docs/doxygen/overviews/exceptions.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        exceptions
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /*!
  10
  11  @page exceptions_overview C++ exceptions overview
  12
  13  #Introduction
  14  @ref exceptionstrategies_overview
  15  #Technicalities
  16
  17
  18  @section exceptionintroduction Introduction
  19
  20  wxWidgets had been started long before the exceptions were introduced in C++ so
  21  it is not very surprising that it is not built around using them as some more
  22  modern C++ libraries are. For instance, the library doesn't throw exceptions to
  23  signal about the errors. Moreover, up to (and including) the version 2.4 of
  24  wxWidgets, even using the exceptions in the user code was dangerous because the
  25  library code wasn't exception-safe and so an exception propagating through it
  26  could result in memory and/or resource leaks, and also not very convenient.
  27  Starting from the version 2.5.1 wxWidgets becomes more exception-friendly. It
  28  still doesn't use the exceptions by itself but it should be now safe to use the
  29  exceptions in the user code and the library tries to help you with this. Please
  30  note that making the library exception-safe is still work in progress.
  31
  32
  33  @section exceptionstrategies Strategies for exceptions handling
  34
  35  There are several choice for using the exceptions in wxWidgets programs. First
  36  of all, you may not use them at all. As stated above, the library doesn't throw
  37  any exceptions by itself and so you don't have to worry about exceptions at all
  38  unless your own code throws them. This is, of course, the simplest solution but
  39  may be not the best one to deal with all possible errors.
  40  Another strategy is to use exceptions only to signal truly fatal errors. In
  41  this case you probably don't expect to recover from them and the default
  42  behaviour -- to simply terminate the program -- may be appropriate. If it is
  43  not, you may override #OnUnhandledException()
  44  in your wxApp-derived class to perform any clean up tasks. Note, however, that
  45  any information about the exact exception type is lost when this function is
  46  called, so if you need you should override #OnRun() and
  47  add a try/catch clause around the call of the base class version. This would
  48  allow you to catch any exceptions generated during the execution of the main
  49  event loop. To deal with the exceptions which may arise during the program
  50  startup and/or shutdown you should insert try/catch clauses in
  51  #OnInit() and/or #OnExit() as well.
  52  Finally, you may also want to continue running even when certain exceptions
  53  occur. If all of your exceptions may happen only in the event handlers of a
  54  single class (or only in the classes derived from it), you may centralize your
  55  exception handling code in #ProcessEvent
  56  method of this class. If this is impractical, you may also consider overriding
  57  the wxApp::HandleEvent() which allows you to handle
  58  all the exceptions thrown by any event handler.
  59
  60
  61  @section exceptionstechnicalities Technicalities
  62
  63  To use any kind of exception support in the library you need to build it with
  64  @c wxUSE_EXCEPTIONS set to 1. This should be the case by default but
  65  if it isn't, you should edit the @c include/wx/msw/setup.h file under
  66  Windows or run @c configure with @c --enable-exceptions argument
  67  under Unix.
  68  On the other hand, if you do not plan to use exceptions, setting this
  69  flag to 0 or using @c --disable-exceptions could result in a leaner and
  70  slightly faster library.
  71  As for any other library feature, there is a #sample
  72  showing how to use it. Please look at its sources for further information.
  73
  74  */
  75
  76