2 <!DOCTYPE part PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
6 <part id="manual.diagnostics" xreflabel="Diagnostics">
7 <?dbhtml filename="diagnostics.html"?>
22 <indexterm><primary>Diagnostics</primary></indexterm>
25 <chapter id="manual.diagnostics.exceptions" xreflabel="Exceptions">
26 <?dbhtml filename="exceptions.html"?>
27 <title>Exceptions</title>
29 <sect1 id="manual.diagnostics.exceptions.hierarchy" xreflabel="Exception Classes">
30 <title>Exception Classes</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 <ulink url="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00233.html">source documentation</ulink>.
51 <sect1 id="manual.diagnostics.exceptions.data" xreflabel="Adding Data to Exceptions">
52 <title>Adding Data to Exceptions</title>
54 The standard exception classes carry with them a single string as
55 data (usually describing what went wrong or where the 'throw' took
56 place). It's good to remember that you can add your own data to
57 these exceptions when extending the hierarchy:
60 struct My_Exception : public std::runtime_error
63 My_Exception (const string& whatarg)
64 : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { }
65 int errno_at_time_of_throw() const { return e; }
66 DBID id_of_thing_that_threw() const { return id; }
69 DBID id; // some user-defined type
74 <sect1 id="manual.diagnostics.exceptions.cancellation" xreflabel="Cancellation">
75 <title>Cancellation</title>
81 <chapter id="manual.diagnostics.concept_checking" xreflabel="Concept Checking">
82 <title>Concept Checking</title>
84 In 1999, SGI added <quote>concept checkers</quote> to their
85 implementation of the STL: code which checked the template
86 parameters of instantiated pieces of the STL, in order to insure
87 that the parameters being used met the requirements of the
88 standard. For example, the Standard requires that types passed as
89 template parameters to <classname>vector</classname> be
90 "Assignable" (which means what you think it means). The
91 checking was done during compilation, and none of the code was
95 Unfortunately, the size of the compiler files grew significantly
96 as a result. The checking code itself was cumbersome. And bugs
97 were found in it on more than one occasion.
100 The primary author of the checking code, Jeremy Siek, had already
101 started work on a replacement implementation. The new code has been
102 formally reviewed and accepted into
103 <ulink url="http://www.boost.org/libs/concept_check/concept_check.htm">the
104 Boost libraries</ulink>, and we are pleased to incorporate it into the
108 The new version imposes a much smaller space overhead on the generated
109 object file. The checks are also cleaner and easier to read and
114 They are off by default for all versions of GCC.
115 They can be enabled at configure time with
116 <ulink url="../configopts.html"><literal>--enable-concept-checks</literal></ulink>.
117 You can enable them on a per-translation-unit basis with
118 <literal>-D_GLIBCXX_CONCEPT_CHECKS</literal>.
122 Please note that the upcoming C++ standard has first-class
123 support for template parameter constraints based on concepts in the core
124 language. This will obviate the need for the library-simulated concept
125 checking described above.