X-Git-Url: https://git.saurik.com/wxWidgets.git/blobdiff_plain/98ba1eee5d1b107e66c9fd28963b95f46fdefe89..2e18fe7139558b3cb592a04a4e4668319a966ebf:/docs/doxygen/overviews/debugging.h diff --git a/docs/doxygen/overviews/debugging.h b/docs/doxygen/overviews/debugging.h index 948b4a5be0..d339b198a7 100644 --- a/docs/doxygen/overviews/debugging.h +++ b/docs/doxygen/overviews/debugging.h @@ -1,136 +1,112 @@ ///////////////////////////////////////////////////////////////////////////// // Name: debugging.h // Purpose: topic overview -// Author: wxWidgets team +// Author: Vadim Zeitlin +// Copyright: (c) 2009 Vadim Zeitlin // RCS-ID: $Id$ -// Licence: wxWindows license +// Licence: wxWindows licence ///////////////////////////////////////////////////////////////////////////// -/*! +/** + +@page overview_debugging Debugging + +Classes, functions and macros: wxLog, @ref group_funcmacro_log, @ref group_funcmacro_debug + +Various classes, functions and macros are provided in wxWidgets to help you debug +your application: @ref overview_debugging_dbgmacros allow you to insert various +checks in your application which can be compiled out or disabled in release +builds but are extremely useful while developing and @ref +overview_debugging_logging which are not limited to debugging but are also +useful for inserting traces into your application code. Both assertions and +debug logging are also used by wxWidgets itself so you may encounter them even +if you don't use either of these features yourself. + + +@section overview_debugging_config Configuring debugging support + +Starting with wxWidgets 2.9.1 debugging features are always available by +default (and not only in a special "debug" build of the library) and you need +to predefine wxDEBUG_LEVEL symbol as 0 when building both the library and your +application to remove them completely from the generated object code. However +the debugging features are disabled by default when the application itself is +built with @c NDEBUG defined (i.e. in "release" or "production" mode) so there +is no need to do this, unless the resources of the system your application will +be running on are unusually constrained (notice that when asserts are disabled +their condition is not even evaluated so the only run-time cost is a single +condition check and the extra space taken by the asserts in the code). + +This automatic deactivation of debugging code is done by IMPLEMENT_APP() macro +so if you don't use you may need to explicitly call wxDISABLE_DEBUG_SUPPORT() +yourself. + +Also notice that it is possible to build your own application with a different +value of wxDEBUG_LEVEL than the one which was used for wxWidgets itself. E.g. +you may be using an official binary version of the library which will have +been compiled with default @code wxDEBUG_LEVEL == 1 @endcode but still predefine +wxDEBUG_LEVEL as 0 for your own code. + +On the other hand, if you do want to keep the asserts even in production +builds, you will probably want to override the handling of assertion failures +as the default behaviour which pops up a message box notifying the user about +the problem is usually inappropriate. Use wxSetAssertHandler() to set up your +own custom function which should be called instead of the standard assertion +failure handler. Such function could log an appropriate message in the +application log file or maybe notify the user about the problem in some more +user-friendly way. + + +@section overview_debugging_dbgmacros Assertion macros + +wxASSERT(), wxFAIL(), wxCHECK() as well as their other variants (see @ref +group_funcmacro_debug) are similar to the standard assert() macro but are more +flexible and powerful. The first of them is equivalent to assert() itself, i.e. +it simply checks a condition and does nothing if it is true. The second one is +equivalent to checking an always false condition and is supposed to be used for +code paths which are supposed to be inaccessible (e.g. @c default branch of a +@c switch statement which should never be executed). Finally, the wxCHECK() +family of macros verifies the condition just as wxASSERT() does and performs +some action such returning from the function if it fails -- thus, it is useful +for checking the functions preconditions. + +All of the above functions exist in @c _MSG variants which allow you to provide +a custom message which will be shown (or, more generally, passed to the assert +handler) if the assertion fails, in addition to the usual file and line number +information and the condition itself. + +Example of using an assertion macro: +@code +void GetTheAnswer(int *p) +{ + wxCHECK_RET( p, "pointer can't be NULL in GetTheAnswer()" ); + + *p = 42; +}; +@endcode + +If the condition is false, i.e. @c p is @NULL, the assertion handler is called +and, in any case (even when wxDEBUG_LEVEL is 0), the function returns without +dereferencing the NULL pointer on the next line thus avoiding a crash. + +The default assertion handler behaviour depends on whether the application +using wxWidgets was compiled in release build (with @c NDEBUG defined) or debug +one (without) but may be changed in either case as explained above. If it +wasn't changed, then nothing will happen in the release build and a message box +showing the information about the assert as well as allowing to stop the +program, ignore future asserts or break into the debugger is shown. On the +platforms where wxStackWalker is supported the message box will also show the +stack trace at the moment when the assert failed often allowing you to diagnose +the problem without using the debugger