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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     <LI><A HREF="#constants">wxNAMING_CONSTANTS</A></LI>
 112   </OL>
 113
 114   <BR>
 115   <LI>Miscellaneous</LI>
 116   <OL>
 117     <LI><A HREF="#forward_decl">Use forward declarations whenever possible</A></LI>
 118     <LI><A HREF="#debug_macros">Use debugging macros</A></LI>
 119   </OL>
 120 </UL>
 121
 122 <HR>
 123
 124 <H3>General C++ Rules</H3>
 125 <UL>
 126   <LI>New or not widely supported C++ features</LI>
 127
 128   <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
 129 supported by all compilers. Moreover, when they're supported, there are
 130 differences between different vendor's implementations. It's understandable that
 131 you might love one (or all) of these features, but you surely can write C++
 132 programs without them. Where possible, workarounds to compensate for absence
 133 of your favourite C++ abilities are indicated.
 134   <P>Just to suppress any doubts that there are compilers which don't support
 135 these new features, you can think about Win16 (a.k.a. Win 3.1) compilers,
 136 <I>none</I> of which supports <I>any</I> feature from the list below.
 137
 138   <OL>
 139     <P><LI><A NAME="no_templates"></A><B>Don't use C++ templates</B></LI><P>
 140 Besides the reasons mentioned above, template usage also makes the
 141 program compile much slower (200%-300% is not uncommon) and their support
 142 even in the compilers which have had it for a long time is far from perfect
 143 (the best example is probably gcc).
 144 <P><U>Workaround</U>: The things you would like to use templates for are,
 145 most commonly, polymorphic containers (in the sense that they can contain objects of
 146 any type without compromising C++ type system, i.e. using <TT>void *</TT>
 147 is out of question). wxWindows provides <A HREF="TODO">dynamic
 148 arrays and lists</A> which are sufficient in 99% of cases - please don't hesitate
 149 to use them. Lack of template is not a reason to use static arrays or
 150 type-less (passing by <TT>void *</TT>) containers.
 151
 152     <P><LI><A NAME="no_exceptions"></A><B>Don't use C++ exceptions</B></LI><P>
 153 The C++ exception system is an error-reporting mechanism. Another reasons not to use it,
 154 besides portability, are the performance penalty it imposes (small, but, at least for
 155 current compilers, non-zero), and subtle problems with
 156 memory/resource deallocation it may create (the place where you'd like to use
 157 C++ exceptions most of all are the constructors, but you need to be very
 158 careful in order to be able to do it).
 159 <P><U>Workaround</U>: there is no real workaround, of course, or the exceptions
 160 wouldn't have been added to the language. However, there are several rules which
 161 might help here:<P>
 162
 163 <OL>
 164   <LI>Every function returns an integer (or at least boolean) error code.
 165       <P>There is no such thing as a function that never fails - even if it can't
 166       fail now, it might do it later, when modified to be more powerful/general.
 167       Put the <TT>int</TT> or <TT>bool</TT> return type from the very beginning!<P>
 168   </LI><LI>Every function you call may fail - check the return code!
 169       <P>Never rely on the function's success, always test for a possible error.<P>
 170   </LI><LI>Tell the user about the error, don't silently ignore them.
 171       <P>Exceptions are always caught and, normally, processed when they're
 172       caught. In the same manner, the error return code must always be processed
 173       somehow. You may choose to ignore it, but at least tell the user that
 174       something wrong happened using <A HREF="TODO"><TT>wxLogError</TT></A> or
 175       <A HREF="TODO"><TT>wxLogWarning</TT></A> functions. All wxWindows
 176       functions (must) log the error messages on failure - this can be disabled
 177       by using <A HREF="TODO">wxLogNull</A> object before calling it.
 178       <P>Examples:<UL>
 179         <LI><I>Wrong</I>:
 180         <PRE>
 181 void ReadAddressBookFile(const wxString& strName)
 182 {
 183   wxFile file;
 184
 185   if ( !file.Open(strFile) )
 186     return;
 187
 188   ...process it...
