html, docs/22_locale/howto.html,
docs/23_containers/howto.html, docs/24_iterators/howto.html,
docs/25_algorithms/howto.html, docs/26_numerics/howto.html,
docs/27_io/howto.html, docs/ext/howto.html, docs/faq/index.html:
Remove many EGCS references; use current absolute URLs on
gcc.gnu.org or sources.redhat.com for messages in list archives.
* docs/faq/index.txt: Regenerate.
From-SVN: r36988
2000-10-21 08:51:50 +08:00
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<LI><A HREF="http://gcc.gnu.org/ml/gcc/1999-06n/msg00680.html">which is here</A>,
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2000-04-22 04:33:34 +08:00
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and goes on for some time. Ironically, the initial message
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in this thread also mentions another threading thread...
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configopts.html, [...]: Remove many EGCS references...
* docs/configopts.html, docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/howto.html, docs/18_support/howto.html,
docs/19_diagnostics/howto.html, docs/20_util/howto.html,
docs/21_strings/howto.html, docs/22_locale/howto.html,
docs/23_containers/howto.html, docs/24_iterators/howto.html,
docs/25_algorithms/howto.html, docs/26_numerics/howto.html,
docs/27_io/howto.html, docs/ext/howto.html, docs/faq/index.html:
Remove many EGCS references; use current absolute URLs on
gcc.gnu.org or sources.redhat.com for messages in list archives.
* docs/faq/index.txt: Regenerate.
From-SVN: r36988
2000-10-21 08:51:50 +08:00
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<LI><A HREF="http://gcc.gnu.org/ml/gcc-bugs/1999-04n/msg00777.html">beginning here</A>,
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2000-04-22 04:33:34 +08:00
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and talking about pthreads. (Note that a much more recent
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message from the first thread in this list notes that
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configopts.html, [...]: Sync with wwwdocs.
* docs/configopts.html, docs/documentation.html,
docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/contribute.html, docs/17_intro/howto.html,
docs/18_support/howto.html, docs/19_diagnostics/howto.html,
docs/20_util/howto.html, docs/21_strings/howto.html,
docs/22_locale/howto.html, docs/23_containers/howto.html,
docs/24_iterators/howto.html, docs/25_algorithms/howto.html,
docs/26_numerics/howto.html, docs/27_io/howto.html,
docs/ext/howto.html, docs/faq/index.html, docs/faq/index.txt: Sync
with wwwdocs.
From-SVN: r37981
2000-12-04 07:47:49 +08:00
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<A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q3/msg00176.html">pthreads
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2000-04-22 04:33:34 +08:00
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should not be used as a starting point</A> for making
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libstdc++ threadsafe.)
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configopts.html, [...]: Sync with wwwdocs.
* docs/configopts.html, docs/documentation.html,
docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/contribute.html, docs/17_intro/howto.html,
docs/18_support/howto.html, docs/19_diagnostics/howto.html,
docs/20_util/howto.html, docs/21_strings/howto.html,
docs/22_locale/howto.html, docs/23_containers/howto.html,
docs/24_iterators/howto.html, docs/25_algorithms/howto.html,
docs/26_numerics/howto.html, docs/27_io/howto.html,
docs/ext/howto.html, docs/faq/index.html, docs/faq/index.txt: Sync
with wwwdocs.
From-SVN: r37981
2000-12-04 07:47:49 +08:00
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<LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00168.html">This
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2000-04-22 04:33:34 +08:00
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message</A>,
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configopts.html, [...]: Sync with wwwdocs.
* docs/configopts.html, docs/documentation.html,
docs/install.html, docs/17_intro/BADNAMES,
docs/17_intro/contribute.html, docs/17_intro/howto.html,
docs/18_support/howto.html, docs/19_diagnostics/howto.html,
docs/20_util/howto.html, docs/21_strings/howto.html,
docs/22_locale/howto.html, docs/23_containers/howto.html,
docs/24_iterators/howto.html, docs/25_algorithms/howto.html,
docs/26_numerics/howto.html, docs/27_io/howto.html,
docs/ext/howto.html, docs/faq/index.html, docs/faq/index.txt: Sync
with wwwdocs.
From-SVN: r37981
2000-12-04 07:47:49 +08:00
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<A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00159.html">this one</A>,
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and <A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00156.html">this one</A>
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2000-04-22 04:33:34 +08:00
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are the tops of related threads (all within the same time
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period) discussing threading and the IO library. Much of it
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is dealing with the C library, but C++ is included as well.
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</UL>
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</P>
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<P>This section will be updated as new and interesting issues come
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to light.
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</P>
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<P>Return <A HREF="#top">to top of page</A> or
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<A HREF="../faq/index.html">to the FAQ</A>.
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</P>
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<HR>
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<H2><A NAME="4"><TT><foo></TT> vs <TT><foo.h></TT></A></H2>
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<P>The new-style headers are fully supported in libstdc++-v3. The compiler
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2001-05-31 05:55:05 +08:00
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itself fully supports namespaces, including <TT>std::</TT>.
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2000-04-22 04:33:34 +08:00
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</P>
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<P>For those of you new to ISO C++98, no, that isn't a typo, the headers
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really have new names. Marshall Cline's C++ FAQ Lite has a good
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explanation in
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<A HREF="http://www.cerfnet.com/~mpcline/On-Line-C++-FAQ/coding-standards.html#[25.4]">item [25.4]</A>.
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</P>
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<P>Return <A HREF="#top">to top of page</A> or
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<A HREF="../faq/index.html">to the FAQ</A>.
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</P>
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<!-- ####################################################### -->
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<HR>
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<P CLASS="fineprint"><EM>
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Comments and suggestions are welcome, and may be sent to
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2001-04-03 08:26:58 +08:00
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<A HREF="mailto:libstdc++@gcc.gnu.org">the mailing list</A>.
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2001-05-31 10:45:04 +08:00
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<BR> $Id: howto.html,v 1.4 2001/05/30 21:54:57 pme Exp $
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2000-04-22 04:33:34 +08:00
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