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3 <HEAD>
4 <TITLE>wxWidgets 2 for Windows FAQ</TITLE>
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13 <td bgcolor="#004080" align=left height=24 background="images/bluetitlegradient.gif">
14 <font size=+1 face="Arial, Lucida Sans, Helvetica" color="#FFFFFF">
15 <b>wxWidgets 2 for Windows FAQ</b>
16 </font>
17 </td>
18 </tr>
19 </table>
20
21 <P>
22
23 See also <a href="faq.htm">top-level FAQ page</a>.
24 <hr>
25 <h3>List of questions in this category</h3>
26 <ul>
27 <li><a href="#platforms">Which Windows platforms are supported?</a></li>
28 <li><a href="#wince">What about Windows CE?</a></li>
29 <li><a href="#winxp">What do I need to do for Windows XP?</a></li>
30 <li><a href="#compilers">What compilers are supported?</a></li>
31 <li><a href="#bestcompiler">Which is the best compiler to use with wxWidgets 2?</a></li>
32 <li><a href="#unicode">Is Unicode supported?</a></li>
33 <li><a href="#doublebyte">Does wxWidgets support double byte fonts (Chinese/Japanese/Korean etc.)?</a></li>
34 <li><a href="#dll">Can you compile wxWidgets 2 as a DLL?</a></li>
35 <li><a href="#exesize">How can I reduce executable size?</a></li>
36 <li><a href="#mfc">Is wxWidgets compatible with MFC?</a></li>
37 <li><a href="#setuph">Why do I get errors about setup.h not being found?</a></li>
38 <li><a href="#asuffix">Why do I get errors about FooBarA when I only use FooBar in my program?</a></li>
39 <li><a href="#newerrors">Why my code fails to compile with strange errors about new operator?</a></li>
40 <li><a href="#mfcport">How do I port MFC applications to wxWidgets?</a></li>
41 <li><a href="#crash">Why do I sometimes get bizarre crash problems using VC++ 5/6?</a></li>
42 <li><a href="#makefiles">How are the wxWidgets makefiles edited under Windows?</a></li>
43 <li><a href="#vcdebug">How do you use VC++&#39;s memory leak checking instead of that in wxWidgets?</a></li>
44 <li><a href="#shortcutproblem">Why are menu hotkeys or shortcuts not working in my application?</a></li>
45 <li><a href="#regconfig">Why can I not write to the HKLM part of the registry with wxRegConfig?</a></li>
46 <li><a href="#access">Is MS Active Accessibility supported?</a></li>
47 <li><a href="#dspfmt">Why does Visual C++ complain about corrupted project files??</a></li>
48 <li><a href="#crtmismatch">Visual C++ gives errors about multiply defined symbols, what can I do?</a></li>
49 <li><a href="#directx">Why do I get compilation erros when using wxWidgets with DirectShow?</a></li>
50 <li><a href="#handlewm">How do I handle Windows messages in my wxWidgets program?</a></li>
51 </ul>
52 <hr>
53
54 <h3><a name="platforms">Which Windows platforms are supported?</a></h3>
55
56 wxWidgets 2 can be used to develop and deliver applications on Windows 3.1, Win32s,
57 Windows 95, Windows 98, Windows NT, Windows 2000, and Windows XP. A Windows CE
58 version is being looked into (see below).<P>
59
60 wxWidgets 2 is designed to make use of WIN32 features and controls. However, unlike Microsoft,
61 we have not forgotten users of 16-bit Windows. Most features
62 work under Windows 3.1, including wxTreeCtrl and wxListCtrl using the generic implementation.
63 However, don&#39;t expect very Windows-95-specific classes to work, such as wxTaskBarIcon. The wxRegConfig
64 class doesn&#39;t work either because the Windows 3.1 registry is very simplistic. Check out the 16-bit
65 makefiles to see what other files have been left out.
66 <P>
67 16-bit compilation is supported under Visual C++ 1.5, and Borland BC++ 4 to 5.
68 <P>
69
70 wxWidgets 2 for Windows will also compile on Unix with gcc using Wine from <a href="http://www.winehq.org" target=_top>WineHQ</a>.
