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git.saurik.com Git - wxWidgets.git/blob - docs/doxygen/overviews/exceptions.h
1 /////////////////////////////////////////////////////////////////////////////
3 // Purpose: topic overview
4 // Author: wxWidgets team
5 // Licence: wxWindows licence
6 /////////////////////////////////////////////////////////////////////////////
10 @page overview_exceptions C++ Exceptions
14 wxWidgets had been started long before the exceptions were introduced in C++ so
15 it is not very surprising that it is not built around using them as some more
16 modern C++ libraries are. For instance, the library doesn't throw exceptions to
17 signal about the errors. Moreover, up to (and including) the version 2.4 of
18 wxWidgets, even using the exceptions in the user code was dangerous because the
19 library code wasn't exception-safe and so an exception propagating through it
20 could result in memory and/or resource leaks, and also not very convenient.
22 However the recent wxWidgets versions are exception-friendly. This means that
23 while the library still doesn't use the exceptions by itself, it should be now
24 safe to use the exceptions in the user code and the library tries to help you
29 @section overview_exceptions_strategies Strategies for Exception Handling
31 There are several choice for using the exceptions in wxWidgets programs. First
32 of all, you may not use them at all. As stated above, the library doesn't throw
33 any exceptions by itself and so you don't have to worry about exceptions at all
34 unless your own code throws them. This is, of course, the simplest solution but
35 may be not the best one to deal with all possible errors.
37 The next simplest strategy is to only use exceptions inside non-GUI code, i.e.
38 never let unhandled exceptions escape the event handler in which it happened.
39 In this case using exceptions in wxWidgets programs is not different from using
40 them in any other C++ program.
42 Things get more interesting if you decide to let (at least some) exceptions
43 escape from the event handler in which they occurred. Such exceptions will be
44 caught by wxWidgets and the special wxApp::OnExceptionInMainLoop() method will
45 be called from the @c catch clause. This allows you to decide in a single place
46 what to do about such exceptions: you may want to handle the exception somehow
47 or terminate the program. In this sense, OnExceptionInMainLoop() is equivalent
48 to putting a @c try/catch block around the entire @c main() function body in
49 the traditional console programs. However notice that, as its name indicates,
50 this method won't help you with the exceptions thrown before the main loop is
51 started or after it is over, so you may still want to have @c try/catch in your
52 overridden wxApp::OnInit() and wxApp::OnExit() methods too, otherwise
53 wxApp::OnUnhandledException() will be called.
55 Finally, notice that even if you decide to not let any exceptions escape in
56 this way, this still may happen unexpectedly in a program using exceptions as a
57 result of a bug. So consider always overriding OnExceptionInMainLoop() in your
58 wxApp-derived class if you use exceptions in your program, whether you expect
59 it to be called or not. In the latter case you may simple re-throw the
60 exception and let it bubble up to OnUnhandledException() as well.
62 To summarize, when you use exceptions in your code, you may handle them in the
63 following places, in order of priority:
64 -# In a @c try/catch block inside an event handler.
65 -# In wxApp::OnExceptionInMainLoop().
66 -# In wxApp::OnUnhandledException().
68 In the first two cases you may decide whether you want to handle the exception
69 and continue execution or to exit the program. In the last one the program is
70 about to exit already so you can just try to save any unsaved data and notify
71 the user about the problem (while being careful not to throw any more
72 exceptions as otherwise @c std::terminate() will be called).
75 @section overview_exceptions_tech Technicalities
77 To use any kind of exception support in the library you need to build it
78 with @c wxUSE_EXCEPTIONS set to 1. It is turned on by default but you may
79 wish to check @c include/wx/msw/setup.h file under Windows or run @c configure
80 with explicit @c --enable-exceptions argument under Unix.
82 On the other hand, if you do not plan to use exceptions, setting this
83 flag to 0 or using @c --disable-exceptions could result in a leaner and
84 slightly faster library.
86 As for any other library feature, there is a sample (@c except)
87 showing how to use it. Please look at its sources for further information.