docs/doxygen/overviews/debugging.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        debugging.h
   3 // Purpose:     topic overview
   4 // Author:      Vadim Zeitlin
   5 // Copyright:   (c) 2009 Vadim Zeitlin <vadim@wxwidgets.org>
   6 // Licence:     wxWindows licence
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_debugging Debugging
  12
  13 @tableofcontents
  14
  15 Various classes, functions and macros are provided in wxWidgets to help you
  16 debug your application. Assertion macros allow you to insert various checks in
  17 your application which can be compiled out or disabled in release builds but
  18 are extremely useful while developing. Logging functions are also provided
  19 which are useful for inserting traces into your application code as well as
  20 debugging. Both assertions and debug logging are also used by wxWidgets itself
  21 so you may encounter them even if you don't use either of these features
  22 yourself.
  23
  24 @see wxLog, @ref group_funcmacro_log, @ref group_funcmacro_debug
  25
  26
  27
  28 @section overview_debugging_config Configuring Debug Support
  29
  30 Starting with wxWidgets 2.9.1 debugging features are always available by
  31 default (and not only in a special "debug" build of the library) and you need
  32 to predefine wxDEBUG_LEVEL symbol as 0 when building both the library and your
  33 application to remove them completely from the generated object code. However
  34 the debugging features are disabled by default when the application itself is
  35 built with @c NDEBUG defined (i.e. in "release" or "production" mode) so there
  36 is no need to do this, unless the resources of the system your application will
  37 be running on are unusually constrained (notice that when asserts are disabled
  38 their condition is not even evaluated so the only run-time cost is a single
  39 condition check and the extra space taken by the asserts in the code).
  40
  41 This automatic deactivation of debugging code is done by IMPLEMENT_APP() macro
  42 so if you don't use you may need to explicitly call wxDISABLE_DEBUG_SUPPORT()
  43 yourself.
  44
  45 Also notice that it is possible to build your own application with a different
  46 value of wxDEBUG_LEVEL than the one which was used for wxWidgets itself. E.g.
  47 you may be using an official binary version of the library which will have been
  48 compiled with default @code wxDEBUG_LEVEL == 1 @endcode but still predefine
  49 wxDEBUG_LEVEL as 0 for your own code.
  50
  51 On the other hand, if you do want to keep the asserts even in production
  52 builds, you will probably want to override the handling of assertion failures
  53 as the default behaviour which pops up a message box notifying the user about
  54 the problem is usually inappropriate. Use wxSetAssertHandler() to set up your
  55 own custom function which should be called instead of the standard assertion
  56 failure handler. Such function could log an appropriate message in the
  57 application log file or maybe notify the user about the problem in some more
  58 user-friendly way.
  59
  60
  61
  62 @section overview_debugging_dbgmacros Assertion Macros
  63
  64 wxASSERT(), wxFAIL(), wxCHECK() as well as their other variants (see @ref
  65 group_funcmacro_debug) are similar to the standard assert() macro but are more
  66 flexible and powerful. The first of them is equivalent to assert() itself, i.e.
  67 it simply checks a condition and does nothing if it is true. The second one is
  68 equivalent to checking an always false condition and is supposed to be used for
  69 code paths which are supposed to be inaccessible (e.g. @c default branch of a
  70 @c switch statement which should never be executed). Finally, the wxCHECK()
  71 family of macros verifies the condition just as wxASSERT() does and performs
  72 some action such returning from the function if it fails -- thus, it is useful
  73 for checking the functions preconditions.
  74
  75 All of the above functions exist in @c _MSG variants which allow you to provide
  76 a custom message which will be shown (or, more generally, passed to the assert
  77 handler) if the assertion fails, in addition to the usual file and line number
  78 information and the condition itself.
  79
  80 Example of using an assertion macro:
  81 @code
  82 void GetTheAnswer(int *p)
  83 {
  84     wxCHECK_RET( p, "pointer can't be NULL in GetTheAnswer()" );
  85
  86     *p = 42;
  87 };
  88 @endcode
  89
  90 If the condition is false, i.e. @c p is @NULL, the assertion handler is called
  91 and, in any case (even when wxDEBUG_LEVEL is 0), the function returns without
  92 dereferencing the NULL pointer on the next line thus avoiding a crash.
  93
  94 The default assertion handler behaviour depends on whether the application
  95 using wxWidgets was compiled in release build (with @c NDEBUG defined) or debug
  96 one (without) but may be changed in either case as explained above. If it
  97 wasn't changed, then nothing will happen in the release build and a message box
  98 showing the information about the assert as well as allowing to stop the
  99 program, ignore future asserts or break into the debugger is shown. On the
 100 platforms where wxStackWalker is supported the message box will also show the
 101 stack trace at the moment when the assert failed often allowing you to diagnose
 102 the problem without using the debugger at all. You can see an example of such
 103 message box in the @ref page_samples_except.
 104
 105
 106
 107 @section overview_debugging_logging Logging Functions
 108
 109 You can use the wxLogDebug and wxLogTrace functions to output debugging
 110 information in debug mode; it will do nothing for non-debugging code.
 111
 112 */