 189 }
 190         </PRE>
 191         </LI><LI><I>Correct</I>:
 192         <PRE>
 193 // returns false if the address book couldn't be read
 194 bool ReadAddressBookFile(const wxString& strName)
 195 {
 196   wxFile file;
 197
 198   if ( !file.Open(strFile) ) {
 199     // wxFile logged an error because file couldn't be opened which
 200     // contains the system error code, however it doesn't know what
 201     // this file is for and an error message "can't open $GLCW.ADB"
 202     // can be quite confusing for the user. Here we say what we mean.
 203     wxLogError("Can't read address book from '%s'!",
 204                strName.c_str());
 205     return false;
 206   }
 207
 208   ...process it...
 209
 210   return true;
 211 }
 212         </PRE>
 213         or, if it's not an error if file doesn't exist (here we could just check
 214         its existence, but let's suppose that there is no <TT>wxFile::Exists()</TT>)
 215         we can also write:
 216         <PRE>
 217 // returns false if address book file doesn't exist
 218 bool ReadAddressBookFile(const wxString& strName)
 219 {
 220   wxFile file;
 221
 222   // start a block inside which all log messages are suppressed
 223   {
 224     wxLogNull noLog;
 225     if ( !file.Open(strFile) )
 226       return false;
 227   }
 228
 229   ...process it...
 230
 231   return true;
 232 }
 233         </PRE></LI>
 234     </UL>
 235   </OL>
 236
 237     <P><LI><A NAME="no_rtti"></A><B>Don't use RTTI</B></LI><P>
 238 RTTI stands for Run-Time Type Information and there is probably no other
 239 reason not to use it except the portability issue and the fact that it adds
 240 <TT>sizeof(void *)</TT> bytes to any class having virtual functions (at least,
 241 in the implementations I'm aware of).
 242 <P><U>Workaround</U>: use wxWindows RTTI system which allows you to do almost
 243 everything which the new C++ RTTI, except that, of course, you have to use
 244 macros instead of the (horrible looking, BTW) <TT>dynamic_cast</TT>.
 245
 246     <P><LI><A NAME="no_namespaces"></A><B>Don't use namespaces</B></LI><P>
 247 This topic is subject to change with time, however for the moment all wxWindows
 248 classes/functions live in the global namespace.
 249 <P><U>Workaround</U>: None.
 250
 251     <P><LI><A NAME="no_stl"></A><B>Don't use STL</B></LI><P>
 252 STL is the new C++ standard library, proposing all kinds of template containers
 253 and generic algorithm implementations. Templates are the heart (and almost
 254 everything else) of the library, so its usage is out of question. Besides, even
 255 with the compilers which do support templates, STL has many of its own problems,
 256 there are many "not 100% standard compatible" vendor implementations, none of existing debuggers understands its
 257 complicated data structures, ... the list can go on (almost) forever.
 258 <P><U>Workaround</U>: Use wxString, dynamic arrays and lists and other wxWindows
 259 classes. wxString has many of the most often used functions of std::string STL
 260 class (typedef to be precise).
 261     <P><LI><A NAME="no_fordecl"></A><B>Don't declare variables inside <TT>for()
 262                                        </TT></B></LI><P>
 263 The scope of a variable declared inside <TT>for()</TT> statement changed several
 264 years ago, however many compilers still will complain about second declaration
 265 of <TT>i</TT> in the following code:
 266 <PRE>
 267   for ( int i = 0; i < 10; i++ ) {
 268     ...
 269   }
 270
 271   ...
 272
 273   for ( int i = 0; i < 10; i++ ) {
 274     ...
 275   }
 276 </PRE>
 277 Even if it's perfectly legal now.
 278 <P><U>Workaround</U>: write this instead:
 279 <PRE>
 280   int i;
 281   for ( i = 0; i < 10; i++ ) {
 282     ...
 283   }
 284
 285   ...
 286
 287   for ( i = 0; i < 10; i++ ) {
 288     ...
 289   }
 290 </PRE>
 291
 292   <P><LI><A NAME="no_nestedclasses"></A><B>Don't use nested classes</B></LI><P>
 293 Nested classes are, without doubt, a very good thing because they allow to hide
 294 "private" (in the sense that they're used only inside the library) classes and,
 295 generally, put the related things together.
