docs/doxygen/overviews/debugging.h

   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 group_funcmacro_log, @ref group_funcmacro_debug
  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 group_funcmacro_debug 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