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[wxWidgets.git] / docs / doxygen / overviews / exceptions.h

/////////////////////////////////////////////////////////////////////////////
// Name:        exceptions
// Purpose:     topic overview
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/*!

 @page exceptions_overview C++ exceptions overview

 #Introduction
 @ref exceptionstrategies_overview
 #Technicalities


 @section exceptionintroduction Introduction

 wxWidgets had been started long before the exceptions were introduced in C++ so
 it is not very surprising that it is not built around using them as some more
 modern C++ libraries are. For instance, the library doesn't throw exceptions to
 signal about the errors. Moreover, up to (and including) the version 2.4 of
 wxWidgets, even using the exceptions in the user code was dangerous because the
 library code wasn't exception-safe and so an exception propagating through it
 could result in memory and/or resource leaks, and also not very convenient.
 Starting from the version 2.5.1 wxWidgets becomes more exception-friendly. It
 still doesn't use the exceptions by itself but it should be now safe to use the
 exceptions in the user code and the library tries to help you with this. Please
 note that making the library exception-safe is still work in progress.


 @section exceptionstrategies Strategies for exceptions handling

 There are several choice for using the exceptions in wxWidgets programs. First
 of all, you may not use them at all. As stated above, the library doesn't throw
 any exceptions by itself and so you don't have to worry about exceptions at all
 unless your own code throws them. This is, of course, the simplest solution but
 may be not the best one to deal with all possible errors.
 Another strategy is to use exceptions only to signal truly fatal errors. In
 this case you probably don't expect to recover from them and the default
 behaviour -- to simply terminate the program -- may be appropriate. If it is
 not, you may override #OnUnhandledException()
 in your wxApp-derived class to perform any clean up tasks. Note, however, that
 any information about the exact exception type is lost when this function is
 called, so if you need you should override #OnRun() and
 add a try/catch clause around the call of the base class version. This would
 allow you to catch any exceptions generated during the execution of the main
 event loop. To deal with the exceptions which may arise during the program
 startup and/or shutdown you should insert try/catch clauses in
 #OnInit() and/or #OnExit() as well.
 Finally, you may also want to continue running even when certain exceptions
 occur. If all of your exceptions may happen only in the event handlers of a
 single class (or only in the classes derived from it), you may centralize your
 exception handling code in #ProcessEvent
 method of this class. If this is impractical, you may also consider overriding
 the wxApp::HandleEvent() which allows you to handle
 all the exceptions thrown by any event handler.


 @section exceptionstechnicalities Technicalities

 To use any kind of exception support in the library you need to build it with
 @c wxUSE_EXCEPTIONS set to 1. This should be the case by default but
 if it isn't, you should edit the @c include/wx/msw/setup.h file under
 Windows or run @c configure with @c --enable-exceptions argument
 under Unix.
 On the other hand, if you do not plan to use exceptions, setting this
 flag to 0 or using @c --disable-exceptions could result in a leaner and
 slightly faster library.
 As for any other library feature, there is a #sample
 showing how to use it. Please look at its sources for further information.

 */