 296 <P>Unfortunately, some compilers have trouble understanding them, so we must
 297 sacrifice the ideals of software design to get a working program in this case.
 298 <P><U>Workaround</U>: instead of
 299 <PRE>
 300   // in the header
 301   class PublicLibClass {
 302   ...
 303   private:
 304     class PrivateLibClass { ... } m_object;
 305   };
 306 </PRE>
 307 you can try the following:
 308 <PRE>
 309   // in the header
 310   class PrivateLibClass; // fwd decl
 311   class PublicLibClass {
 312   ...
 313   private:
 314    class PrivateLibClass *m_pObject;
 315   };
 316
 317   // in the .cpp file
 318   class PrivateLibClass { ... };
 319
 320   PublicLibClass::PublicLibClass()
 321   {
 322     m_pObject = new PrivateLibClass;
 323
 324     ...
 325   }
 326
 327   PublicLibClass::~PublicLibClass()
 328   {
 329     delete m_pObject;
 330   }
 331 </PRE>
 332 <P>A nice side effect is that you don't need to recompile all the files
 333 including the header if you change the PrivateLibClass declaration (it's
 334 an example of a more general interface/implementation separation idea).
 335 </OL>
 336
 337   <BR>
 338   <LI>General recommendations</B></LI><P>
 339 While the recommendations in the previous section may not apply to you if you're
 340 only working with perfect compilers which implement the very newest directives of
 341 C++ standard, this section contains compiler- (and language-) independent advice
 342 which <B>must</B> be followed if you wish to write correct, i.e. working, programs. It
 343 also contains some C/C++ specific remarks in the end which are less
 344 important.
 345   <OL>
 346     <P><LI><A NAME="no_globals"></A><B>No global variables with constructors</B></LI><P>
 347 In C++, the constructors of global variables are called before the
 348 <TT>main()</TT> function (or <TT>WinMain()</TT> or any other program entry point)
 349 starts executing. Thus, there is no possibility to initialize <I>anything</I>
 350 before the constructor call. The order of construction is largely
 351 implementation-defined, meaning that there is no guarantee that one global
 352 object will be initialized before another one (except if they are both defined
 353 in the same translation unit, i.e. .cpp file). Most importantly, no custom
 354 memory allocation operators are installed at the moment of execution of global
 355 variables constructors, so a (less restrictive) rule is that you should have
 356 no global variables which allocate memory (or do anything else non-trivial) in
 357 the constructor. Of course, if an object doesn't allocate memory in its constructor
 358 right now, it may start making it later, so you can only be sure about this if
 359 you don't use <I>any</I> variables of object (as opposed to simple:
 360 <TT>int</TT>, ...) types. Example: currently, wxString doesn't allocate memory
 361 in its default constructor, so you might think that having a global (initially)
 362 empty wxString is safe. However, if wxString starts allocating some minimal
 363 amount of memory in its default constructor (which doesn't look unreasonable),
 364 you would have all kinds of problems with <TT>new</TT>
 365 and <TT>delete</TT> operators (overloaded in wxWindows), especially because the first <TT>new</TT> called
 366 is the standard one (before wxWindows overloads them) and <TT>delete</TT> will
 367 be the overloaded operator.
 368
 369     <P><LI><A NAME="no_warnings"></A><B>Turn on all warnings and eradicate them</B></LI><P>
 370 Give the compiler a chance to help you - turn on all warnings! You should always
 371 use the maximum available warning level of your compiler and understand and
 372 correct each of them. If, for whatever reasons, a compiler gives a warning on
 373 some perfectly legal line of code and you can't change it, please insert a
 374 comment indicating it in the code. Most oftenly, however, all compiler warnings
 375 may be avoided (not suppressed!) with minimal changes to your code.