71 The resulting executables are Unix binaries that work with the Wine Windows API emulator.<P>
72
73 You can also compile wxWidgets 2 for Windows on Unix with Cygwin or Mingw32, resulting
74 in executables that will run on Windows. So in theory you could write your applications
75 using wxGTK or wxMotif, then check/debug your wxWidgets for Windows
76 programs with Wine, and finally produce an ix86 Windows executable using Cygwin/Mingw32,
77 without ever needing a copy of Microsoft Windows. See the Technical Note on the Web site detailing cross-compilation.<P>
78
79 <h3><a name="wince">What about Windows CE?</a></h3>
80
81 This port is largely complete. For further information, see the <a href="http://www.wxwidgets.org/embedded.htm#wxwince">wxEmbedded</a> page.<P>
82
83 <h3><a name="winxp">What do I need to do for Windows XP?</a></h3>
84
85 In the same directory as you have your executable (e.g. foo.exe) you
86 put a file called foo.exe.manifest in which you have something like
87 the following:
88
89 <pre>
90 &lt;?xml version="1.0" encoding="UTF-8" standalone="yes"?&gt;
91 &lt;assembly
92 xmlns="urn:schemas-microsoft-com:asm.v1"
93 manifestVersion="1.0"&gt;
94 &lt;assemblyIdentity
95 processorArchitecture="x86"
96 version="5.1.0.0"
97 type="win32"
98 name="foo.exe"/&gt;
99 &lt;description&gt;Foo program&lt;/description&gt;
100 &lt;dependency&gt;
101 &lt;dependentAssembly&gt;
102 &lt;assemblyIdentity
103 type="win32"
104 name="Microsoft.Windows.Common-Controls"
105 version="6.0.0.0"
106 publicKeyToken="6595b64144ccf1df"
107 language="*"
108 processorArchitecture="x86"/&gt;
109 &lt;/dependentAssembly&gt;
110 &lt;/dependency&gt;
111 &lt;/assembly&gt;
112 </pre>
113
114 If you want to add it to your application permanently,
115 you can also include it in your .rc file using this
116 line:<P>
117
118 <PRE>
119 1 24 "winxp.manifest"
120 </PRE>
121
122 In wxWidgets 2.5, this will be in the wx/msw/wx.rc and
123 so will happen automatically so long as you include wx.rc
124 in your own .rc file.<P>
125
126 For an explanation of this syntax, please see
127 <a href="http://delphi.about.com/library/bluc/text/uc111601a.htm" target=_new>this
128 article</a>.
129 <P>
130
131 <h3><a name="compilers">What compilers are supported?</a></h3>
132
133 Please see the wxWidgets 2 for Windows install.txt file for up-to-date information, but
134 currently the following are known to work:<P>
135
136 <ul>
137 <li>Visual C++ 1.5, 4.0, 5.0, 6.0, 7.0, 7.1
138 <li>Borland C++ 4.5, 5.0, 5.5
139 <li>Borland C++Builder 1.0, 3.0, X
140 <li>Watcom C++ 10.6 (Win32), OpenWatcom 1.0
141 <li>Cygwin (using configure)
142 <li>Mingw32
143 <li>MetroWerks CodeWarrior (many versions)
144 <li>Digital Mars 8.34+
145 </ul>
146 <P>
147
148
149 <h3><a name="bestcompiler">Which is the best compiler to use with wxWidgets 2?</a></h3>
150
151 It&#39;s partly a matter of taste, but I (JACS) prefer Visual C++ since the debugger is very
152 good, it&#39;s very stable, the documentation is extensive, and it generates small executables.
