2000-04-22 04:33:34 +08:00
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="AUTHOR" CONTENT="pme@sourceware.cygnus.com (Phil Edwards)">
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<META NAME="KEYWORDS" CONTENT="HOWTO, libstdc++, egcs, g++, libg++, STL">
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<META NAME="DESCRIPTION" CONTENT="HOWTO for the libstdc++ chapter 19.">
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<META NAME="GENERATOR" CONTENT="vi and eight fingers">
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<TITLE>libstdc++-v3 HOWTO: Chapter 19</TITLE>
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<LINK REL="home" HREF="http://sourceware.cygnus.com/libstdc++/docs/19_diagnostics/">
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<LINK REL=StyleSheet HREF="../lib3styles.css">
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2000-07-08 05:13:28 +08:00
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<!-- $Id: howto.html,v 1.1 2000/04/21 20:33:31 bkoz 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 19: Diagnostics</A></H1>
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<P>Chapter 19 deals with program diagnostics, such as exceptions
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and assertions. You know, all the things we wish weren't even
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necessary at all.
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</P>
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<!-- ####################################################### -->
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<HR>
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<H1>Contents</H1>
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<UL>
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<LI><A HREF="#1">Adding data to exceptions</A>
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<LI><A HREF="#2">Exception class hierarchy diagram</A>
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<LI><A HREF="#3">Concept checkers</A>
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</UL>
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<HR>
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<!-- ####################################################### -->
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<H2><A NAME="1">Adding data to exceptions</A></H2>
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<P>The standard exception classes carry with them a single string as
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data (usually describing what went wrong or where the 'throw' took
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place). It's good to remember that you can add your own data to
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these exceptions when extending the heirarchy:
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</P>
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<PRE>
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using std::runtime_error;
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struct My_Exception : public runtime_error
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{
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public:
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My_Exception (const string& whatarg)
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: runtime_error(whatarg), e(errno), id(GetDataBaseID()) { }
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int errno_at_time_of_throw() const { return e; }
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DBID id_of_thing_that_threw() const { return id; }
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protected:
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int e;
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DBID id; // some user-defined type
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};
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</PRE>
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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="2">Exception class hierarchy diagram</A></H2>
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<P>The <A HREF="exceptions_hiearchy.pdf">diagram</A> is in PDF, or
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at least it will be once it gets finished.
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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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2000-07-08 05:13:28 +08:00
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<HR>
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<H2><A NAME="3">Concept checkers</A></H2>
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<P>As part of their 3.3 release, SGI added some nifty macros which
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perform assertions on type properties. For example, the Standard
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requires that types passed as template parameters to <TT>vector</TT>
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be "Assignable" (which means what you think it means).
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</P>
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<P>The concept checkers allow the source code for <TT>vector</TT> to
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declare
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<PRE>
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__STL_CLASS_REQUIRES(_Tp, _Assignable);
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</PRE>inside the template. <TT>_Tp</TT> is the element type of the
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vector, and <TT>_Assignable</TT> is the concept to be checked (it is
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defined in some back-end header files). When you instantiate
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<TT>vector<MyType></TT>, compile-time checking can be done on
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whether MyType meets the requirements for vectors.
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</P>
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<P>This is an extension to the library. This documentation needs updating.</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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2000-04-22 04:33:34 +08:00
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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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<A HREF="mailto:pme@sourceware.cygnus.com">Phil Edwards</A> or
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<A HREF="mailto:gdr@egcs.cygnus.com">Gabriel Dos Reis</A>.
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<BR> $Id: howto.html,v 1.1 2000/04/21 20:33:31 bkoz Exp $
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</EM></P>
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