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  16 wxWindows Programmer Style Guide
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  22 <P>
  23
  24 by <A HREF=mailto:zeitlin@dptmaths.ens-cachan.fr>Vadim Zeitlin</A><P>
  25
  26 This guide is intended for people who are (or intending to start) writing code
  27 for <A HREF="http://web.ukonline.co.uk/julian.smart/wxwin/" target=_top>wxWindows</A> class library.
  28
  29 <P>
  30 The guide is separated into two parts: the first one addresses the general
  31 compatibility issues and is not wxWindows-specific. The advises in this part
  32 will hopefully help you to write programs which compile and run on greater
  33 variety of platforms. The second part details the wxWindows code organization and
  34 its goal it to make wxWindows as uniform as possible without imposing too
  35 many restrictions on the programmer.
  36 <P>
  37 Acknowledgements: This guide is partly based on <A
  38 HREF=http://www.mozilla.org/docs/tplist/catBuild/portable-cpp.html target=_top>
  39 C++ portability guide</A> by David Williams.
  40
  41 <P>
  42 <H3>General C++ Rules</H3>
  43 <UL>
  44   <LI>New or not widely supported C++ features</LI>
  45   <OL>
  46     <LI><A HREF="#no_templates">Don't use C++ templates</A></LI>
  47     <LI><A HREF="#no_exceptions">Don't use C++ exceptions</A></LI>
  48     <LI><A HREF="#no_rtti">Don't use RTTI</A></LI>
  49     <LI><A HREF="#no_namespaces">Don't use namespaces</A></LI>
  50     <LI><A HREF="#no_stl">Don't use STL</A></LI>
  51     <LI><A HREF="#no_fordecl">Don't declare variables inside <TT>for()</TT></A></LI>
  52     <LI><A HREF="#no_nestedclasses">Don't use nested classes</A></LI>
  53   </OL>
  54   <BR>
  55   <LI>General recommendations</LI>
  56   <OL>
  57     <LI><A HREF="#no_globals">No global variables with constructor</A></LI>
  58     <LI><A HREF="#no_warnings">Turn on all warnings and eradicate them</A></LI>
  59     <LI><A HREF="#no_assume_sizeof">Don't rely on <TT>sizeof(int) == 2</TT>...</A></LI>
  60     <LI><A HREF="#no_assignment_in_if">No assignments in conditional expressions</A></LI>
  61     <LI><A HREF="#no_comment_code">Use <TT>#if 0</TT> rather than comments to temporarily
  62                     disable blocks of code</A></LI>
  63     <LI><A HREF="#no_extra_semicolon">Don't use extra semi-colons on top level</A></LI>
  64   </OL>
  65   <BR>
  66   <LI>Unix/DOS differences</LI>
  67   <OL>
  68     <LI><A HREF="#use_cpp_ext">Use .cpp for C++ source file extension</A></LI>
  69     <LI><A HREF="#no_backslash">Don't use backslash ('\\') in &#35;includes</A></LI>
  70     <LI><A HREF="#no_carriagereturn">Avoid carriage returns in cross-platform code</A></LI>
  71     <LI><A HREF="#no_caps_in_filenames">Use only lower letter filenames</A></LI>
  72     <LI><A HREF="#no_incomplete_files">Terminate the files with a new-line</A></LI>
  73   </OL>
  74   <BR>
  75   <LI>Style choices</LI>
  76   <OL>
  77     <LI><A HREF="#naming_conv">Naming conventions: use <TT>m_</TT> for members</A></LI>
  78     <LI><A HREF="#no_void_param">Don't use <TT>void</TT> for functions without
  79                     arguments</A></LI>
  80     <LI><A HREF="#no_const_int">Don't use <TT>const</TT> for non pointer/reference
  81                     arguments</A></LI>
  82   </OL>
  83 </UL>
  84
  85 <P>
  86
  87 <H3>wxWindows Rules</H3>
  88 <UL>
  89   <LI>Files location and naming conventions</LI>
  90   <OL>
  91     <LI><A HREF="#file_locations">File locations</A></LI>
  92     <LI><A HREF="#include_guards">Include guards</A></LI>
  93     <LI><A HREF="#pch">Precompiled headers</A></LI>
  94   </OL>
  95
  96   <BR>
  97   <LI>File layout and indentation</LI>
  98   <OL>
  99     <LI><A HREF="#wxwin_header">wxWindows standard header</A></LI>
 100     <LI><A HREF="#indentation">Indent your code with 4 spaces (no tabs!)</A></LI>
 101     <LI><A HREF="#class_decl">Order of parts in a class declarations</A></LI>
 102   </OL>
 103
 104   <BR>
 105   <LI>More about naming conventions</LI>
 106   <OL>
 107     <LI><A HREF="#wx_prefix">Use wx or WX prefix for all public symbols</A></LI>
 108     <LI><A HREF="#wxdllexport">Use WXDLLEXPORT with all classes/functions in
 109                                wxMSW/common code</A></LI>
 110     <LI><A HREF="#set_get">Use Set/Get prefixes for accessors</A></LI>
 111   </OL>
 112
 113   <BR>
 114   <LI>Miscellaneous</LI>
 115   <OL>
 116     <LI><A HREF="#forward_decl">Use forward declarations whenever possible</A></LI>
 117     <LI><A HREF="#debug_macros">Use debugging macros</A></LI>
 118   </OL>
 119 </UL>
 120
 121 <HR>
 122
 123 <H3>General C++ Rules</H3>
 124 <UL>
 125   <LI>New or not widely supported C++ features</LI>
 126
 127   <P>The usage of all features in this section is not recommended for one reason: they appeared in C++ relatively recently and are not yet
 128 supported by all compilers. Moreover, when they're supported, there are
 129 differences between different vendor's implementations. It's understandable that
 130 you might love one (or all) of these features, but you surely can write C++
 131 programs without them. Where possible, workarounds to compensate for absence
 132 of your favourite C++ abilities are indicated.