153 Since project files are plain text, it&#39;s easy for me to generate appropriate project files
154 for wxWidgets samples.<P>
155
156 Borland C++ is fine - and very fast - but it&#39;s hard (impossible?) to use the debugger without using project files, and
157 the debugger is nowhere near up to VC++&#39;s quality. The IDE isn&#39;t great.<P>
158
159 C++Builder&#39;s power isn&#39;t really used with wxWidgets since it needs integration with its
160 own class library (VCL). For wxWidgets, I&#39;ve only used it with makefiles, in which case
161 it&#39;s almost identical to BC++ 5.0 (the same makefiles can be used).<P>
162
163 You can&#39;t beat Cygwin&#39;s price (free), and you can debug adequately using gdb. However, it&#39;s
164 quite slow to compile since it does not use precompiled headers.<P>
165
166 CodeWarrior is cross-platform - you can debug and generate Windows executables from a Mac, but not
167 the other way around I think - but the IDE is, to my mind, a bit primitive.<P>
168
169 Watcom C++ is a little slow and the debugger is not really up to today&#39;s standards.<P>
170
171 Among the free compilers the best choice seem to be Borland C++ command line
172 tools and mingw32 (port of gcc to Win32). Both of them are supported by
173 wxWidgets.
174
175 <h3><a name="unicode">Is Unicode supported?</a></h3>
176
177 Yes, Unicode is fully supported under Windows NT/2000 and there is limited
178 support for it under Windows 9x using <a
179 href="http://www.microsoft.com/globaldev/handson/dev/mslu_announce.mspx">MSLU</a>.
180 <p>
181
182 <h3><a name="doublebyte">Does wxWidgets support double byte fonts (Chinese/Japanese/Korean etc.)?</a></h3>
183
184 For Japanese under Win2000, it seems that wxWidgets has no problems to work
185 with double byte char sets (meaning DBCS, not Unicode). First you have to
186 install Japanese support on your Win2K system and choose for ANSI translation
187 <tt>HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\CodePage=932</tt>
188 (default is 1252 for Western). Then you can see all the Japanese letters in
189 wxWidgets applications.
190 <p>
191
192 <h3><a name="dll">Can you compile wxWidgets 2 as a DLL?</a></h3>
193
194 Yes (using the Visual C++ or Borland C++ makefile), but be aware that distributing DLLs is a thorny issue
195 and you may be better off compiling statically-linked applications, unless you&#39;re
196 delivering a suite of separate programs, or you&#39;re compiling a lot of wxWidgets applications
197 and have limited hard disk space.<P>
198
199 With a DLL approach, and with different versions and configurations of wxWidgets
200 needing to be catered for, the end user may end up with a host of large DLLs in his or her Windows system directory,
201 negating the point of using DLLs. Of course, this is not a problem just associated with
202 wxWidgets!
203 <P>
204
205 <h3><a name="exesize">How can I reduce executable size?</a></h3>
206
207 You can compile wxWidgets as a DLL (see above, VC++/BC++ only at present). You should also
208 compile your programs for release using non-debugging and space-optimisation options, but
209 take with VC++ 5/6 space optimisation: it can sometimes cause problems.<P>
210
211 If you want to distribute really small executables, you can
212 use <a href="http://www.un4seen.com/petite/" target=_top>Petite</a>
213 by Ian Luck. This nifty utility compresses Windows executables by around 50%, so your 500KB executable
214 will shrink to a mere 250KB. With this sort of size, there is reduced incentive to
215 use DLLs. Another good compression tool (probably better than Petite) is <a href="http://upx.sourceforge.net/" target=_top>UPX</a>.
216 <P>
217
218 Please do not be surprised if MinGW produces a statically-linked minimal executable of 1 MB. Firstly, gcc
219 produces larger executables than some compilers. Secondly, this figure will
220 include most of the overhead of wxWidgets, so as your application becomes more
221 complex, the overhead becomes proportionally less significant. And thirdly, trading executable compactness
222 for the enormous increase in productivity you get with wxWidgets is almost always well worth it.<P>
223
224 If you have a really large executable compiled with MinGW (for example 20MB) then
225 you need to configure wxWidgets to compile without debugging information: see
226 docs/msw/install.txt for details. You may find that using configure instead
227 of makefile.g95 is easier, particularly since you can maintain debug and
228 release versions of the library simultaneously, in different directories.