 376
 377     <P><LI><A NAME="no_assume_sizeof"></A><B>Don't rely on <TT>sizeof(int) == 2</TT>...</B></LI><P>
 378 You should never assume any absolute constraints on data type sizes. Currently,
 379 we have 16-bit, 32-bit and 64-bit machines and even inside each class data type
 380 sizes are different. A small table illustrates it quite well:
 381 <TABLE BORDER COLS=5 WIDTH="100%" NOSAVE >
 382 <TR>
 383   <TD>Architecture/OS</TD>
 384   <TD>sizeof(short)</TD>
 385   <TD>sizeof(int)</TD>
 386   <TD>sizeof(long)</TD>
 387   <TD>sizeof(void *)</TD>
 388 </TR>
 389
 390 <TR>
 391   <TD>i386/Windows 3.1</TD>
 392   <TD>2</TD>
 393   <TD>2</TD>
 394   <TD>4</TD>
 395   <TD>2 or 4</TD>
 396 </TR>
 397
 398 <TR>
 399   <TD>i386/Windows 95</TD>
 400   <TD>2</TD>
 401   <TD>4</TD>
 402   <TD>4</TD>
 403   <TD>4</TD>
 404 </TR>
 405
 406 <TR>
 407   <TD>Merced/Win64</TD>
 408   <TD>2</TD>
 409   <TD>4</TD>
 410   <TD>4</TD>
 411   <TD>8</TD>
 412 </TR>
 413
 414 <TR>
 415   <TD>Alpha/Linux</TD>
 416   <TD>???</TD>
 417   <TD>???</TD>
 418   <TD>???</TD>
 419   <TD>???</TD>
 420 </TR>
 421 </TABLE>
 422
 423     <P><LI><A NAME="no_assignment_in_if"></A><B>No assignments in conditional expressions</B></LI><P>
 424 Although close to the heart of many C programmers (I plead guilty), code like
 425 classical <TT>if ( (c = getchar()) != EOF )</TT> is bad because it prevents you
 426 from enabling "assignment in conditional expression" warning (see also
 427 <A HREF="#no_warnings">above</A>) which is helpful to detect common
 428 mistypes like <TT>if ( x = 2 )</TT> instead of <TT>if ( x == 2 )</TT>.
 429
 430     <P><LI><A NAME="no_comment_code"></A><B>Use <TT>#if 0</TT> rather than comments to temporarily
 431                     disable blocks of code</B></LI><P>
 432 If you have to temporarily disable some code, use
 433 <PRE>
 434   #if 0 // VZ: I think this code is unneeded, it probably must be removed
 435     ...
 436   #endif // 0
 437 </PRE>
 438 instead of
 439 <PRE>
 440   /*
 441     ...
 442   */
 443 </PRE>
 444 The reason is simple: if there are any <TT>/* ... */</TT> comments inside
 445 <TT>...</TT> the second version will, of course, miserably fail.
 446
 447     <P><LI><A NAME="no_extra_semicolon"></A><B>Don't use extra semi-colons on top level</B></LI><P>
 448 Some compilers don't pay any attention to extra semicolons on top level, as in
 449 <PRE>
 450   class Foo { };;
 451 </PRE>
 452 while others complain loudly about it. Of course, you would rarely put 2
 453 semicolons yourself, but it may happen if you're using a macro
 454 (<TT>IMPLEMENT_something</TT>, for example) which already has a ';' inside and
 455 put another one after it.
 456   </OL>
 457
 458   <BR>
 459   <LI>Unix/DOS differences</B></LI><P>
 460   Two operating systems supported by wxWindows right now are (different flavours
 461 of) Unix and Windows 3.1/95/NT (although Mac, OS/2 and other ports exist/are
 462 being developed as well). The main differences between them are summarized
 463 here.
 464
 465   <OL>
 466     <P><LI><A NAME="use_cpp_ext"></A><B>Use .cpp for C++ source file extension</B></LI><P>
 467 There is, unfortunately, no standard exceptions for C++ source files. Different
 468 people use .C, .cc, .cpp, .cxx, .c++ and probably several others I forgot. Some
 469 compilers don't care about extension, but there are also other ones which can't
 470 be made to compile any file with "wrong" extension. Such compilers are very
 471 common in DOS/Windows land, that's why the .cpp extension is the least likely to
 472 cause any problems - it's the standard one under DOS and will probably be
 473 accepted by any Unix compiler as well (any counter examples?). The extension
 474 for the header files is .h.