 133   <P>Just to suppress any doubts that there are compilers which don't support
 134 these new features, you can think about Win16 (a.k.a. Win 3.1) compilers,
 135 <I>none</I> of which supports <I>any</I> feature from the list below.
 136
 137   <OL>
 138     <P><LI><A NAME="no_templates"></A><B>Don't use C++ templates</B></LI><P>
 139 Besides the reasons mentioned above, template usage also makes the
 140 program compile much slower (200%-300% is not uncommon) and their support
 141 even in the compilers which have had it for a long time is far from perfect
 142 (the best example is probably gcc).
 143 <P><U>Workaround</U>: The things you would like to use templates for are,
 144 most commonly, polymorphic containers (in the sense that they can contain objects of
 145 any type without compromising C++ type system, i.e. using <TT>void *</TT>
 146 is out of question). wxWindows provides <A HREF="TODO">dynamic
 147 arrays and lists</A> which are sufficient in 99% of cases - please don't hesitate
 148 to use them. Lack of template is not a reason to use static arrays or
 149 type-less (passing by <TT>void *</TT>) containers.
 150
 151     <P><LI><A NAME="no_exceptions"></A><B>Don't use C++ exceptions</B></LI><P>
 152 The C++ exception system is an error-reporting mechanism. Another reasons not to use it,
 153 besides portability, are the performance penalty it imposes (small, but, at least for
 154 current compilers, non-zero), and subtle problems with
 155 memory/resource deallocation it may create (the place where you'd like to use
 156 C++ exceptions most of all are the constructors, but you need to be very
 157 careful in order to be able to do it).
 158 <P><U>Workaround</U>: there is no real workaround, of course, or the exceptions
 159 wouldn't have been added to the language. However, there are several rules which
 160 might help here:<P>
 161
 162 <OL>
 163   <LI>Every function returns an integer (or at least boolean) error code.
 164       <P>There is no such thing as a function that never fails - even if it can't
 165       fail now, it might do it later, when modified to be more powerful/general.
 166       Put the <TT>int</TT> or <TT>bool</TT> return type from the very beginning!<P>
 167   </LI><LI>Every function you call may fail - check the return code!
 168       <P>Never rely on the function's success, always test for a possible error.<P>
 169   </LI><LI>Tell the user about the error, don't silently ignore them.
 170       <P>Exceptions are always caught and, normally, processed when they're
 171       caught. In the same manner, the error return code must always be processed
 172       somehow. You may choose to ignore it, but at least tell the user that
 173       something wrong happened using <A HREF="TODO"><TT>wxLogError</TT></A> or
 174       <A HREF="TODO"><TT>wxLogWarning</TT></A> functions. All wxWindows
 175       functions (must) log the error messages on failure - this can be disabled
 176       by using <A HREF="TODO">wxLogNull</A> object before calling it.
 177       <P>Examples:<UL>
 178         <LI><I>Wrong</I>:
 179         <PRE>
 180 void ReadAddressBookFile(const wxString& strName)
 181 {
 182   wxFile file;
 183
 184   if ( !file.Open(strFile) )
 185     return;
 186
 187   ...process it...
