1
/////////////////////////////////////////////////////////////////////////////
3
// Purpose: Cross-platform development page of the Doxygen manual
4
// Author: wxWidgets team
5
// RCS-ID: $Id: devtips.h 66709 2011-01-19 10:46:31Z VZ $
6
// Licence: wxWindows licence
7
/////////////////////////////////////////////////////////////////////////////
11
@page page_multiplatform General Cross-Platform Development Tips
13
This chapter describes some tips related to cross-platform development.
15
@li @ref page_multiplatform_includefiles
16
@li @ref page_multiplatform_libraries
17
@li @ref page_multiplatform_configuration
18
@li @ref page_multiplatform_makefiles
19
@li @ref page_multiplatform_winresources
20
@li @ref page_multiplatform_allocatingobjects
21
@li @ref page_multiplatform_architecturedependency
22
@li @ref page_multiplatform_conditionalcompilation
23
@li @ref page_multiplatform_cpp
24
@li @ref page_multiplatform_filehandling
25
@li @ref page_multiplatform_reducingerr
26
@li @ref page_multiplatform_gui
27
@li @ref page_multiplatform_debug
33
@section page_multiplatform_includefiles Include Files
35
The main include file is @c "wx/wx.h"; this includes the most commonly used
38
To save on compilation time, include only those header files relevant to the
39
source file. If you are using @b precompiled headers, you should include the
40
following section before any other includes:
43
// For compilers that support precompilation, includes "wx.h".
44
#include <wx/wxprec.h>
51
// Include your minimal set of headers here, or wx.h
55
... now your other include files ...
58
The file @c "wx/wxprec.h" includes @c "wx/wx.h". Although this incantation may
59
seem quirky, it is in fact the end result of a lot of experimentation, and
60
several Windows compilers to use precompilation which is largely automatic for
61
compilers with necessary support. Currently it is used for Visual C++
62
(including embedded Visual C++), Borland C++, Open Watcom C++, Digital Mars C++
63
and newer versions of GCC. Some compilers might need extra work from the
64
application developer to set the build environment up as necessary for the
69
@section page_multiplatform_libraries Libraries
71
All ports of wxWidgets can create either a @b static library or a @b shared
74
When a program is linked against a @e static library, the machine code from the
75
object files for any external functions used by the program is copied from the
76
library into the final executable.
78
@e Shared libraries are handled with a more advanced form of linking, which
79
makes the executable file smaller. They use the extension @c ".so" (Shared
80
Object) under Linux and @c ".dll" (Dynamic Link Library) under Windows.
82
An executable file linked against a shared library contains only a small table
83
of the functions it requires, instead of the complete machine code from the
84
object files for the external functions. Before the executable file starts
85
running, the machine code for the external functions is copied into memory from
86
the shared library file on disk by the operating system - a process referred to
87
as @e dynamic linking.
89
Dynamic linking makes executable files smaller and saves disk space, because
90
one copy of a library can be shared between multiple programs. Most operating
91
systems also provide a virtual memory mechanism which allows one copy of a
92
shared library in physical memory to be used by all running programs, saving
93
memory as well as disk space.
95
Furthermore, shared libraries make it possible to update a library without
96
recompiling the programs which use it (provided the interface to the library
99
wxWidgets can also be built in @b multilib and @b monolithic variants. See the
100
@ref page_libs for more information on these.
104
@section page_multiplatform_configuration Configuration
106
When using project files and makefiles directly to build wxWidgets, options are
107
configurable in the file @c "wx/XXX/setup.h" where XXX is the required
108
platform (such as @c msw, @c motif, @c gtk, @c mac).
110
Some settings are a matter of taste, some help with platform-specific problems,
111
and others can be set to minimize the size of the library. Please see the
112
@c "setup.h" file and @c "install.txt" files for details on configuration.
114
When using the @c "configure" script to configure wxWidgets (on Unix and other
115
platforms where configure is available), the corresponding @c "setup.h" files
116
are generated automatically along with suitable makefiles.
118
When using the RPM packages (or DEB or other forms of @e binaries) for
119
installing wxWidgets on Linux, a correct @c "setup.h" is shipped in the package
120
and this must not be changed.