 475
 476     <P><LI><A NAME="no_backslash"></A><B>Don't use backslash ('\\') in &#35;includes</B></LI><P>
 477 Although it's too silly to mention, please don't use backslashes in
 478 <TT>&#35;include</TT> preprocessor statement. Even not all Windows compilers accept
 479 it, without speaking about all other ones.
 480
 481     <P><LI><A NAME="no_carriagereturn"></A><B>Avoid carriage returns in cross-platform code</B></LI><P>
 482 This problem will hopefully not arise at all, with CVS taking care of this
 483 stuff, however it's perhaps not useless to remember that many Unix compilers
 484 (including, but not limited to, gcc) don't accept carriage returns
 485 (= <Ctrl-M> = '\r') in C/C++ code.
 486
 487     <P><LI><A NAME="no_caps_in_filenames"></A><B>Use only lower case filenames</B></LI><P>
 488 DOS/Windows 3.1 isn't case sensitive, Windows 95/NT are case preserving, but not
 489 case sensitive. To avoid all kinds of problems with compiling under Unix (or
 490 any other fully case-sensitive OS), please use only lower case letters in the
 491 filenames.
 492
 493     <P><LI><A NAME="no_incomplete_files"></A><B>Terminate the files with a new-line</B></LI><P>
 494 While DOS/Windows compilers don't seem to mind, their Unix counterparts don't
 495 like files without terminating new-line. Such files also give a warning message
 496 when loaded to vim (the Unix programmer's editor of choice :-)), so please think
 497 about terminating the last line.
 498   </OL>
 499
 500   <BR>
 501   <LI>Style choices</B></LI><P>
 502   All wxWindows specific style guidelines are specified in the next
 503 section, here are the choices which are not completely arbitrary,
 504 but have some deeper and not wxWindows-specific meaning.
 505
 506   <OL>
 507     <P><LI><A NAME="naming_conv"></A><B>Naming conventions: use <TT>m_</TT> for members</B></LI><P>
 508 It's extremely important to write readable code. One of the first steps in this
 509 direction is the choice of naming convention. It may be quite vague or strictly
 510 define the names of all the variables and function in the program, however it
 511 surely must somehow allow the reader to distinguish between variable and
 512 functions and local variables and member variables from the first glance.
 513 <P>The first requirement is commonly respected, but for some strange reasons, the
 514 second isn't, even if it's much more important because, after all, the immediate
 515 context usually allows you to distinguish a variable from a function in
 516 C/C++ code. On the other hand, you <I>cannot</I> say what <TT>x</TT> in the
 517 following code fragment is:
 518 <PRE>
 519   void Foo::Bar(int x_)
 520   {
 521     ...
 522
 523     x = x_;
 524
 525     ...
 526   }
 527 </PRE>
 528 It might be either a local variable (unluckily the function is too long so you
 529 don't see the variable declarations when you look at <TT>x = x_</TT> line), a
 530 member variable or a global variable - you have no way of knowing.
 531 <P>The wxWindows naming convention gives you, the reader of the code, much more
 532 information about <TT>x</TT>. In the code above you know that it's a local
 533 variable because:<P>
 534 <OL>
 535   <LI>global variables are always prefixed with <TT>g_</TT></LI>
 536   <LI>member variables are always prefixed with <TT>m_</TT></LI>
 537   <LI>static variables are always prefixed with <TT>s_</TT></LI>
 538 </OL>
 539 <P>Examples:
 540 <PRE>
 541   extern int g_x; // of course, 'x' is not the best name for a global...
 542
 543   void Bar()
 544   {
 545     int x;
 546   }
 547
 548   class Foo {
 549     public:
 550       void SetX(int x) { m_x = x; }
 551     private:
 552       int m_x;
 553   };
 554 </PRE>
 555 As you see, it also solves once and for all the old C++ programmer's question:
 556 how to call <TT>SetX()</TT> parameter? The answer is simple: just call it
 557 <TT>x</TT> because there is no ambiguity with <TT>Foo::m_x</TT>.