 188 }
 189         </PRE>
 190         </LI><LI><I>Correct</I>:
 191         <PRE>
 192 // returns false if the address book couldn't be read
 193 bool ReadAddressBookFile(const wxString& strName)
 194 {
 195   wxFile file;
 196
 197   if ( !file.Open(strFile) ) {
 198     // wxFile logged an error because file couldn't be opened which
 199     // contains the system error code, however it doesn't know what
 200     // this file is for and an error message "can't open $GLCW.ADB"
 201     // can be quite confusing for the user. Here we say what we mean.
 202     wxLogError("Can't read address book from '%s'!",
 203                strName.c_str());
 204     return false;
 205   }
 206
 207   ...process it...
 208
 209   return true;
 210 }
 211         </PRE>
 212         or, if it's not an error if file doesn't exist (here we could just check
 213         its existence, but let's suppose that there is no <TT>wxFile::Exists()</TT>)
 214         we can also write:
 215         <PRE>
 216 // returns false if address book file doesn't exist
 217 bool ReadAddressBookFile(const wxString& strName)
 218 {
 219   wxFile file;
 220
 221   // start a block inside which all log messages are suppressed
 222   {
 223     wxLogNull noLog;
 224     if ( !file.Open(strFile) )
 225       return false;
 226   }
 227
 228   ...process it...
 229
 230   return true;
 231 }
 232         </PRE></LI>
 233     </UL>
 234   </OL>
 235
 236     <P><LI><A NAME="no_rtti"></A><B>Don't use RTTI</B></LI><P>
 237 RTTI stands for Run-Time Type Information and there is probably no other
 238 reason not to use it except the portability issue and the fact that it adds
 239 <TT>sizeof(void *)</TT> bytes to any class having virtual functions (at least,
 240 in the implementations I'm aware of).
 241 <P><U>Workaround</U>: use wxWindows RTTI system which allows you to do almost
 242 everything which the new C++ RTTI, except that, of course, you have to use
 243 macros instead of the (horrible looking, BTW) <TT>dynamic_cast</TT>.
 244
 245     <P><LI><A NAME="no_namespaces"></A><B>Don't use namespaces</B></LI><P>
 246 This topic is subject to change with time, however for the moment all wxWindows
 247 classes/functions live in the global namespace.
 248 <P><U>Workaround</U>: None.
 249
 250     <P><LI><A NAME="no_stl"></A><B>Don't use STL</B></LI><P>
 251 STL is the new C++ standard library, proposing all kinds of template containers
 252 and generic algorithm implementations. Templates are the heart (and almost
 253 everything else) of the library, so its usage is out of question. Besides, even
 254 with the compilers which do support templates, STL has many of its own problems,
 255 there are many "not 100% standard compatible" vendor implementations, none of existing debuggers understands its
 256 complicated data structures, ... the list can go on (almost) forever.
 257 <P><U>Workaround</U>: Use wxString, dynamic arrays and lists and other wxWindows
 258 classes. wxString has many of the most often used functions of std::string STL
 259 class (typedef to be precise).
 260     <P><LI><A NAME="no_fordecl"></A><B>Don't declare variables inside <TT>for()
 261                                        </TT></B></LI><P>
 262 The scope of a variable declared inside <TT>for()</TT> statement changed several
 263 years ago, however many compilers still will complain about second declaration
 264 of <TT>i</TT> in the following code:
 265 <PRE>
 266   for ( int i = 0; i < 10; i++ ) {
 267     ...
 268   }
 269
 270   ...
 271
 272   for ( int i = 0; i < 10; i++ ) {
 273     ...
 274   }
 275 </PRE>
 276 Even if it's perfectly legal now.
 277 <P><U>Workaround</U>: write this instead:
 278 <PRE>
 279   int i;
 280   for ( i = 0; i < 10; i++ ) {
 281     ...
 282   }
 283
 284   ...
 285
 286   for ( i = 0; i < 10; i++ ) {
 287     ...
 288   }
 289 </PRE>
 290
 291   <P><LI><A NAME="no_nestedclasses"></A><B>Don't use nested classes</B></LI><P>
 292 Nested classes are, without doubt, a very good thing because they allow to hide
 293 "private" (in the sense that they're used only inside the library) classes and,
 294 generally, put the related things together.
 295 <P>Unfortunately, some compilers have trouble understanding them, so we must
 296 sacrifice the ideals of software design to get a working program in this case.
 297 <P><U>Workaround</U>: instead of
 298 <PRE>
 299   // in the header
 300   class PublicLibClass {
 301   ...
 302   private:
 303     class PrivateLibClass { ... } m_object;
 304   };
 305 </PRE>
 306 you can try the following:
 307 <PRE>
 308   // in the header
 309   class PrivateLibClass; // fwd decl
 310   class PublicLibClass {
 311   ...