229 Also, run &#39;strip&#39; after linking to remove all traces of debug info.
230 <P>
231
232 <H3><a name="mfc">Is wxWidgets compatible with MFC?</a></H3>
233
234 There is a sample which demonstrates MFC and wxWidgets code co-existing in the same
235 application. However, don&#39;t expect to be able to enable wxWidgets windows with OLE-2
236 functionality using MFC.<P>
237
238 <H3><a name="setuph">Why do I get errors about setup.h not being found?</a></H3>
239
240 When you build the wxWidgets library, setup.h is copied
241 from include/wx/msw/setup.h to e.g. lib/mswd/wx/setup.h (the path
242 depends on the configuration you&#39;re building). So you need to add
243 this include path if building using the static Debug library:<P>
244
245 lib/mswd<P>
246
247 or if building the static Release library, lib/msw.<P>
248
249 See also the <a href="http://wiki.wxwidgets.org/wiki.pl?Table_Of_Contents">wxWiki Contents</a>
250 for more information.<P>
251
252
253 <H3><a name="asuffix">Why do I get errors about FooBarA when I only use FooBar in my program?</H3>
254
255 If you get errors like
256 <p>
257 <center>
258 <tt>no matching function for call to &#39;wxDC::DrawTextA(const char[5], int,
259 int)&#39;</tt>
260 </center>
261 <p>
262 or similar ones for the other functions, i.e. the compiler error messages
263 mention the function with the <tt>&#39;A&#39;</tt> suffix while you didn&#39;t
264 use it in your code, the explanation is that you had included
265 <tt>&#60;windows.h&#062;</tt> header which redefines many symbols to have such
266 suffix (or <tt>&#39;W&#39;</tt> in the Unicode builds).
267
268 <p>
269 The fix is to either not include <tt>&#60;windows.h&#62;</tt> at all or include
270 <tt>"wx/msw/winundef.h"</tt> immediately after it.
271
272 <H3><a name="newerrors">Why my code fails to compile with strange errors about new operator?</a></H3>
273
274 The most common cause of this problem is the memory debugging settings in
275 <tt>wx/msw/setup.h</tt>. You have several choices:
276
277 <ul>
278 <li> Either disable overloading the global operator new completely by
279 setting <tt>wxUSE_GLOBAL_MEMORY_OPERATORS</tt> and
280 <tt>wxUSE_DEBUG_NEW_ALWAYS</tt> to 0 in this file
281 <li> Or leave them on but do <tt>#undef new</tt> after including any
282 wxWidgets headers, like this the memory debugging will be still on
283 for wxWidgets sources but off for your own code
284 </ul>
285
286 Notice that IMHO the first solution is preferable for VC++ users who can use
287 the <a href="#vcdebug">VC++ CRT memory debugging features</a> instead.
288
289 <H3><a name="mfcport">How do I port MFC applications to wxWidgets?</a></H3>
290
291 Set up your interface from scratch using wxWidgets (especially <a href="http://www.robeling.de" target=_top>wxDesigner</a>
292 or <a href="http://www.anthemion.co.uk/dialogblocks/" target=_new>DialogBlocks</a> --
293 it&#39;ll save you a <i>lot</i> of time) and when you have a shell prepared, you can start
294 &#39;pouring in&#39; code from the MFC app, with appropriate
295 modifications. This is the approach I have used, and I found
296 it very satisfactory. A two-step process then - reproduce the bare
297 interface first, then wire it up afterwards. That way you deal
298 with each area of complexity separately. Don&#39;t try to think MFC
299 and wxWidgets simultaneously from the beginning - it is easier to
300 reproduce the initial UI by looking at the behaviour of the MFC
301 app, not its code.
302
303 <H3><a name="crash">Why do I sometimes get bizarre crash problems using VC++ 5/6?</a></H3>
304
305 Some crash problems can be due to inconsistent compiler
306 options (and of course this isn&#39;t limited to wxWidgets).