124
@section page_multiplatform_makefiles Makefiles
126
On Microsoft Windows, wxWidgets has a different set of makefiles for each
127
compiler, because each compiler's @c 'make' tool is slightly different. Popular
128
Windows compilers that we cater for, and the corresponding makefile extensions,
129
include: Microsoft Visual C++ (.vc), Borland C++ (.bcc), OpenWatcom C++ (.wat)
130
and MinGW/Cygwin (.gcc). Makefiles are provided for the wxWidgets library
131
itself, samples, demos, and utilities.
133
On Linux, Mac and OS/2, you use the @c 'configure' command to generate the
134
necessary makefiles. You should also use this method when building with
135
MinGW/Cygwin on Windows.
137
We also provide project files for some compilers, such as Microsoft VC++.
138
However, we recommend using makefiles to build the wxWidgets library itself,
139
because makefiles can be more powerful and less manual intervention is
142
On Windows using a compiler other than MinGW/Cygwin, you would build the
143
wxWidgets library from the @c "build/msw" directory which contains the relevant
146
On Windows using MinGW/Cygwin, and on Unix, MacOS X and OS/2, you invoke
147
'configure' (found in the top-level of the wxWidgets source hierarchy), from
148
within a suitable empty directory for containing makefiles, object files and
151
For details on using makefiles, configure, and project files, please see
152
@c "docs/xxx/install.txt" in your distribution, where @c "xxx" is the platform
153
of interest, such as @c msw, @c gtk, @c x11, @c mac.
155
All wxWidgets makefiles are generated using Bakefile <http://www.bakefile.org/>.
156
wxWidgets also provides (in the @c "build/bakefiles/wxpresets" folder) the
157
wxWidgets bakefile presets. These files allow you to create bakefiles for your
158
own wxWidgets-based applications very easily.
162
@section page_multiplatform_winresources Windows Resource Files
164
wxWidgets application compilation under MS Windows requires at least one extra
165
file: a resource file.
167
The least that must be defined in the Windows resource file (extension RC) is
168
the following statement:
171
#include "wx/msw/wx.rc"
174
which includes essential internal wxWidgets definitions. The resource script
175
may also contain references to icons, cursors, etc., for example:
181
The icon can then be referenced by name when creating a frame icon. See the
182
Microsoft Windows SDK documentation.
184
@note Include "wx.rc" @e after any ICON statements so programs that search your
185
executable for icons (such as the Program Manager) find your application
190
@section page_multiplatform_allocatingobjects Allocating and Deleting wxWidgets Objects
192
In general, classes derived from wxWindow must dynamically allocated with
193
@e new and deleted with @e delete. If you delete a window, all of its children
194
and descendants will be automatically deleted, so you don't need to delete
195
these descendants explicitly.
197
When deleting a frame or dialog, use @b Destroy rather than @b delete so that
198
the wxWidgets delayed deletion can take effect. This waits until idle time
199
(when all messages have been processed) to actually delete the window, to avoid
200
problems associated with the GUI sending events to deleted windows.
202
In general wxWindow-derived objects should always be allocated on the heap
203
as wxWidgets will destroy them itself. The only, but important, exception to
204
this rule are the modal dialogs, i.e. wxDialog objects which are shown using
205
wxDialog::ShowModal() method. They may be allocated on the stack and, indeed,
206
usually are local variables to ensure that they are destroyed on scope exit as
207
wxWidgets does not destroy them unlike with all the other windows. So while it
208
is still possible to allocate modal dialogs on the heap, you should still
209
destroy or delete them explicitly in this case instead of relying on wxWidgets
212
If you decide to allocate a C++ array of objects (such as wxBitmap) that may be
213
cleaned up by wxWidgets, make sure you delete the array explicitly before
214
wxWidgets has a chance to do so on exit, since calling @e delete on array
215
members will cause memory problems.
217
wxColour can be created statically: it is not automatically cleaned
218
up and is unlikely to be shared between other objects; it is lightweight
219
enough for copies to be made.
221
Beware of deleting objects such as a wxPen or wxBitmap if they are still in
222
use. Windows is particularly sensitive to this, so make sure you make calls
223
like wxDC::SetPen(wxNullPen) or wxDC::SelectObject(wxNullBitmap) before
224
deleting a drawing object that may be in use. Code that doesn't do this will
225
probably work fine on some platforms, and then fail under Windows.