 312   private:
 313    class PrivateLibClass *m_pObject;
 314   };
 315
 316   // in the .cpp file
 317   class PrivateLibClass { ... };
 318
 319   PublicLibClass::PublicLibClass()
 320   {
 321     m_pObject = new PrivateLibClass;
 322
 323     ...
 324   }
 325
 326   PublicLibClass::~PublicLibClass()
 327   {
 328     delete m_pObject;
 329   }
 330 </PRE>
 331 <P>A nice side effect is that you don't need to recompile all the files
 332 including the header if you change the PrivateLibClass declaration (it's
 333 an example of a more general interface/implementation separation idea).
 334 </OL>
 335
 336   <BR>
 337   <LI>General recommendations</B></LI><P>
 338 While the recommendations in the previous section may not apply to you if you're
 339 only working with perfect compilers which implement the very newest directives of
 340 C++ standard, this section contains compiler- (and language-) independent advice
 341 which <B>must</B> be followed if you wish to write correct, i.e. working, programs. It
 342 also contains some C/C++ specific remarks in the end which are less
 343 important.
 344   <OL>
 345     <P><LI><A NAME="no_globals"></A><B>No global variables with constructors</B></LI><P>
 346 In C++, the constructors of global variables are called before the
 347 <TT>main()</TT> function (or <TT>WinMain()</TT> or any other program entry point)
 348 starts executing. Thus, there is no possibility to initialize <I>anything</I>
 349 before the constructor call. The order of construction is largely
 350 implementation-defined, meaning that there is no guarantee that one global
 351 object will be initialized before another one (except if they are both defined
 352 in the same translation unit, i.e. .cpp file). Most importantly, no custom
 353 memory allocation operators are installed at the moment of execution of global
 354 variables constructors, so a (less restrictive) rule is that you should have
 355 no global variables which allocate memory (or do anything else non-trivial) in
 356 the constructor. Of course, if an object doesn't allocate memory in its constructor
 357 right now, it may start making it later, so you can only be sure about this if
 358 you don't use <I>any</I> variables of object (as opposed to simple:
 359 <TT>int</TT>, ...) types. Example: currently, wxString doesn't allocate memory
 360 in its default constructor, so you might think that having a global (initially)
 361 empty wxString is safe. However, if wxString starts allocating some minimal
 362 amount of memory in its default constructor (which doesn't look unreasonable),
 363 you would have all kinds of problems with <TT>new</TT>
 364 and <TT>delete</TT> operators (overloaded in wxWindows), especially because the first <TT>new</TT> called
 365 is the standard one (before wxWindows overloads them) and <TT>delete</TT> will
 366 be the overloaded operator.
 367
 368     <P><LI><A NAME="no_warnings"></A><B>Turn on all warnings and eradicate them</B></LI><P>
 369 Give the compiler a chance to help you - turn on all warnings! You should always
 370 use the maximum available warning level of your compiler and understand and
 371 correct each of them. If, for whatever reasons, a compiler gives a warning on
 372 some perfectly legal line of code and you can't change it, please insert a
 373 comment indicating it in the code. Most oftenly, however, all compiler warnings
 374 may be avoided (not suppressed!) with minimal changes to your code.
 375
 376     <P><LI><A NAME="no_assume_sizeof"></A><B>Don't rely on <TT>sizeof(int) == 2</TT>...</B></LI><P>
 377 You should never assume any absolute constraints on data type sizes. Currently,
 378 we have 16-bit, 32-bit and 64-bit machines and even inside each class data type
 379 sizes are different. A small table illustrates it quite well:
 380 <TABLE BORDER COLS=5 WIDTH="100%" NOSAVE >
 381 <TR>
 382   <TD>Architecture/OS</TD>
 383   <TD>sizeof(short)</TD>
 384   <TD>sizeof(int)</TD>
 385   <TD>sizeof(long)</TD>
 386   <TD>sizeof(void *)</TD>
 387 </TR>
 388
 389 <TR>
 390   <TD>i386/Windows 3.1</TD>
 391   <TD>2</TD>
 392   <TD>2</TD>
 393   <TD>4</TD>
 394   <TD>2 or 4</TD>
 395 </TR>
 396
 397 <TR>
 398   <TD>i386/Windows 95</TD>
 399   <TD>2</TD>
 400   <TD>4</TD>
 401   <TD>4</TD>
 402   <TD>4</TD>
 403 </TR>
 404
 405 <TR>
 406   <TD>Merced/Win64</TD>
 407   <TD>2</TD>
 408   <TD>4</TD>
 409   <TD>4</TD>
 410   <TD>8</TD>
 411 </TR>
 412
 413 <TR>
 414   <TD>Alpha/Linux</TD>
 415   <TD>???</TD>
 416   <TD>???</TD>
 417   <TD>???</TD>
 418   <TD>???</TD>
 419 </TR>
 420 </TABLE>
 421
 422     <P><LI><A NAME="no_assignment_in_if"></A><B>No assignments in conditional expressions</B></LI><P>
 423 Although close to the heart of many C programmers (I plead guilty), code like
 424 classical <TT>if ( (c = getchar()) != EOF )</TT> is bad because it prevents you
 425 from enabling "assignment in conditional expression" warning (see also
 426 <A HREF="#no_warnings">above</A>) warning which is helpful to detect common
 427 mistypes like <TT>if ( x = 2 )</TT> instead of <TT>if ( x == 2 )</TT>.