307 If strange/weird/impossible things start to happen please
308 check (dumping IDE project file as makefile and doing text comparison
309 if necessary) that the project settings, especially the list of defined
310 symbols, struct packing, etc. are exactly the same for all items in
311 the project. After this, delete everything (including PCH) and recompile.<P>
312
313 VC++ 5&#39;s optimization code seems to be broken and can
314 cause problems: this can be seen when deleting an object Dialog
315 Editor, in Release mode with optimizations on. If in doubt,
316 switch off optimisations, although this will result in much
317 larger executables. It seems possible that the library can be created with
318 strong optimization, so long as the application is not strongly
319 optimized. For example, in wxWidgets project, set to &#39;Minimum
320 Size&#39;. In Dialog Editor project, set to &#39;Customize: Favor Small
321 Code&#39; (and no others). This will then work.<P>
322
323 <H3><a name="makefiles">How are the wxWidgets makefiles edited under Windows?</a></H3>
324
325 As of wxWidgets 2.1, there is a new system written by Vadim Zeitlin, that
326 generates the makefiles from templates using tmake.<P>
327
328 Here are Vadim&#39;s notes:<P>
329
330 <blockquote>
331 To use these new makefiles, you don&#39;t need anything (but see below).
332 However, you should NOT modify them because these files will be
333 rewritten when I regenerate them using tmake the next time. So, if
334 you find a problem with any of these makefiles (say, makefile.b32)
335 you&#39;ll need to modify the corresponding template (b32.t in this
336 example) and regenerate the makefile using tmake.<P>
337
338 tmake can be found at
339 <a href="http://www.troll.no/freebies/tmake.html" target=_new>www.troll.no/freebies/tmake.html</a>.
340 It&#39;s a Perl5 program and so it needs Perl (doh). There is a binary for
341 Windows (available from the same page), but I haven&#39;t used it, so
342 I don&#39;t know if it works as flawlessly as "perl tmake" does (note
343 for people knowing Perl: don&#39;t try to run tmake with -w, it won&#39;t
344 do you any good). Using it extremely simple: to regenerate makefile.b32
345 just go to distrib/msw/tmake and type<P>
346
347 <pre>tmake -t b32 wxwin.pro -o ../../src/msw/makefile.b32</pre><P>
348
349 The makefiles are untested - I don&#39;t have any of Borland, Watcom or
350 Symantec and I don&#39;t have enough diskspace to recompile even with
351 VC6 using makefiles. The new makefiles are as close as possible to the
352 old ones, but not closer: in fact, there has been many strange things
353 (should I say bugs?) in some of makefiles, some files were not compiled
354 without any reason etc. Please test them and notify me about any problems.
355 Better yet, modify the template files to generate the correct makefiles
356 and check them in.<P>
357
358 The templates are described in tmake ref manual (1-2 pages of text)
359 and are quite simple. They do contain some Perl code, but my Perl is
360 primitive (very C like) so it should be possible for anybody to make
361 trivial modifications to it (I hope that only trivial modifications
362 will be needed). I&#39;ve tagged the ol makefiles as MAKEFILES_WITHOUT_TMAKE
363 in the cvs, so you can always retrieve them and compare the new ones,
364 this will make it easier to solve the problems you might have.<P>
365
366 Another important file is filelist.txt: it contains the list of all
367 files to be compiled. Some of them are only compiled in 16/32 bit mode.
368 Some other are only compiled with some compilers (others can&#39;t compile
369 them) - all this info is contained in this file.<P>
370
371 So now adding a new file to wxWidgets is as easy as modifying filelist.txt
372 (and Makefile.ams for Unix ports) and regenerating the makefiles - no
373 need to modify all files manually any more.<P>
374
375 Finally, there is also a file vc6.t which I use myself: this one
376 generates a project file for VC++ 6.0 (I didn&#39;t create vc5.t because
377 I don&#39;t need it and can&#39;t test it, but it should be trivial to create
378 one from vc6.t - probably the only things to change would be the
379 version number in the very beginning and the /Z option - VC5 doesn&#39;t
380 support edit-and=continue). This is not an officially supported way
381 of building wxWidgets (that is, nobody guarantees that it will work),
382 but it has been very useful to me and I hope it will be also for
383 others. To generate wxWidgets.dsp run<P>
384
385 <pre>tmake -t vc6 wxwin.pro -o ../../wxWidgets.dsp</pre><P>
386
387 Then just include this project in any workspace or open it from VC IDE
388 and it will create a new workspace for you.<P>
389
390 If all goes well, I&#39;m planning to create a template file for Makefile.ams
391 under src/gtk and src/motif and also replace all makefiles in the samples
392 subdirectories with the project files from which all the others will be
393 generated. At least it will divide the number of files in samples
394 directory by 10 (and the number of files to be maintained too).