229
@section page_multiplatform_architecturedependency Architecture Dependency
231
A problem which sometimes arises from writing multi-platform programs is that
232
the basic C types are not defined the same on all platforms. This holds true
233
for both the length in bits of the standard types (such as int and long) as
234
well as their byte order, which might be little endian (typically on Intel
235
computers) or big endian (typically on some Unix workstations). wxWidgets
236
defines types and macros that make it easy to write architecture independent
239
wxInt32, wxInt16, wxInt8, wxUint32, wxUint16 = wxWord, wxUint8 = wxByte
241
where wxInt32 stands for a 32-bit signed integer type etc. You can also check
242
which architecture the program is compiled on using the wxBYTE_ORDER define
243
which is either wxBIG_ENDIAN or wxLITTLE_ENDIAN (in the future maybe
244
wxPDP_ENDIAN as well).
246
The macros handling bit-swapping with respect to the applications endianness
247
are described in the @ref group_funcmacro_byteorder section.
251
@section page_multiplatform_conditionalcompilation Conditional Compilation
253
One of the purposes of wxWidgets is to reduce the need for conditional
254
compilation in source code, which can be messy and confusing to follow.
255
However, sometimes it is necessary to incorporate platform-specific features
256
(such as metafile use under MS Windows). The @ref page_wxusedef symbols listed
257
in the file @c setup.h may be used for this purpose, along with any
262
@section page_multiplatform_cpp C++ Issues
264
The following documents some miscellaneous C++ issues.
266
@subsection page_multiplatform_cpp_templates Templates
268
wxWidgets does not use templates (except for some advanced features that are
269
switched off by default) since it is a notoriously unportable feature.
271
@subsection page_multiplatform_cpp_rtti Runtime Type Information (RTTI)
273
wxWidgets does not use C++ run-time type information since wxWidgets provides
274
its own run-time type information system, implemented using macros.
276
@subsection page_multiplatform_cpp_precompiledheaders Precompiled Headers
278
Some compilers, such as Borland C++ and Microsoft C++, support precompiled
279
headers. This can save a great deal of compiling time. The recommended approach
280
is to precompile @c "wx.h", using this precompiled header for compiling both
281
wxWidgets itself and any wxWidgets applications. For Windows compilers, two
282
dummy source files are provided (one for normal applications and one for
283
creating DLLs) to allow initial creation of the precompiled header.
285
However, there are several downsides to using precompiled headers. One is that
286
to take advantage of the facility, you often need to include more header files
287
than would normally be the case. This means that changing a header file will
288
cause more recompilations (in the case of wxWidgets, everything needs to be
289
recompiled since everything includes @c "wx.h").
291
A related problem is that for compilers that don't have precompiled headers,
292
including a lot of header files slows down compilation considerably. For this
293
reason, you will find (in the common X and Windows parts of the library)
294
conditional compilation that under Unix, includes a minimal set of headers; and
295
when using Visual C++, includes @c "wx.h". This should help provide the optimal
296
compilation for each compiler, although it is biased towards the precompiled
297
headers facility available in Microsoft C++.
301
@section page_multiplatform_filehandling File Handling
303
When building an application which may be used under different environments,
304
one difficulty is coping with documents which may be moved to different
305
directories on other machines. Saving a file which has pointers to full
306
pathnames is going to be inherently unportable.
308
One approach is to store filenames on their own, with no directory information.
309
The application then searches into a list of standard paths (platform-specific)
310
through the use of wxStandardPaths.
312
Eventually you may want to use also the wxPathList class.
314
Nowadays the limitations of DOS 8+3 filenames doesn't apply anymore. Most
315
modern operating systems allow at least 255 characters in the filename; the
316
exact maximum length, as well as the characters allowed in the filenames, are
317
OS-specific so you should try to avoid extremely long (> 255 chars) filenames
318
and/or filenames with non-ANSI characters.
320
Another thing you need to keep in mind is that all Windows operating systems
321
are case-insensitive, while Unix operating systems (Linux, Mac, etc) are
324
Also, for text files, different OSes use different End Of Lines (EOL). Windows
325
uses CR+LF convention, Linux uses LF only, Mac CR only.
