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1 /////////////////////////////////////////////////////////////////////////////
2 // Name: debugging.h
3 // Purpose: topic overview
4 // Author: wxWidgets team
5 // RCS-ID: $Id$
6 // Licence: wxWindows license
7 /////////////////////////////////////////////////////////////////////////////
8
9 /**
10
11 @page overview_debugging Debugging
12
13 Classes, functions and macros: wxDebugContext, wxObject, wxLog,
14 @ref page_func_cat_log, @ref page_macro_cat_debugging
15
16 Various classes, functions and macros are provided in wxWidgets to help you debug
17 your application. Most of these are only available if you compile both wxWidgets,
18 your application and @e all libraries that use wxWidgets with the __WXDEBUG__ symbol
19 defined. You can also test the __WXDEBUG__ symbol in your own applications to execute
20 code that should be active only in debug mode.
21
22 @li @ref overview_debugging_dbgctx
23 @li @ref overview_debugging_dbgmacros
24 @li @ref overview_debugging_logging
25 @li @ref overview_debugging_dbgctx2
26
27
28 <hr>
29
30
31 @section overview_debugging_dbgctx wxDebugContext
32
33 wxDebugContext is a class that never gets instantiated, but ties together
34 various static functions and variables. It allows you to dump all objects to that stream,
35 write statistics about object allocation, and check memory for errors.
36
37 It is good practice to define a wxObject::Dump member function for each class you derive
38 from a wxWidgets class, so that wxDebugContext::Dump can call it and
39 give valuable information about the state of the application.
40
41 If you have difficulty tracking down a memory leak, recompile
42 in debugging mode and call wxDebugContext::Dump and wxDebugContext::PrintStatistics at
43 appropriate places. They will tell you what objects have not yet been
44 deleted, and what kinds of object they are. In fact, in debug mode wxWidgets will automatically
45 detect memory leaks when your application is about to exit, and if there are any leaks,
46 will give you information about the problem. (How much information depends on the operating system
47 and compiler -- some systems don't allow all memory logging to be enabled). See the
48 memcheck sample for example of usage.
49
50 For wxDebugContext to do its work, the @e new and @e delete operators for wxObject
51 have been redefined to store extra information about dynamically allocated objects
52 (but not statically declared objects).
53
54 This slows down a debugging version of an application, but can
55 find difficult-to-detect memory leaks (objects are not
56 deallocated), overwrites (writing past the end of your object) and
57 underwrites (writing to memory in front of the object).
58
59 If debugging mode is on and the symbols wxUSE_GLOBAL_MEMORY_OPERATORS and
60 wxUSE_DEBUG_NEW_ALWAYS are set to 1 in setup.h, 'new' is defined to be:
61
62 @code
63 #define new new(__FILE__,__LINE__)
64 @endcode
65
66 All occurrences of 'new' in wxWidgets and your own application will use
67 the overridden form of the operator with two extra arguments. This means that
68 the debugging output (and error messages reporting memory problems) will tell you what
69 file and on what line you allocated the object. Unfortunately not all
70 compilers allow this definition to work properly, but most do.
71
72
73
74 @section overview_debugging_dbgmacros Debug macros
75
76 You should also use @ref page_macro_cat_debugging as part of a 'defensive programming'
77 strategy, scattering wxASSERTs liberally to test for problems in your code as early as
78 possible.
79 Forward thinking will save a surprising amount of time in the long run.
80
81 #wxASSERT is used to pop up an error message box when a condition
82 is not @true. You can also use #wxASSERT_MSG to supply your
83 own helpful error message. For example:
84
85 @code
86 void MyClass::MyFunction(wxObject* object)
87 {
88 wxASSERT_MSG( (object != NULL), "object should not be NULL in MyFunction!" );
89
90 ...
91 };
92 @endcode
93
94 The message box allows you to continue execution or abort the program. If you are running
95 the application inside a debugger, you will be able to see exactly where the problem was.
96
97
98
99 @section overview_debugging_logging Logging functions
100
101 You can use the wxLogDebug and wxLogTrace functions to output debugging information in
102 debug mode; it will do nothing for non-debugging code.
103
104
105
106 @section overview_debugging_dbgctx2 wxDebugContext overview
107
108 Class: wxDebugContext
109
110 wxDebugContext is a class for performing various debugging and memory tracing operations.
111
112 This class has only static data and function members, and there should be
113 no instances. Probably the most useful members are SetFile (for directing output
114 to a file, instead of the default standard error or debugger output);
115 Dump (for dumping the dynamically allocated objects) and PrintStatistics
116 (for dumping information about allocation of objects). You can also call
117 Check to check memory blocks for integrity.
118
119 Here's an example of use. The SetCheckpoint ensures that only the
120 allocations done after the checkpoint will be dumped.
121
122 @code
123 wxDebugContext::SetCheckpoint();
124
125 wxDebugContext::SetFile("c:\\temp\\debug.log");
126
127 wxString *thing = new wxString;
128
129 char *ordinaryNonObject = new char[1000];
130
131 wxDebugContext::Dump();
132 wxDebugContext::PrintStatistics();
133 @endcode
134
135 You can use wxDebugContext if __WXDEBUG__ is defined, or you can use it
136 at any other time (if wxUSE_DEBUG_CONTEXT is set to 1 in setup.h). It is not disabled
137 in non-debug mode because you may not wish to recompile wxWidgets and your entire application
138 just to make use of the error logging facility.
139
140 @note wxDebugContext::SetFile has a problem at present, so use the default stream instead.
141 Eventually the logging will be done through the wxLog facilities instead.
142
143 */
144