1<?xml version="1.0" encoding="ISO-8859-1"?> 2<!DOCTYPE html 3 PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 4 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 5 6<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 7<head> 8 <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> 9 <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" /> 10 <meta name="KEYWORDS" content="HOWTO, libstdc++, GCC, g++, libg++, STL" /> 11 <meta name="DESCRIPTION" content="HOWTO for the libstdc++ chapter 19." /> 12 <meta name="GENERATOR" content="vi and eight fingers" /> 13 <title>libstdc++-v3 HOWTO: Chapter 19: Diagnostics</title> 14<link rel="StyleSheet" href="../lib3styles.css" type="text/css" /> 15<link rel="Start" href="../documentation.html" type="text/html" 16 title="GNU C++ Standard Library" /> 17<link rel="Prev" href="../18_support/howto.html" type="text/html" 18 title="Library Support" /> 19<link rel="Next" href="../20_util/howto.html" type="text/html" 20 title="General Utilities" /> 21<link rel="Copyright" href="../17_intro/license.html" type="text/html" /> 22<link rel="Help" href="../faq/index.html" type="text/html" title="F.A.Q." /> 23</head> 24<body> 25 26<h1 class="centered"><a name="top">Chapter 19: Diagnostics</a></h1> 27 28<p>Chapter 19 deals with program diagnostics, such as exceptions 29 and assertions. You know, all the things we wish weren't even 30 necessary at all. 31</p> 32 33 34<!-- ####################################################### --> 35<hr /> 36<h1>Contents</h1> 37<ul> 38 <li><a href="#1">Adding data to exceptions</a></li> 39 <li><a href="#2">Exception class hierarchy diagram</a></li> 40 <li><a href="#3">Concept checkers -- <strong>new and improved!</strong></a></li> 41</ul> 42 43<hr /> 44 45<!-- ####################################################### --> 46 47<h2><a name="1">Adding data to exceptions</a></h2> 48 <p>The standard exception classes carry with them a single string as 49 data (usually describing what went wrong or where the 'throw' took 50 place). It's good to remember that you can add your own data to 51 these exceptions when extending the hierarchy: 52 </p> 53 <pre> 54 struct My_Exception : public std::runtime_error 55 { 56 public: 57 My_Exception (const string& whatarg) 58 : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { } 59 int errno_at_time_of_throw() const { return e; } 60 DBID id_of_thing_that_threw() const { return id; } 61 protected: 62 int e; 63 DBID id; // some user-defined type 64 }; 65 </pre> 66 <p>Return <a href="#top">to top of page</a> or 67 <a href="../faq/index.html">to the FAQ</a>. 68 </p> 69 70<hr /> 71<h2><a name="2">Exception class hierarchy diagram</a></h2> 72 <p>At one point we were going to make up a PDF of the exceptions 73 hierarchy, akin to the one done for the I/O class hierarchy. 74 Time was our enemy. Since then we've moved to Doxygen, which has 75 the useful property of not sucking. Specifically, when the source 76 code is changed, the diagrams are automatically brought up to date. 77 For the old way, we had to update the diagrams separately. 78 </p> 79 <p>There are several links to the Doxygen-generated pages from 80 <a href="../documentation.html">here</a>. 81 </p> 82 <p>Return <a href="#top">to top of page</a> or 83 <a href="../faq/index.html">to the FAQ</a>. 84 </p> 85 86<hr /> 87<h2><a name="3">Concept checkers -- <strong>new and improved!</strong></a></h2> 88 <p>Better taste! Less fat! Literally!</p> 89 <p>In 1999, SGI added <em>concept checkers</em> to their implementation 90 of the STL: code which checked the template parameters of 91 instantiated pieces of the STL, in order to insure that the parameters 92 being used met the requirements of the standard. For example, 93 the Standard requires that types passed as template parameters to 94 <code>vector</code> be "Assignable" (which means what you think 95 it means). The checking was done during compilation, and none of 96 the code was executed at runtime. 97 </p> 98 <p>Unfortunately, the size of the compiler files grew significantly 99 as a result. The checking code itself was cumbersome. And bugs 100 were found in it on more than one occasion. 101 </p> 102 <p>The primary author of the checking code, Jeremy Siek, had already 103 started work on a replacement implementation. The new code has been 104 formally reviewed and accepted into 105 <a href="http://www.boost.org/libs/concept_check/concept_check.htm">the 106 Boost libraries</a>, and we are pleased to incorporate it into the 107 GNU C++ library. 108 </p> 109 <p>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 </p> 113 <p>They are off by default for all versions of GCC from 3.0 to 3.4 (the 114 latest release at the time of writing). 115 They can be enabled at configure time with 116 <a href="../configopts.html"><code>--enable-concept-checks</code></a>. 117 You can enable them on a per-translation-unit basis with 118 <code>#define _GLIBCXX_CONCEPT_CHECKS</code> for GCC 3.4 and higher 119 (or with <code>#define _GLIBCPP_CONCEPT_CHECKS</code> for versions 120 3.1, 3.2 and 3.3). 121 </p> 122 <p>Return <a href="#top">to top of page</a> or 123 <a href="../faq/index.html">to the FAQ</a>. 124 </p> 125 126<!-- ####################################################### --> 127 128<hr /> 129<p class="fineprint"><em> 130See <a href="../17_intro/license.html">license.html</a> for copying conditions. 131Comments and suggestions are welcome, and may be sent to 132<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>. 133</em></p> 134 135 136</body> 137</html> 138