 428
 429     <P><LI><A NAME="no_comment_code"></A><B>Use <TT>#if 0</TT> rather than comments to temporarily
 430                     disable blocks of code</B></LI><P>
 431 If you have to temporarily disable some code, use
 432 <PRE>
 433   #if 0 // VZ: I think this code is unneeded, it probably must be removed
 434     ...
 435   #endif // 0
 436 </PRE>
 437 instead of
 438 <PRE>
 439   /*
 440     ...
 441   */
 442 </PRE>
 443 The reason is simple: if there are any <TT>/* ... */</TT> comments inside
 444 <TT>...</TT> the second version will, of course, miserably fail.
 445
 446     <P><LI><A NAME="no_extra_semicolon"></A><B>Don't use extra semi-colons on top level</B></LI><P>
 447 Some compilers don't pay any attention to extra semicolons on top level, as in
 448 <PRE>
 449   class Foo { };;
 450 </PRE>
 451 while others complain loudly about it. Of course, you would rarely put 2
 452 semicolons yourself, but it may happen if you're using a macro
 453 (<TT>IMPLEMENT_something</TT>, for example) which already has a ';' inside and
 454 put another one after it.
 455   </OL>
 456
 457   <BR>
 458   <LI>Unix/DOS differences</B></LI><P>
 459   Two operating systems supported by wxWindows right now are (different flavours
 460 of) Unix and Windows 3.1/95/NT (although Mac, OS/2 and other ports exist/are
 461 being developed as well). The main differences between them are summarized
 462 here.
 463
 464   <OL>
 465     <P><LI><A NAME="use_cpp_ext"></A><B>Use .cpp for C++ source file extension</B></LI><P>
 466 There is, unfortunately, no standard exceptions for C++ source files. Different
 467 people use .C, .cc, .cpp, .cxx, .c++ and probably several others I forgot. Some
 468 compilers don't care about extension, but there are also other ones which can't
 469 be made to compile any file with "wrong" extension. Such compilers are very
 470 common in DOS/Windows land, that's why the .cpp extension is the least likely to
 471 cause any problems - it's the standard one under DOS and will probably be
 472 accepted by any Unix compiler as well (any counter examples?). The extension
 473 for the header files is .h.
 474
 475     <P><LI><A NAME="no_backslash"></A><B>Don't use backslash ('\\') in &#35;includes</B></LI><P>
 476 Although it's too silly to mention, please don't use backslashes in
 477 <TT>&#35;include</TT> preprocessor statement. Even not all Windows compilers accept
 478 it, without speaking about all other ones.
 479
 480     <P><LI><A NAME="no_carriagereturn"></A><B>Avoid carriage returns in cross-platform code</B></LI><P>
 481 This problem will hopefully not arise at all, with CVS taking care of this
 482 stuff, however it's perhaps not useless to remember that many Unix compilers
 483 (including, but not limited to, gcc) don't accept carriage returns
 484 (= <Ctrl-M> = '\r') in C/C++ code.
 485
 486     <P><LI><A NAME="no_caps_in_filenames"></A><B>Use only lower case filenames</B></LI><P>
 487 DOS/Windows 3.1 isn't case sensitive, Windows 95/NT are case preserving, but not
 488 case sensitive. To avoid all kinds of problems with compiling under Unix (or
 489 any other fully case-sensitive OS), please use only lower case letters in the
 490 filenames.
 491
 492     <P><LI><A NAME="no_incomplete_files"></A><B>Terminate the files with a new-line</B></LI><P>
 493 While DOS/Windows compilers don't seem to mind, their Unix counterparts don't
 494 like files without terminating new-line. Such files also give a warning message
 495 when loaded to vim (the Unix programmer's editor of choice :-)), so please think
 496 about terminating the last line.