at all. You can see an example of such +message box in the @ref page_samples_except. + + + +@section overview_debugging_logging Logging functions + +You can use the wxLogDebug and wxLogTrace functions to output debugging information in +debug mode; it will do nothing for non-debugging code. - @page overview_debugging Debugging overview - Classes, functions and macros: wxDebugContext, wxObject, wxLog, - @ref overview_logfunctions, @ref overview_debugmacros - - Various classes, functions and macros are provided in wxWidgets to help you debug - your application. Most of these are only available if you compile both wxWidgets, - your application and @e all libraries that use wxWidgets with the __WXDEBUG__ symbol - defined. You can also test the __WXDEBUG__ symbol in your own applications to execute - code that should be active only in debug mode. - - - - @section overview_debugging_dbgctx wxDebugContext - - wxDebugContext is a class that never gets instantiated, but ties together - various static functions and variables. It allows you to dump all objects to that stream, - write statistics about object allocation, and check memory for errors. - - It is good practice to define a wxObject::Dump member function for each class you derive - from a wxWidgets class, so that wxDebugContext::Dump can call it and - give valuable information about the state of the application. - - If you have difficulty tracking down a memory leak, recompile - in debugging mode and call wxDebugContext::Dump and wxDebugContext::PrintStatistics at - appropriate places. They will tell you what objects have not yet been - deleted, and what kinds of object they are. In fact, in debug mode wxWidgets will automatically - detect memory leaks when your application is about to exit, and if there are any leaks, - will give you information about the problem. (How much information depends on the operating system - and compiler -- some systems don't allow all memory logging to be enabled). See the - memcheck sample for example of usage. - - For wxDebugContext to do its work, the @e new and @e delete operators for wxObject - have been redefined to store extra information about dynamically allocated objects - (but not statically declared objects). - - This slows down a debugging version of an application, but can - find difficult-to-detect memory leaks (objects are not - deallocated), overwrites (writing past the end of your object) and - underwrites (writing to memory in front of the object). - - If debugging mode is on and the symbols wxUSE_GLOBAL_MEMORY_OPERATORS and - wxUSE_DEBUG_NEW_ALWAYS are set to 1 in setup.h, 'new' is defined to be: - - @code - #define new new(__FILE__,__LINE__) - @endcode - - All occurrences of 'new' in wxWidgets and your own application will use - the overridden form of the operator with two extra arguments. This means that - the debugging output (and error messages reporting memory problems) will tell you what - file and on what line you allocated the object. Unfortunately not all - compilers allow this definition to work properly, but most do. - - - - @section overview_debugging_dbgmacros Debug macros - - You should also use @ref debugmacros_overview as part of a 'defensive programming' strategy, - scattering wxASSERTs liberally to test for problems in your code as early as possible. - Forward thinking will save a surprising amount of time in the long run. - - #wxASSERT is used to pop up an error message box when a condition - is not @true. You can also use #wxASSERT_MSG to supply your - own helpful error message. For example: - - @code - void MyClass::MyFunction(wxObject* object) - { - wxASSERT_MSG( (object != NULL), "object should not be NULL in MyFunction!" ); - - ... - }; - @endcode - - The message box allows you to continue execution or abort the program. If you are running - the application inside a debugger, you will be able to see exactly where the problem was. - - - - @section overview_debugging_logging Logging functions - - You can use the #wxLogDebug and #wxLogTrace functions to output debugging information in - debug mode; it will do nothing for non-debugging code. - - - - @section overview_debugging_dbgctx2 wxDebugContext overview - - Class: wxDebugContext - - wxDebugContext is a class for performing various debugging and memory tracing operations. - - This class has only static data and function members, and there should be - no instances. Probably the most useful members are SetFile (for directing output - to a file, instead of the default standard error or debugger output); - Dump (for dumping the dynamically allocated objects) and PrintStatistics - (for dumping information about allocation of objects). You can also call - Check to check memory blocks for integrity. - - Here's an example of use. The SetCheckpoint ensures that only the - allocations done after the checkpoint will be dumped. - - @code - wxDebugContext::SetCheckpoint(); - - wxDebugContext::SetFile("c:\\temp\\debug.log"); - - wxString *thing = new wxString; - - char *ordinaryNonObject = new char[1000]; - - wxDebugContext::Dump(); - wxDebugContext::PrintStatistics(); - @endcode - - You can use wxDebugContext if __WXDEBUG__ is defined, or you can use it - at any other time (if wxUSE_DEBUG_CONTEXT is set to 1 in setup.h). It is not disabled - in non-debug mode because you may not wish to recompile wxWidgets and your entire application - just to make use of the error logging facility. - - @note wxDebugContext::SetFile has a problem at present, so use the default stream instead. - Eventually the logging will be done through the wxLog facilities instead. */