395 </blockquote>
396
397 <P>
398
399 <H3><a name="vcdebug">How do you use VC++&#39;s memory leak checking instead of that in wxWidgets?</a></H3>
400
401 Vadim Zeitlin:
402
403 <pre>
404 On the VC++ level, it&#39;s just the matter of calling _CrtSetDbgFlag() in the very
405 beginning of the program. In wxWidgets, this is done automatically when
406 compiling with VC++ in debug mode unless wxUSE_GLOBAL_MEMORY_OPERATORS or
407 __NO_VC_CRTDBG__ are defined - this check is done in wx/msw/msvcrt.h which
408 is included from app.cpp which then calls wxCrtSetDbgFlag() without any
409 ifdefs.
410
411 This works quite well: at the end of the program, all leaked blocks with their
412 malloc count are shown. This number (malloc count) can be used to determine
413 where exactly the object was allocated: for this it&#39;s enough to set the variable
414 _crtBreakAlloc (look in VC98\crt\srs\dbgheap.c line 326) to this number and
415 a breakpoint will be triggered when the block with this number is allocated.
416
417 For simple situations it works like a charm. For something more complicated
418 like reading uninitialized memory a specialized tool is probably better...
419
420 Regards,
421 VZ
422 </pre>
423
424 <P>
425
426 <H3><a name="shortcutproblem">Why are menu hotkeys or shortcuts not working in my application?</a></H3>
427
428 This can happen if you have a child window intercepting EVT_CHAR events and swallowing
429 all keyboard input. You should ensure that event.Skip() is called for all input that
430 isn&#39;used by the event handler.<P>
431
432 It can also happen if you append the submenu to the parent
433 menu {\it before} you have added your menu items. Do the append {\it after} adding
434 your items, or accelerators may not be registered properly.<P>
435
436 <H3><a name="#regconfig">Why can I not write to the HKLM part of the registry with wxRegConfig?</a></H3>
437
438 Currently this is not possible because the wxConfig family of classes is
439 supposed to deal with per-user application configuration data, and HKLM is
440 only supposed to be writeable by a user with Administrator privileges. In theory,
441 only installers should write to HKLM. This is still a point debated by the
442 wxWidgets developers. There are at least two ways to work around it if you really
443 need to write to HKLM.<P>
444
445 First, you can use wxRegKey directly, for example:
446
447 <pre>
448 wxRegKey regKey;
449
450 wxString idName(wxT("HKEY_LOCAL_MACHINE\\SOFTWARE\\My Company\\My Product\\Stuff\\"));
451 idName += packid;
452
453 regKey.SetName(idName);
454
455 {
456 wxLogNull dummy;
457 if (!regKey.Create())
458 {
459 idName = wxT("HKEY_CURRENT_USER\\SOFTWARE\\My Company\\My Product\\Stuff\\");
460 idName += packid;
461 regKey.SetName(idName);
462 if (!regKey.Create())
463 return FALSE;
464 }
465 }
466
467 if (!regKey.SetValue(wxT("THING"), (long) thing)) err += 1;
468
469 regKey.Close();
470
471 </pre>
472
473 Or, you can employ this trick suggested by Istvan Kovacs:
474
475 <pre>
476 class myGlobalConfig : public wxConfig
477 {
478 myGlobalConfig() :
479 wxConfig ("myApp", "myCompany", "", "", wxCONFIG_USE_GLOBAL_FILE)
480 {};
481 bool Write(const wxString& key, const wxString& value);
482 }
483
484 bool myGlobalConfig::Write (const wxString& key, const wxString& value)
485 {
486 wxString path = wxString ("SOFTWARE\\myCompany\\myApp\\") + wxPathOnly(key);
487 wxString new_path = path.Replace ("/", "\\", true);
488 wxString new_key = wxFileNameFromPath (key);
489 LocalKey().SetName (wxRegKey::HKLM, path);
490 return wxConfig::Write (new_key, value);
491 }
492 </pre>
493
494 <H3><a name="#access">Is MS Active Accessibility supported?</a></H3>
495
496 This is being worked on. Please see <a href="http://www.wxwidgets.org/access.htm">this page</a>
497 for the current status.