 497   </OL>
 498
 499   <BR>
 500   <LI>Style choices</B></LI><P>
 501   All wxWindows specific style guidelines are specified in the next
 502 section, here are the choices which are not completely arbitrary,
 503 but have some deeper and not wxWindows-specific meaning.
 504
 505   <OL>
 506     <P><LI><A NAME="naming_conv"></A><B>Naming conventions: use <TT>m_</TT> for members</B></LI><P>
 507 It's extremely important to write readable code. One of the first steps in this
 508 direction is the choice of naming convention. It may be quite vague or strictly
 509 define the names of all the variables and function in the program, however it
 510 surely must somehow allow the reader to distinguish between variable and
 511 functions and local variables and member variables from the first glance.
 512 <P>The first requirement is commonly respected, but for some strange reasons, the
 513 second isn't, even if it's much more important because, after all, the immediate
 514 context usually allows you to distinguish a variable from a function in
 515 C/C++ code. On the other hand, you <I>cannot</I> say what <TT>x</TT> in the
 516 following code fragment is:
 517 <PRE>
 518   void Foo::Bar(int x_)
 519   {
 520     ...
 521
 522     x = x_;
 523
 524     ...
 525   }
 526 </PRE>
 527 It might be either a local variable (unluckily the function is too long so you
 528 don't see the variable declarations when you look at <TT>x = x_</TT> line), a
 529 member variable or a global variable - you have no way of knowing.
 530 <P>The wxWindows naming convention gives you, the reader of the code, much more
 531 information about <TT>x</TT>. In the code above you know that it's a local
 532 variable because:<P>
 533 <OL>
 534   <LI>global variables are always prefixed with <TT>g_</TT></LI>
 535   <LI>member variables are always prefixed with <TT>m_</TT></LI>
 536   <LI>static variables are always prefixed with <TT>s_</TT></LI>
 537 </OL>
 538 <P>Examples:
 539 <PRE>
 540   extern int g_x; // of course, 'x' is not the best name for a global...
 541
 542   void Bar()
 543   {
 544     int x;
 545   }
 546
 547   class Foo {
 548     public:
 549       void SetX(int x) { m_x = x; }
 550     private:
 551       int m_x;
 552   };
 553 </PRE>
 554 As you see, it also solves once and for all the old C++ programmer's question:
 555 how to call <TT>SetX()</TT> parameter? The answer is simple: just call it
 556 <TT>x</TT> because there is no ambiguity with <TT>Foo::m_x</TT>.
 557 <P>The prefixes can be combined to give <TT>ms_</TT> and <TT>gs_</TT> for static
 558 member (a.k.a. class) variables and static global variables.
 559 <P>The convention is, of course, completely worthless if it is not followed:
 560 nothing like being sure that <TT>x</TT> is a local variable in the code fragment
 561 above and discovering later the following lines in the header:
 562 <PRE>
 563   class Foo {
 564     ...
 565     int x;  // I don't like wxWindows naming convention
 566   };
 567 </PRE>
 568 Please do use these prefixes, they make your code much easier to read. Also
 569 please notice that it has nothing to do with the so-called <I>Hungarian notation</I>
 570 which is used in wxMSW part of wxWindows code and which encodes the <I>type</I>
 571 of the variable in its name - it is actually quite useful in C, but has little
 572 or no sense in C++.
 573
 574     <P><LI><A NAME="no_void_param"></A><B>Don't use <TT>void</TT> for functions without
 575                     arguments</B></LI><P>
 576 In ANSI C, <TT>void Foo()</TT> takes an arbitrary number of arbitrarily typed
 577 arguments (although the form <TT>void Foo(...)</TT> is preferred) and <TT>void
 578 Foo(void)</TT> doesn't take any arguments. In C++, however, the situation is
 579 different and both declarations are completely equivalent. As there is no need
 580 to write <TT>void</TT> in this situation, let's not write it - it can only be
 581 confusing and create an impression that it really means something when it's not
 582 at all the case.
 583
 584     <P><LI><A NAME="no_const_int"></A><B>Don't use <TT>const</TT> for non pointer/reference
 585                     arguments</B></LI><P>
 586 In both C and C++ an argument passed by value cannot be modified - or, more
 587 precisely, if it is modified in the called function, only the local copy is
 588 really changed, not the caller's variable. So, semantically speaking, there is
 589 no difference between <TT>void Foo(int)</TT> and <TT>void Foo(const int)</TT>.
 590 However, the <TT>const</TT> keyword is confusing here, adds nothing to the code
 591 and even cannot be removed if <TT>Foo()</TT> is virtual and overridden (because
 592 the names are mangled differently). So, <I>for arguments passed by value</I>
 593 you shouldn't use <TT>const</TT>.
