1<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" 2 xml:id="std.diagnostics" xreflabel="Diagnostics"> 3<?dbhtml filename="diagnostics.html"?> 4 5<info><title> 6 Diagnostics 7 <indexterm><primary>Diagnostics</primary></indexterm> 8</title> 9 <keywordset> 10 <keyword>ISO C++</keyword> 11 <keyword>library</keyword> 12 </keywordset> 13</info> 14 15 16 17<section xml:id="std.diagnostics.exceptions" xreflabel="Exceptions"><info><title>Exceptions</title></info> 18 <?dbhtml filename="exceptions.html"?> 19 20 21 <section xml:id="std.diagnostics.exceptions.api"><info><title>API Reference</title></info> 22 23 <para> 24 All exception objects are defined in one of the standard header 25 files: <filename>exception</filename>, 26 <filename>stdexcept</filename>, <filename>new</filename>, and 27 <filename>typeinfo</filename>. 28 </para> 29 30 <para> 31 The base exception object is <classname>exception</classname>, 32 located in <filename>exception</filename>. This object has no 33 <classname>string</classname> member. 34 </para> 35 36 <para> 37 Derived from this are several classes that may have a 38 <classname>string</classname> member: a full hierarchy can be 39 found in the source documentation. 40 </para> 41 42 <para> 43 Full API details. 44 </para> 45 46 <!-- Doxygen XML: api/group__exceptions.xml --> 47 48 </section> 49 <section xml:id="std.diagnostics.exceptions.data" xreflabel="Adding Data to Exceptions"><info><title>Adding Data to <classname>exception</classname></title></info> 50 51 <para> 52 The standard exception classes carry with them a single string as 53 data (usually describing what went wrong or where the 'throw' took 54 place). It's good to remember that you can add your own data to 55 these exceptions when extending the hierarchy: 56 </para> 57 <programlisting> 58 struct My_Exception : public std::runtime_error 59 { 60 public: 61 My_Exception (const string& whatarg) 62 : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { } 63 int errno_at_time_of_throw() const { return e; } 64 DBID id_of_thing_that_threw() const { return id; } 65 protected: 66 int e; 67 DBID id; // some user-defined type 68 }; 69 </programlisting> 70 71 </section> 72</section> 73 74<section xml:id="std.diagnostics.concept_checking" xreflabel="Concept Checking"><info><title>Concept Checking</title></info> 75 <?dbhtml filename="concept_checking.html"?> 76 77 <para> 78 In 1999, SGI added <quote>concept checkers</quote> to their 79 implementation of the STL: code which checked the template 80 parameters of instantiated pieces of the STL, in order to insure 81 that the parameters being used met the requirements of the 82 standard. For example, the Standard requires that types passed as 83 template parameters to <classname>vector</classname> be 84 "Assignable" (which means what you think it means). The 85 checking was done during compilation, and none of the code was 86 executed at runtime. 87 </para> 88 <para> 89 Unfortunately, the size of the compiler files grew significantly 90 as a result. The checking code itself was cumbersome. And bugs 91 were found in it on more than one occasion. 92 </para> 93 <para> 94 The primary author of the checking code, Jeremy Siek, had already 95 started work on a replacement implementation. The new code was 96 formally reviewed and accepted into 97 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.boost.org/libs/concept_check/concept_check.htm">the 98 Boost libraries</link>, and we are pleased to incorporate it into the 99 GNU C++ library. 100 </para> 101 <para> 102 The new version imposes a much smaller space overhead on the generated 103 object file. The checks are also cleaner and easier to read and 104 understand. 105 </para> 106 107 <para> 108 They are off by default for all versions of GCC. 109 They can be enabled at configure time with 110 <link linkend="manual.intro.setup.configure"><literal>--enable-concept-checks</literal></link>. 111 You can enable them on a per-translation-unit basis with 112 <literal>-D_GLIBCXX_CONCEPT_CHECKS</literal>. 113 </para> 114 115 <para> 116 Please note that the checks are based on the requirements in the original 117 C++ standard, some of which have changed in the new C++11 revision. 118 Additionally, some correct code might be rejected by the concept checks, 119 for example template argument types may need to be complete when used in 120 a template definition, rather than at the point of instantiation. 121 There are no plans to address these shortcomings. 122 </para> 123 124</section> 125 126</chapter> 127