dbd94b7501
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30072 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
76 lines
3.9 KiB
TeX
76 lines
3.9 KiB
TeX
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%% Name: texcept.tex
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%% Purpose: C++ exceptions and wxWidgets overview
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%% Author: Vadim Zeitlin
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%% Modified by:
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%% Created: 17.09.03
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%% RCS-ID: $Id$
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%% Copyright: (c) 2003 Vadim Zeitlin
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%% License: wxWidgets license
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{C++ exceptions overview}\label{exceptionsoverview}
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\subsection{Introduction}\label{exceptionintroduction}
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wxWidgets had been started long before the exceptions were introduced in C++ so
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it is not very surprising that it is not built around using them as some more
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modern C++ libraries are. For instance, the library doesn't throw exceptions to
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signal about the errors. Moreover, up to (and including) the version 2.4 of
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wxWidgets, even using the exceptions in the user code was dangerous because the
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library code wasn't exception-safe and so an exception propagating through it
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could result in memory and/or resource leaks, and also not very convenient.
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Starting from the version 2.5.1 wxWidgets becomes more exception-friendly. It
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still doesn't use the exceptions by itself but it should be now safe to use the
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exceptions in the user code and the library tries to help you with this. Please
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note that making the library exception-safe is still work in progress.
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\subsection{Strategies for exceptions handling}\label{exceptionstrategies}
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There are several choice for using the exceptions in wxWidgets programs. First
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of all, you may not use them at all. As stated above, the library doesn't throw
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any exceptions by itself and so you don't have to worry about exceptions at all
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unless your own code throws them. This is, of course, the simplest solution but
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may be not the best one to deal with all possible errors.
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Another strategy is to use exceptions only to signal truly fatal errors. In
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this case you probably don't expect to recover from them and the default
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behaviour -- to simply terminate the program -- may be appropriate. If it is
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not, you may override \helpref{OnUnhandledException()}{wxapponunhandledexception}
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in your wxApp-derived class to perform any clean up tasks. Note, however, that
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any information about the exact exception type is lost when this function is
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called, so if you need you should override \helpref{OnRun()}{wxapponrun} and
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add a try/catch clause around the call of the base class version. This would
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allow you to catch any exceptions generated during the execution of the main
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event loop. To deal with the exceptions which may arise during the program
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startup and/or shutdown you should insert try/catch clauses in
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\helpref{OnInit()}{wxapponinit} and/or \helpref{OnExit()}{wxapponexit} as well.
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Finally, you may also want to continue running even when certain exceptions
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occur. If all of your exceptions may happen only in the event handlers of a
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single class (or only in the classes derived from it), you may centralize your
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exception handling code in \helpref{ProcessEvent}{wxevthandlerprocessevent}
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method of this class. If this is impractical, you may also consider overriding
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the \helpref{wxApp::HandleEvent()}{wxapphandleevent} which allows you to handle
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all the exceptions thrown by any event handler.
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\subsection{Technicalities}\label{exceptionstechnicalities}
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To use any kind of exception support in the library you need to build it with
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\texttt{wxUSE\_EXCEPTIONS} set to $1$. This should be the case by default but
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if it isn't, you should edit the \texttt{include/wx/msw/setup.h} file under
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Windows or run \texttt{configure} with \texttt{--enable-exceptions} argument
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under Unix.
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On the other hand, if you do \emph{not} plan to use exceptions, setting this
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flag to $0$ or using \texttt{--disable-exceptions} could result in a leaner and
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slightly faster library.
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As for any other library feature, there is a \helpref{sample}{sampleexcept}
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showing how to use it. Please look at its sources for further information.
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