1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)">
<meta name="KEYWORDS" content="HOWTO, libstdc++, GCC, g++, libg++, STL">
<meta name="DESCRIPTION" content="HOWTO for the libstdc++ chapter 19.">
<meta name="GENERATOR" content="vi and eight fingers">
<title>libstdc++-v3 HOWTO: Chapter 19</title>
<link rel="StyleSheet" href="../lib3styles.css">
</head>
<body>
<h1 class="centered"><a name="top">Chapter 19: Diagnostics</a></h1>
<p>Chapter 19 deals with program diagnostics, such as exceptions
and assertions. You know, all the things we wish weren't even
necessary at all.
</p>
<!-- ####################################################### -->
<hr>
<h1>Contents</h1>
<ul>
<li><a href="#1">Adding data to exceptions</a>
<li><a href="#2">Exception class hierarchy diagram</a>
<li><a href="#3">Concept checkers -- <strong>new and improved!</strong></a>
<li><a href="#4">Verbose <code>terminate</code></a>
</ul>
<hr>
<!-- ####################################################### -->
<h2><a name="1">Adding data to exceptions</a></h2>
<p>The standard exception classes carry with them a single string as
data (usually describing what went wrong or where the 'throw' took
place). It's good to remember that you can add your own data to
these exceptions when extending the hierarchy:
</p>
<pre>
struct My_Exception : public std::runtime_error
{
public:
My_Exception (const string& whatarg)
: std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { }
int errno_at_time_of_throw() const { return e; }
DBID id_of_thing_that_threw() const { return id; }
protected:
int e;
DBID id; // some user-defined type
};
</pre>
<p>Return <a href="#top">to top of page</a> or
<a href="../faq/index.html">to the FAQ</a>.
</p>
<hr>
<h2><a name="2">Exception class hierarchy diagram</a></h2>
<p>At one point we were going to make up a PDF of the exceptions
hierarchy, akin to the one done for the I/O class hierarchy.
Time was our enemy. Since then we've moved to Doxygen, which has
the useful property of not sucking. Specifically, when the source
code is changed, the diagrams are automatically brought up to date.
For the old way, we had to update the diagrams separately.
</p>
<p>There are several links to the Doxygen-generated pages from
<a href="../documentation.html">here</a>.
</p>
<p>Return <a href="#top">to top of page</a> or
<a href="../faq/index.html">to the FAQ</a>.
</p>
<hr>
<h2><a name="3">Concept checkers -- <strong>new and improved!</strong></a></h2>
<p>Better taste! Less fat! Literally!</p>
<p>In 1999, SGI added <em>concept checkers</em> to their implementation
of the STL: code which checked the template parameters of
instantiated pieces of the STL, in order to insure that the parameters
being used met the requirements of the standard. For example,
the Standard requires that types passed as template parameters to
<code>vector</code> be "Assignable" (which means what you think
it means). The checking was done during compilation, and none of
the code was executed at runtime.
</p>
<p>Unfortunately, the size of the compiler files grew significantly
as a result. The checking code itself was cumbersome. And bugs
were found in it on more than one occasion.
</p>
<p>The primary author of the checking code, Jeremy Siek, had already
started work on a replcement implementation. The new code has been
formally reviewed and accepted into
<a href="http://www.boost.org/libs/concept_check/concept_check.htm">the
Boost libraries</a>, and we are pleased to incorporate it into the
GNU C++ library.
</p>
<p>The new version imposes a much smaller space overhead on the generated
object file. The checks are also cleaner and easier to read and
understand.
</p>
<p>For GCC 3.0 and 3.1 they are off by default. They can be enabled at
configure time with
<a href="../configopts.html"><code>--enable-concept-checks</code></a>.
For 3.1 you can instead #define _GLIBCPP_CONCEPT_CHECKS to enable them
on a per-translation-unit basis.
</p>
<p>Return <a href="#top">to top of page</a> or
<a href="../faq/index.html">to the FAQ</a>.
</p>
<hr>
<h2><a name="4">Verbose <code>terminate</code></a></h2>
<p>If you are having difficulty with uncaught exceptions and want a
little bit of help debugging the causes of the core dumps, you can
make use of a GNU extension in GCC 3.1 and later:
<pre>
#include <exception>
int main()
{
std::set_terminate (__gnu_cxx::__verbose_terminate_handler);
...
throw <em>anything</em>;
}</pre>
</p>
<p>The <code> __verbose_terminate_handler </code> function obtains the name
of the current exception, attempts to demangle it, and prints it to
stderr. If the exception is derived from <code> std::exception </code>
then the output from <code>what()</code> will be included.
</p>
<p>Any replacement termination function is required to kill the program
without returning; this one calls abort.
</p>
<p>For example:
<pre>
#include <exception>
#include <stdexcept>
struct BLARGH : std::runtime_error
{
BLARGH (const string& whatarg)
: std::runtime_error(whatarg) { }
};
int main (int argc)
{
std::set_terminate (__gnu_cxx::__verbose_terminate_handler);
if (argc > 5)
throw BLARGH("argc is greater than 5!");
else
throw argc;
}</pre>
</p>
<p>In GCC 3.1 and later, this gives
<pre>
% ./a.out
terminate called after throwing a `int'
Aborted
% ./a.out f f f f f f f f f f f
terminate called after throwing a `BLARGH'
what(): argc is greater than 5!
Aborted
%</pre>
The 'Aborted' line comes from the call to abort(), of course.
</p>
<p>Return <a href="#top">to top of page</a> or
<a href="../faq/index.html">to the FAQ</a>.
</p>
<!-- ####################################################### -->
<hr>
<p class="fineprint"><em>
See <a href="../17_intro/license.html">license.html</a> for copying conditions.
Comments and suggestions are welcome, and may be sent to
<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
</em></p>
</body>
</html>
|
