1<?xml version='1.0'?> 2<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" 3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" 4[ ]> 5 6<chapter id="std.diagnostics" xreflabel="Diagnostics"> 7<?dbhtml filename="diagnostics.html"?> 8 9<chapterinfo> 10 <keywordset> 11 <keyword> 12 ISO C++ 13 </keyword> 14 <keyword> 15 library 16 </keyword> 17 </keywordset> 18</chapterinfo> 19 20<title> 21 Diagnostics 22 <indexterm><primary>Diagnostics</primary></indexterm> 23</title> 24 25<sect1 id="std.diagnostics.exceptions" xreflabel="Exceptions"> 26 <?dbhtml filename="exceptions.html"?> 27 <title>Exceptions</title> 28 29 <sect2 id="std.diagnostics.exceptions.api"> 30 <title>API Reference</title> 31 <para> 32 All exception objects are defined in one of the standard header 33 files: <filename>exception</filename>, 34 <filename>stdexcept</filename>, <filename>new</filename>, and 35 <filename>typeinfo</filename>. 36 </para> 37 38 <para> 39 The base exception object is <classname>exception</classname>, 40 located in <filename>exception</filename>. This object has no 41 <classname>string</classname> member. 42 </para> 43 44 <para> 45 Derived from this are several classes that may have a 46 <classname>string</classname> member: a full hierarchy can be 47 found in the source documentation. 48 </para> 49 50 <para> 51 Full API details. 52 </para> 53 54 <!-- Doxygen XML: api/group__exceptions.xml --> 55 56 </sect2> 57 <sect2 id="std.diagnostics.exceptions.data" xreflabel="Adding Data to Exceptions"> 58 <title>Adding Data to <classname>exception</classname></title> 59 <para> 60 The standard exception classes carry with them a single string as 61 data (usually describing what went wrong or where the 'throw' took 62 place). It's good to remember that you can add your own data to 63 these exceptions when extending the hierarchy: 64 </para> 65 <programlisting> 66 struct My_Exception : public std::runtime_error 67 { 68 public: 69 My_Exception (const string& whatarg) 70 : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { } 71 int errno_at_time_of_throw() const { return e; } 72 DBID id_of_thing_that_threw() const { return id; } 73 protected: 74 int e; 75 DBID id; // some user-defined type 76 }; 77 </programlisting> 78 79 </sect2> 80</sect1> 81 82<sect1 id="std.diagnostics.concept_checking" xreflabel="Concept Checking"> 83 <title>Concept Checking</title> 84 <para> 85 In 1999, SGI added <quote>concept checkers</quote> to their 86 implementation of the STL: code which checked the template 87 parameters of instantiated pieces of the STL, in order to insure 88 that the parameters being used met the requirements of the 89 standard. For example, the Standard requires that types passed as 90 template parameters to <classname>vector</classname> be 91 "Assignable" (which means what you think it means). The 92 checking was done during compilation, and none of the code was 93 executed at runtime. 94 </para> 95 <para> 96 Unfortunately, the size of the compiler files grew significantly 97 as a result. The checking code itself was cumbersome. And bugs 98 were found in it on more than one occasion. 99 </para> 100 <para> 101 The primary author of the checking code, Jeremy Siek, had already 102 started work on a replacement implementation. The new code has been 103 formally reviewed and accepted into 104 <ulink url="http://www.boost.org/libs/concept_check/concept_check.htm">the 105 Boost libraries</ulink>, and we are pleased to incorporate it into the 106 GNU C++ library. 107 </para> 108 <para> 109 The new version imposes a much smaller space overhead on the generated 110 object file. The checks are also cleaner and easier to read and 111 understand. 112 </para> 113 114 <para> 115 They are off by default for all versions of GCC. 116 They can be enabled at configure time with 117 <link linkend="manual.intro.setup.configure"><literal>--enable-concept-checks</literal></link>. 118 You can enable them on a per-translation-unit basis with 119 <literal>-D_GLIBCXX_CONCEPT_CHECKS</literal>. 120 </para> 121 122 <para> 123 Please note that the upcoming C++ standard has first-class 124 support for template parameter constraints based on concepts in the core 125 language. This will obviate the need for the library-simulated concept 126 checking described above. 127 </para> 128 129</sect1> 130 131</chapter> 132