 558 <P>The prefixes can be combined to give <TT>ms_</TT> and <TT>gs_</TT> for static
 559 member (a.k.a. class) variables and static global variables.
 560 <P>The convention is, of course, completely worthless if it is not followed:
 561 nothing like being sure that <TT>x</TT> is a local variable in the code fragment
 562 above and discovering later the following lines in the header:
 563 <PRE>
 564   class Foo {
 565     ...
 566     int x;  // I don't like wxWindows naming convention
 567   };
 568 </PRE>
 569 Please do use these prefixes, they make your code much easier to read. Also
 570 please notice that it has nothing to do with the so-called <I>Hungarian notation</I>
 571 which is used in wxMSW part of wxWindows code and which encodes the <I>type</I>
 572 of the variable in its name - it is actually quite useful in C, but has little
 573 or no sense in C++.
 574
 575     <P><LI><A NAME="no_void_param"></A><B>Don't use <TT>void</TT> for functions without
 576                     arguments</B></LI><P>
 577 In ANSI C, <TT>void Foo()</TT> takes an arbitrary number of arbitrarily typed
 578 arguments (although the form <TT>void Foo(...)</TT> is preferred) and <TT>void
 579 Foo(void)</TT> doesn't take any arguments. In C++, however, the situation is
 580 different and both declarations are completely equivalent. As there is no need
 581 to write <TT>void</TT> in this situation, let's not write it - it can only be
 582 confusing and create an impression that it really means something when it's not
 583 at all the case.
 584
 585     <P><LI><A NAME="no_const_int"></A><B>Don't use <TT>const</TT> for non pointer/reference
 586                     arguments</B></LI><P>
 587 In both C and C++ an argument passed by value cannot be modified - or, more
 588 precisely, if it is modified in the called function, only the local copy is
 589 really changed, not the caller's variable. So, semantically speaking, there is
 590 no difference between <TT>void Foo(int)</TT> and <TT>void Foo(const int)</TT>.
 591 However, the <TT>const</TT> keyword is confusing here, adds nothing to the code
 592 and even cannot be removed if <TT>Foo()</TT> is virtual and overridden (because
 593 the names are mangled differently). So, <I>for arguments passed by value</I>
 594 you shouldn't use <TT>const</TT>.
 595 <P>Of course, it doesn't apply to functions such as
 596 <TT>void PrintMessage(const char *text)</TT> where <TT>const</TT> is mandatory.
 597   </OL>
 598 </UL>
 599
 600 <P>
 601
 602 <H3>wxWindows rules</H3>
 603 <UL>
 604   <P><LI>File location and naming conventions</LI><P>
 605   <OL>
 606     <P><LI><A NAME="file_locations"></LI><B>File locations</B><P>
 607 The wxWindows files for each supported platform have their own subdirectories
 608 in "include" and "src". So, for example, there is "src/msw", "include/gtk"
 609 etc. There are also two special subdirectories called "common" and
 610 "generic". The common subdirectory contains the files which are platform
 611 independent (wxObject, wxString, ...) and the generic one the generic
 612 implementations of GUI widgets, i.e. those which use only other wxWindows
 613 classes to implement them. For the platforms where the given functionality
 614 cannot be implemented natively, the generic implementation is used and the native
 615 one is used for the others. As I feel that it becomes a bit too confusing,
 616 here is an example: wxMessageBox function is implemented natively under
 617 Windows (where it just calls MessageBox API), but there is also a generic
 618 implementation which is used under, for example, GTK. A generic class should
 619 normally have a name that distinguishes it from any platform-specific implementation.
 620 A #define will allow wxGenericMessageDialog to be wxMessageDialog on some
 621 platforms, for example.
 622
 623 <P>This scheme applies not only for the .cpp files, but also for the headers.
 624 However, as the program using wxWindows should (ideally) not use any
 625 "<TT>&#35;ifdef &lt;platform&gt;</TT>" at all, the headers are always included with
 626 "<TT>&#35;include &lt;wx/msgdlg.h&gt;</TT>" (for example). This file, in turn, includes
 627 the right header for given platform. Any new headers should conform to this
 628 setup as well to allow including <TT>&lt;wx/foo.h&gt;</TT> on any platform.<P>
 629
 630 Note that wxWindows implementation files should use quotes when including wxWindows
 631 headers, not angled brackets. Applications should use angled brackets. There
 632 is a reason for it (can anyone remember what this is?).
