2 <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
6 <chapter id="std.diagnostics" xreflabel="Diagnostics">
7 <?dbhtml filename="diagnostics.html"?>
22 <indexterm><primary>Diagnostics</primary></indexterm>
25 <sect1 id="std.diagnostics.exceptions" xreflabel="Exceptions">
26 <?dbhtml filename="exceptions.html"?>
27 <title>Exceptions</title>
29 <sect2 id="std.diagnostics.exceptions.api">
30 <title>API Reference</title>
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>.
39 The base exception object is <classname>exception</classname>,
40 located in <filename>exception</filename>. This object has no
41 <classname>string</classname> member.
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.
54 <!-- Doxygen XML: api/group__exceptions.xml -->
57 <sect2 id="std.diagnostics.exceptions.data" xreflabel="Adding Data to Exceptions">
58 <title>Adding Data to <classname>exception</classname></title>
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:
66 struct My_Exception : public std::runtime_error
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; }
75 DBID id; // some user-defined type
82 <sect1 id="std.diagnostics.concept_checking" xreflabel="Concept Checking">
83 <title>Concept Checking</title>
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
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.
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
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
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>.
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.