 594 <P>Of course, it doesn't apply to functions such as
 595 <TT>void PrintMessage(const char *text)</TT> where <TT>const</TT> is mandatory.
 596   </OL>
 597 </UL>
 598
 599 <P>
 600
 601 <H3>wxWindows rules</H3>
 602 <UL>
 603   <P><LI>File location and naming conventions</LI><P>
 604   <OL>
 605     <P><LI><A NAME="file_locations"></LI><B>File locations</B><P>
 606 The wxWindows files for each supported platform have their own subdirectories
 607 in "include" and "src". So, for example, there is "src/msw", "include/gtk"
 608 etc. There are also two special subdirectories called "common" and
 609 "generic". The common subdirectory contains the files which are platform
 610 independent (wxObject, wxString, ...) and the generic one the generic
 611 implementations of GUI widgets, i.e. those which use only other wxWindows
 612 classes to implement them. For the platforms where the given functionality
 613 cannot be implemented natively, the generic implementation is used and the native
 614 one is used for the others. As I feel that it becomes a bit too confusing,
 615 here is an example: wxMessageBox function is implemented natively under
 616 Windows (where it just calls MessageBox API), but there is also a generic
 617 implementation which is used under, for example, GTK. A generic class should
 618 normally have a name that distinguishes it from any platform-specific implementation.
 619 A #define will allow wxGenericMessageDialog to be wxMessageDialog on some
 620 platforms, for example.
 621
 622 <P>This scheme applies not only for the .cpp files, but also for the headers.
 623 However, as the program using wxWindows should (ideally) not use any
 624 "<TT>&#35;ifdef &lt;platform&gt;</TT>" at all, the headers are always included with
 625 "<TT>&#35;include &lt;wx/msgdlg.h&gt;</TT>" (for example). This file, in turn, includes
 626 the right header for given platform. Any new headers should conform to this
 627 setup as well to allow including <TT>&lt;wx/foo.h&gt;</TT> on any platform.<P>
 628
 629 Note that wxWindows implementation files should use quotes when including wxWindows
 630 headers, not angled brackets. Applications should use angled brackets. There
 631 is a reason for it (can anyone remember what this is?).
 632
 633     <P><LI><A NAME="include_guards"></LI><B>Include guards</B><P>
 634 To minimize the compile time C++ programmers often use so called include
 635 guards: for example, in the header file foo.h you might have
 636
 637 <PRE>
 638 &#35;ifndef _FOO_H_
 639 &#35;define _FOO_H_
 640
 641 ... all header contents ...
 642
 643 &#35;endif
 644  //_FOO_H_
 645 </PRE>
 646
 647 In this way, the header will only be included once for the compilation
 648 of any .cpp (of course, it still will be included many times for the
 649 compilation of the whole project, so it has nothing to do with precompiled
 650 headers). wxWindows is no exception and also uses include guards which should use
 651 the above form, except for top-level headers which include files with identical
 652 names, in which case you should use _FOO_H_BASE_.
 653
 654     <P><LI><A NAME="pch"></LI><B>Precompiled headers</B><P>
 655 The precompiled headers greatly (we're speaking about orders of hundreds of
 656 percent here) reduce the compilation time. wxWindows uses them if the target
 657 compiler supports them (it knows about MS Visual C++, Borland C++ and g++).
 658 You should include all the headers included from <TT><wx/wx_prec.h></TT> only
 659 inside "<TT>&#35;if !USE_PRECOMP</TT>" to avoid unnecessary overhead in the case
 660 when the precompiled headers are used.<P>
 661
 662 The start of a cpp implementation file after the heading might look like this:<P>
 663
 664 <PRE>
 665 &#35;ifdef __GNUG__
 666 &#35;pragma implementation "bitmap.h"
 667 &#35;endif
 668
 669 // For compilers that support precompilation, includes "wx.h".
 670 &#35;include "wx/wxprec.h"
 671
 672 &#35;ifdef __BORLANDC__
 673 &#35;pragma hdrstop
 674 &#35;endif
 675
 676 &#35;ifndef WX_PRECOMP
 677 &#35;include &lt;stdio.h&gt;
 678 &#35;include "wx/setup.h"
 679 &#35;include "wx/list.h"
 680 &#35;include "wx/utils.h"
 681 &#35;include "wx/app.h"
 682 &#35;include "wx/palette.h"
 683 &#35;include "wx/bitmap.h"
 684 &#35;include "wx/icon.h"
 685 &#35;endif
 686
 687 &#35;include "wx/msw/private.h"
 688 &#35;include "assert.h"
 689 </PRE>
 690
 691
 692 <P>Any header file should containg the following lines:
 693 <PRE>
 694 &#35;ifdef __GNUG__
 695   &#35;pragma interface "foo.h"
 696 &#35;endif
 697 </PRE>
 698 and the corresponding .cpp file:
 699 <PRE>
 700 &#35;ifdef __GNUG__
 701   &#35;pragma  implementation "foo.h"
 702 &#35;endif
 703 </PRE> for g++ compilation.