 633
 634     <P><LI><A NAME="include_guards"></LI><B>Include guards</B><P>
 635 To minimize the compile time C++ programmers often use so called include
 636 guards: for example, in the header file foo.h you might have
 637
 638 <PRE>
 639 &#35;ifndef _FOO_H_
 640 &#35;define _FOO_H_
 641
 642 ... all header contents ...
 643
 644 &#35;endif
 645  //_FOO_H_
 646 </PRE>
 647
 648 In this way, the header will only be included once for the compilation
 649 of any .cpp (of course, it still will be included many times for the
 650 compilation of the whole project, so it has nothing to do with precompiled
 651 headers). wxWindows is no exception and also uses include guards which should use
 652 the above form, except for top-level headers which include files with identical
 653 names, in which case you should use _FOO_H_BASE_.
 654
 655     <P><LI><A NAME="pch"></LI><B>Precompiled headers</B><P>
 656 The precompiled headers greatly (we're speaking about orders of hundreds of
 657 percent here) reduce the compilation time. wxWindows uses them if the target
 658 compiler supports them (it knows about MS Visual C++, Borland C++ and g++).
 659 You should include all the headers included from <TT><wx/wx_prec.h></TT> only
 660 inside "<TT>&#35;if !USE_PRECOMP</TT>" to avoid unnecessary overhead in the case
 661 when the precompiled headers are used.<P>
 662
 663 The start of a cpp implementation file after the heading might look like this:<P>
 664
 665 <PRE>
 666 &#35;ifdef __GNUG__
 667 &#35;pragma implementation "bitmap.h"
 668 &#35;endif
 669
 670 // For compilers that support precompilation, includes "wx.h".
 671 &#35;include "wx/wxprec.h"
 672
 673 &#35;ifdef __BORLANDC__
 674 &#35;pragma hdrstop
 675 &#35;endif
 676
 677 &#35;ifndef WX_PRECOMP
 678 &#35;include &lt;stdio.h&gt;
 679 &#35;include "wx/setup.h"
 680 &#35;include "wx/list.h"
 681 &#35;include "wx/utils.h"
 682 &#35;include "wx/app.h"
 683 &#35;include "wx/palette.h"
 684 &#35;include "wx/bitmap.h"
 685 &#35;include "wx/icon.h"
 686 &#35;endif
 687
 688 &#35;include "wx/msw/private.h"
 689 &#35;include "assert.h"
 690 </PRE>
 691
 692
 693 <P>Any header file should containg the following lines:
 694 <PRE>
 695 &#35;ifdef __GNUG__
 696   &#35;pragma interface "foo.h"
 697 &#35;endif
 698 </PRE>
 699 and the corresponding .cpp file:
 700 <PRE>
 701 &#35;ifdef __GNUG__
 702   &#35;pragma  implementation "foo.h"
 703 &#35;endif
 704 </PRE> for g++ compilation.
 705   </OL>
 706
 707   <P><LI>File layout and indentation</LI><P>
 708   <OL>
 709     <P><LI><A NAME="wxwin_header"></LI><B>wxWindows standard header</B> <a href="header.txt">here</a>. The
 710 copyright holder is the original author. It is assumed the author does not assert copyright,
 711 under the terms of the wxWindows licence. This is a legal interpretation of the informal
 712 usage 'public domain' (the copyright holder does not assert the copyright).<P>
 713     <P><LI><A NAME="indentation"></LI><B>Indent your code with 4 spaces (no tabs!)</B>
 714     <P><LI><A NAME="class_decl"></LI><B>Order of parts in a class declarations</B><P>
 715   </OL>
 716
 717   <P><LI>More about naming conventions</LI><P>
 718   <OL>
 719     <P><LI><A NAME="wx_prefix"></LI><B>Use wx or WX prefix for all public symbols</B>.
