docs/latex/wx/texcept.tex

   1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   2 %% Name:        texcept.tex
   3 %% Purpose:     C++ exceptions and wxWidgets overview
   4 %% Author:      Vadim Zeitlin
   5 %% Modified by:
   6 %% Created:     17.09.03
   7 %% RCS-ID:      $Id$
   8 %% Copyright:   (c) 2003 Vadim Zeitlin
   9 %% License:     wxWidgets license
  10 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  11
  12 \section{C++ exceptions overview}\label{exceptionsoverview}
  13
  14 \subsection{Introduction}\label{exceptionintroduction}
  15
  16 wxWidgets had been started long before the exceptions were introduced in C++ so
  17 it is not very surprising that it is not built around using them as some more
  18 modern C++ libraries are. For instance, the library doesn't throw exceptions to
  19 signal about the errors. Moreover, up to (and including) the version 2.4 of
  20 wxWidgets, even using the exceptions in the user code was dangerous because the
  21 library code wasn't exception-safe and so an exception propagating through it
  22 could result in memory and/or resource leaks, and also not very convenient.
  23
  24 Starting from the version 2.5.1 wxWidgets becomes more exception-friendly. It
  25 still doesn't use the exceptions by itself but it should be now safe to use the
  26 exceptions in the user code and the library tries to help you with this. Please
  27 note that making the library exception-safe is still work in progress.
  28
  29
  30 \subsection{Strategies for exceptions handling}\label{exceptionstrategies}
  31
  32 There are several choice for using the exceptions in wxWidgets programs. First
  33 of all, you may not use them at all. As stated above, the library doesn't throw
  34 any exceptions by itself and so you don't have to worry about exceptions at all
  35 unless your own code throws them. This is, of course, the simplest solution but
  36 may be not the best one to deal with all possible errors.
  37
  38 Another strategy is to use exceptions only to signal truly fatal errors. In
  39 this case you probably don't expect to recover from them and the default
  40 behaviour -- to simply terminate the program -- may be appropriate. If it is
  41 not, you may override \helpref{OnUnhandledException()}{wxapponunhandledexception}
  42 in your wxApp-derived class to perform any clean up tasks. Note, however, that
  43 any information about the exact exception type is lost when this function is
  44 called, so if you need you should override \helpref{OnRun()}{wxapponrun} and
  45 add a try/catch clause around the call of the base class version. This would
  46 allow you to catch any exceptions generated during the execution of the main
  47 event loop. To deal with the exceptions which may arise during the program
  48 startup and/or shutdown you should insert try/catch clauses in
  49 \helpref{OnInit()}{wxapponinit} and/or \helpref{OnExit()}{wxapponexit} as well.
  50
  51 Finally, you may also want to continue running even when certain exceptions
  52 occur. If all of your exceptions may happen only in the event handlers of a
  53 single class (or only in the classes derived from it), you may centralize your
  54 exception handling code in \helpref{ProcessEvent}{wxevthandlerprocessevent}
  55 method of this class. If this is impractical, you may also consider overriding
  56 the \helpref{wxApp::HandleEvent()}{wxapphandleevent} which allows you to handle
  57 all the exceptions thrown by any event handler.
  58
  59
  60 \subsection{Technicalities}\label{exceptionstechnicalities}
  61
  62 To use any kind of exception support in the library you need to build it with
  63 \texttt{wxUSE\_EXCEPTIONS} set to $1$. This should be the case by default but
  64 if it isn't, you should edit the \texttt{include/wx/msw/setup.h} file under
  65 Windows or run \texttt{configure} with \texttt{--enable-exceptions} argument
  66 under Unix.
  67
  68 On the other hand, if you do \emph{not} plan to use exceptions, setting this
  69 flag to $0$ or using \texttt{--disable-exceptions} could result in a leaner and
  70 slightly faster library.
  71
  72 As for any other library feature, there is a \helpref{sample}{sampleexcept}
  73 showing how to use it. Please look at its sources for further information.
  74
  75