498
499 <P>
500
501
502 <h3><a name="#dspfmt">Why does Visual C++ complain about corrupted project files??</a></h3>
503
504 If you have downloaded the wxWidgets sources from the cvs using a Unix cvs
505 client or downloaded a daily snapshot in <tt>.tar.gz</tt> format, it is likely
506 that the project files have Unix line endings (LF) instead of the DOS ones (CR
507 LF). However all versions of Visual C++ up to and including 7.1 can only open
508 the files with the DOS line endings, so you must transform the files to this
509 format using any of the thousands ways to do it.
510 <p>
511 Of course, another possibility is to always use only the Windows cvs client
512 and to avoid this problem completely.
513 <p>
514
515 <h3><a name="#crtmismatch">Visual C++ gives errors about multiply defined symbols, what can I do?</a></h3>
516
517 If you get errors like this
518
519 <pre>
520 MSVCRTD.lib(MSVCRTD.dll) : error LNK2005: _xxxxxx already defined in LIBCD.lib(yyyyy.obj)
521 </pre>
522
523 when linking your project, this means that you used different versions of CRT
524 (C Run-Time) library for wxWindows (or possibly another library) and the main
525 project. Visual C++ provides static or dynamic and multithread safe or not
526 versions of CRT for each of debug and release builds, for a total of 8
527 libraries. You can choose among them by going to the "Code generation"
528 page/subitem of the "C++" tab/item in the project proprieties dialog in VC6/7.
529 <p>
530 To avoid problems, you <strong>must</strong> use the same one for all
531 components of your project. wxWindows uses multithread safe DLL version of the
532 CRT which is a good choice but may be problematic when distributing your
533 applications if you don&#39;t include the CRT DLL in your installation -- in this
534 case you may decide to switch to using a static CRT version. If you build with
535 <tt>wxUSE_THREADS == 0</tt> you may also use the non MT-safe version as it is
536 slightly smaller and faster.
537 <p>
538 But the most important thing is to use the <strong>same</strong> CRT setting for
539 all components of your project.
540
541 <h3><a name="#directx">Why do I get compilation erros when using wxWidgets with DirectShow?</a></h3>
542
543 If you get errors when including Microsoft DirectShow or DirectDraw headers,
544 the following message from Peter Whaite could help:
545 <blockquote>
546 &gt; This causes compilation errors within DirectShow:
547 &gt;
548 &gt; wxutil.h(125) : error C2065: &#39;EXECUTE_ASSERT&#39; : undeclared identifier
549 &gt; amfilter.h(1099) : error C2065: &#39;ASSERT&#39; : undeclared identifier
550
551 The reason for this is that __WXDEBUG__ is also used by the DXSDK (9.0
552 in my case) to &#39;#pragma once&#39; the contents of
553 DXSDK/Samples/C++/DirectShow/BaseClasses/wxdebug.h. So if __WXDEBUG__
554 is defined, then wxdebug.h doesn&#39;t get included, and the assert macros
555 don&#39;t get defined. You have to #undef __WXDEBUG__ before including the
556 directshow baseclass&#39;s &lt;streams.h&gt;.
557 </blockquote>
558
559
560 <h3><a name="#handlewm">How do I handle Windows messages in my wxWidgets program?</a></h3>
561
562 To handle a Windows message you need to override a virtual
563 <tt>MSWWindowProc()</tt> method in a wxWindow-derived class. You should then
564 test if <tt>nMsg</tt> parameter is the message you need to process and perform
565 the necessary action if it is or call the base class method otherwise.
566
567
568 </font>
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