327
The wxTextFile, wxTextInputStream, wxTextOutputStream classes help to abstract
328
from these differences. Of course, there are also 3rd party utilities such as
329
@c dos2unix and @c unix2dos which do the EOL conversions.
331
See also the @ref group_funcmacro_file section of the reference manual for the
332
description of miscellaneous file handling functions.
336
@section page_multiplatform_reducingerr Reducing Programming Errors
338
@subsection page_multiplatform_reducingerr_useassert Use ASSERT
340
It is good practice to use ASSERT statements liberally, that check for
341
conditions that should or should not hold, and print out appropriate error
344
These can be compiled out of a non-debugging version of wxWidgets and your
345
application. Using ASSERT is an example of `defensive programming': it can
346
alert you to problems later on.
348
See wxASSERT() for more info.
350
@subsection page_multiplatform_reducingerr_usewxstring Use wxString in Preference to Character Arrays
352
Using wxString can be much safer and more convenient than using @c wxChar*.
354
You can reduce the possibility of memory leaks substantially, and it is much
355
more convenient to use the overloaded operators than functions such as
356
@c strcmp. wxString won't add a significant overhead to your program; the
357
overhead is compensated for by easier manipulation (which means less code).
359
The same goes for other data types: use classes wherever possible.
363
@section page_multiplatform_gui GUI Design
365
@li <b>Use Sizers:</b> Don't use absolute panel item positioning if you can
366
avoid it. Every platform's native controls have very different sizes.
367
Consider using the @ref overview_sizer instead.
368
@li <b>Use wxWidgets Resource Files:</b> Use @c XRC (wxWidgets resource files)
369
where possible, because they can be easily changed independently of source
370
code. See the @ref overview_xrc for more info.
374
@section page_multiplatform_debug Debugging
376
@subsection page_multiplatform_debug_positivethinking Positive Thinking
378
It is common to blow up the problem in one's imagination, so that it seems to
379
threaten weeks, months or even years of work. The problem you face may seem
380
insurmountable: but almost never is. Once you have been programming for some
381
time, you will be able to remember similar incidents that threw you into the
382
depths of despair. But remember, you always solved the problem, somehow!
384
Perseverance is often the key, even though a seemingly trivial problem can take
385
an apparently inordinate amount of time to solve. In the end, you will probably
386
wonder why you worried so much. That's not to say it isn't painful at the time.
387
Try not to worry -- there are many more important things in life.
389
@subsection page_multiplatform_debug_simplifyproblem Simplify the Problem
391
Reduce the code exhibiting the problem to the smallest program possible that
392
exhibits the problem. If it is not possible to reduce a large and complex
393
program to a very small program, then try to ensure your code doesn't hide the
394
problem (you may have attempted to minimize the problem in some way: but now
395
you want to expose it).
397
With luck, you can add a small amount of code that causes the program to go
398
from functioning to non-functioning state. This should give a clue to the
399
problem. In some cases though, such as memory leaks or wrong deallocation, this
400
can still give totally spurious results!
402
@subsection page_multiplatform_debug_usedebugger Use a Debugger
404
This sounds like facetious advice, but it is surprising how often people don't
405
use a debugger. Often it is an overhead to install or learn how to use a
406
debugger, but it really is essential for anything but the most trivial
409
@subsection page_multiplatform_debug_uselogging Use Logging Functions
411
There is a variety of logging functions that you can use in your program: see
412
@ref group_funcmacro_log.
414
Using tracing statements may be more convenient than using the debugger in some
415
circumstances (such as when your debugger doesn't support a lot of debugging
416
code, or you wish to print a bunch of variables).
418
@subsection page_multiplatform_debug_usedebuggingfacilities Use the wxWidgets Debugging Facilities
420
You can use wxDebugContext to check for memory leaks and corrupt memory: in
421
fact in debugging mode, wxWidgets will automatically check for memory leaks at
422
the end of the program if wxWidgets is suitably configured. Depending on the
423
operating system and compiler, more or less specific information about the
424
problem will be logged.
426
You should also use @ref group_funcmacro_debug as part of a "defensive
427
programming" strategy, scattering wxASSERT()s liberally to test for problems in
428
your code as early as possible. Forward thinking will save a surprising amount
429
of time in the long run.
431
See the @ref overview_debugging for further information.