 704   </OL>
 705
 706   <P><LI>File layout and indentation</LI><P>
 707   <OL>
 708     <P><LI><A NAME="wxwin_header"></LI><B>wxWindows standard header</B> <a href="header.txt">here</a>. The
 709 copyright holder is the original author. It is assumed the author does not assert copyright,
 710 under the terms of the wxWindows licence. This is a legal interpretation of the informal
 711 usage 'public domain' (the copyright holder does not assert the copyright).<P>
 712     <P><LI><A NAME="indentation"></LI><B>Indent your code with 4 spaces (no tabs!)</B>
 713     <P><LI><A NAME="class_decl"></LI><B>Order of parts in a class declarations</B><P>
 714   </OL>
 715
 716   <P><LI>More about naming conventions</LI><P>
 717   <OL>
 718     <P><LI><A NAME="wx_prefix"></LI><B>Use wx or WX prefix for all public symbols</B>.
 719 wx should be used for functions and classes, WX for macros.
 720     <P><LI><A NAME="wxdllexport"</LI><B>Use WXDLLEXPORT with all classes/functions in
 721                                 wxMSW/common code</B>
 722 The title says it all - every public (in the sense that it is not internal to
 723 the library) function or class should have WXDLLEXPORT macro in its
 724 declaration to allow compilation of wxWindows as shared library. For example:<P>
 725
 726 <pre>
 727 bool WXDLLEXPORT wxYield(void);
 728 class WXDLLEXPORT MyClass;  // (for forward declarations and real declarations)
 729 WXDLLEXPORT_DATA(extern wxApp*) wxTheApp;
 730 </pre>
 731
 732 The reason for the strange syntax for data is that some compilers use different
 733 keyword ordering for exporting data.
 734
 735 <P>There also several other places where you should take care of shared
 736 library case: all IMPLEMENT_xxx macros which are usually used in the
 737 corresponding .cpp files must be taken inside
 738 "<TT>&#35;if !USE_SHARED_LIBRARY</TT>" and in the <TT>&#35;if USE_SHARED_LIBRARY</TT>
 739 case you should put them inside <TT>common/cmndata.cpp</TT> file.
 740
 741     <P><LI><A NAME="set_get"></LI><B>Use Set/Get prefixes for accessors</B><P>
 742 There is a convention in wxWindows to prefix the accessors (i.e. any simple, in
 743 general, inline function which does nothing else except changing or returning
 744 the value of a member variable) with either <TT>Set</TT> or <TT>Get</TT>.
 745   </OL>
 746
 747   <P><LI>Miscellaneous</LI><P>
 748   <OL>
 749     <P><LI><A NAME="forward_decl"></LI><B>Use forward declarations whenever possible</B><P>
 750 It's really a trivial piece of advice, but remember that using forward declarations
 751 instead of including the header of corresponding class is better because not
 752 only does it minimize the compile time, it also simplifies the dependencies
 753 between different source files.
 754 <P>On a related subject, in general, you should try not to include other
 755 headers from a header file.
 756
 757     <P><LI><A NAME="debug_macros"></LI><B>Use debugging macros</B><P>
 758 wxWindows provides the debugging macros <TT>wxASSERT, wxFAIL</TT> and
 759 <TT>wxCHECK_RET</TT> in <TT><wx/wx.h></TT> file. Please use them as often as
 760 you can - they will never do you any harm but can greatly simplify the bug
 761 tracking both for you and for others.
 762 <P>Also, please use <TT>wxFAIL_MSG("not implemented")</TT> instead of writing
 763 stubs for not (yet) implemented functions which silently return incorrect
 764 values - otherwise, a person using a not implemented function has no idea that
 765 it is, in fact, not implemented.
 766 <P>As all debugging macros only do something useful if the symbol
 767 <TT>__DEBUG__</TT> is defined, you should compile your programs in debug mode to profit
 768 from them.
 769   </OL>
 770 </UL>
 771
 772 <P>
 773
 774 <HR>
 775 Please send any comments to <A HREF=mailto:zeitlin@dptmaths.ens-cachan.fr>Vadim Zeitlin</A>.
 776
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