 720 wx should be used for functions and classes, WX for macros.
 721     <P><LI><A NAME="wxdllexport"</LI><B>Use WXDLLEXPORT with all classes/functions in
 722                                 wxMSW/common code</B>
 723 The title says it all - every public (in the sense that it is not internal to
 724 the library) function or class should have WXDLLEXPORT macro in its
 725 declaration to allow compilation of wxWindows as shared library. For example:<P>
 726
 727 <pre>
 728 bool WXDLLEXPORT wxYield(void);
 729 class WXDLLEXPORT MyClass;  // (for forward declarations and real declarations)
 730 WXDLLEXPORT_DATA(extern wxApp*) wxTheApp;
 731 </pre>
 732
 733 The reason for the strange syntax for data is that some compilers use different
 734 keyword ordering for exporting data.
 735
 736 <P>There also several other places where you should take care of shared
 737 library case: all IMPLEMENT_xxx macros which are usually used in the
 738 corresponding .cpp files must be taken inside
 739 "<TT>&#35;if !USE_SHARED_LIBRARY</TT>" and in the <TT>&#35;if USE_SHARED_LIBRARY</TT>
 740 case you should put them inside <TT>common/cmndata.cpp</TT> file.
 741
 742     <P><LI><A NAME="set_get"></LI><B>Use Set/Get prefixes for accessors</B><P>
 743 There is a convention in wxWindows to prefix the accessors (i.e. any simple, in
 744 general, inline function which does nothing else except changing or returning
 745 the value of a member variable) with either <TT>Set</TT> or <TT>Get</TT>.
 746
 747     <P><LI><A NAME="constants"></LI><B>wxNAMING_CONSTANTS</B><P>
 748 The constants in wxWindows code should be defined using <TT>enum</TT> C++
 749 keyword (and not with <TT>#define</TT> or <TT>static const int</TT>). They
 750 should be declared in the global scope (and not inside class declaration) and
 751 their names should start with a <TT>wx</TT> prefix. Finally, the constants
 752 should be in all capital letters (except the first 2) to make it easier to
 753 distinguish them from the variables with underscores separating the words.
 754
 755 <P>For example, file-related constants should be declared like this:
 756 <pre>
 757 enum
 758 {
 759     wxFILEOPEN_READ,
 760     wxFILEOPEN_WRITE,
 761     wxFILEOPEN_READWRITE
 762 };
 763 </pre>
 764
 765   </OL>
 766
 767   <P><LI>Miscellaneous</LI><P>
 768   <OL>
 769     <P><LI><A NAME="forward_decl"></LI><B>Use forward declarations whenever possible</B><P>
 770 It's really a trivial piece of advice, but remember that using forward declarations
 771 instead of including the header of corresponding class is better because not
 772 only does it minimize the compile time, it also simplifies the dependencies
 773 between different source files.
 774 <P>On a related subject, in general, you should try not to include other
 775 headers from a header file.
 776
 777     <P><LI><A NAME="debug_macros"></LI><B>Use debugging macros</B><P>
 778 wxWindows provides the debugging macros <TT>wxASSERT, wxFAIL</TT> and
 779 <TT>wxCHECK_RET</TT> in <TT><wx/wx.h></TT> file. Please use them as often as
 780 you can - they will never do you any harm but can greatly simplify the bug
 781 tracking both for you and for others.
 782 <P>Also, please use <TT>wxFAIL_MSG("not implemented")</TT> instead of writing
 783 stubs for not (yet) implemented functions which silently return incorrect
 784 values - otherwise, a person using a not implemented function has no idea that
 785 it is, in fact, not implemented.
 786 <P>As all debugging macros only do something useful if the symbol
 787 <TT>__WXDEBUG__</TT> is defined, you should compile your programs in debug mode to profit
 788 from them.
 789   </OL>
 790 </UL>
 791
 792 <P>
 793
 794 <HR>
 795 Please send any comments to <A HREF=mailto:zeitlin@dptmaths.ens-cachan.fr>Vadim Zeitlin</A>.
 796
 797 </font>
 798
 799 </BODY>
 800 </HTML>