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[wxWidgets.git] / docs / doxygen / mainpages / devtips.h

/////////////////////////////////////////////////////////////////////////////
// Name:        devtips.h
// Purpose:     Cross-platform development page of the Doxygen manual
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////


/**

@page page_multiplatform Multi-platform development

This chapter describes some tips related to multi-platform development.

@li @ref page_multiplatform_includefiles
@li @ref page_multiplatform_libraries
@li @ref page_multiplatform_configuration
@li @ref page_multiplatform_makefiles
@li @ref page_multiplatform_winresources
@li @ref page_multiplatform_allocatingobjects
@li @ref page_multiplatform_architecturedependency
@li @ref page_multiplatform_conditionalcompilation
@li @ref page_multiplatform_cpp
@li @ref page_multiplatform_filehandling
@li @ref page_multiplatform_reducingerr
@li @ref page_multiplatform_gui
@li @ref page_multiplatform_debug

<hr>


@section page_multiplatform_includefiles Include files

The main include file is @c "wx/wx.h"; this includes the most commonly
used modules of wxWidgets.

To save on compilation time, include only those header files relevant to the
source file. If you are using @b precompiled headers, you should include
the following section before any other includes:

@verbatim
// For compilers that support precompilation, includes "wx.h".
#include <wx/wxprec.h>

#ifdef __BORLANDC__
#pragma hdrstop
#endif

#ifndef WX_PRECOMP
// Include your minimal set of headers here, or wx.h
#include <wx/wx.h>
#endif

... now your other include files ...
@endverbatim

The file @c "wx/wxprec.h" includes @c "wx/wx.h". Although this incantation
may seem quirky, it is in fact the end result of a lot of experimentation,
and several Windows compilers to use precompilation which is largely automatic for
compilers with necessary support. Currently it is used for Visual C++ (including
embedded Visual C++), Borland C++, Open Watcom C++, Digital Mars C++
and newer versions of GCC.
Some compilers might need extra work from the application developer to set the
build environment up as necessary for the support.



@section page_multiplatform_libraries Libraries

All ports of wxWidgets can create either a @b static library or a @b shared library.

When a program is linked against a @e static library, the machine code from the object 
files for any external functions used by the program is copied from the library into 
the final executable.

@e Shared libraries are handled with a more advanced form of linking, which makes the 
executable file smaller. They use the extension @c \91.so\92 (Shared Object) under Linux 
and @c '.dll' (Dynamic Link Library) under Windows.

An executable file linked against a shared library contains only a small table of the 
functions it requires, instead of the complete machine code from the object files for 
the external functions. 
Before the executable file starts running, the machine code for the external functions 
is copied into memory from the shared library file on disk by the operating 
system - a process referred to as @e dynamic linking.

Dynamic linking makes executable files smaller and saves disk space, because one copy 
of a library can be shared between multiple programs. 
Most operating systems also provide a virtual memory mechanism which allows one copy 
of a shared library in physical memory to be used by all running programs, saving 
memory as well as disk space.

Furthermore, shared libraries make it possible to update a library without recompiling 
the programs which use it (provided the interface to the library does not change).  

wxWidgets can also be built in @b multilib and @b monolithic variants.
See the @ref page_libs for more information on these.



@section page_multiplatform_configuration Configuration

When using project files and makefiles directly to build wxWidgets,
options are configurable in the file
@c "wx/XXX/setup.h" where XXX is the required platform (such as @c msw, @c motif, 
@c gtk, @c mac). 

Some settings are a matter of taste, some help with platform-specific problems, and
others can be set to minimize the size of the library. Please see the @c setup.h file
and @c install.txt files for details on configuration.

When using the @c 'configure' script to configure wxWidgets (on Unix and other platforms
where configure is available), the corresponding @c setup.h files are generated automatically
along with suitable makefiles. 

When using the RPM packages (or DEB or other forms of @e binaries) for installing 
wxWidgets on Linux, a correct @c setup.h is shipped in the package and
this must not be changed.



@section page_multiplatform_makefiles Makefiles

On Microsoft Windows, wxWidgets has a different set of makefiles for each
compiler, because each compiler's @c 'make' tool is slightly different.
Popular Windows compilers that we cater for, and the corresponding makefile
extensions, include: Microsoft Visual C++ (.vc), Borland C++ (.bcc),
OpenWatcom C++ (.wat) and MinGW/Cygwin (.gcc). Makefiles are provided
for the wxWidgets library itself, samples, demos, and utilities.

On Linux, Mac and OS/2, you use the @c 'configure' command to generate the 
necessary makefiles. You should also use this method when building with 
MinGW/Cygwin on Windows.

We also provide project files for some compilers, such as Microsoft VC++. 
However, we recommend using makefiles to build the wxWidgets library itself, 
because makefiles can be more powerful and less manual intervention is required.

On Windows using a compiler other than MinGW/Cygwin, you would build the wxWidgets 
library from the @c build/msw directory which contains the relevant makefiles.

On Windows using MinGW/Cygwin, and on Unix, MacOS X and OS/2, you invoke
'configure' (found in the top-level of the wxWidgets source hierarchy),
from within a suitable empty directory for containing makefiles, object 
files and libraries.

For details on using makefiles, configure, and project files,
please see @c docs/xxx/install.txt in your distribution, where
@c xxx is the platform of interest, such as @c msw, @c gtk, @c x11, @c mac.

All wxWidgets makefiles are generated using @link http://www.bakefile.org Bakefile @endlink.
wxWidgets also provides (in the @c build/bakefiles/wxpresets) the
<b>wxWidgets bakefile presets</b>: these files allow you to create bakefiles for
your own wxWidgets-based applications very easily.


@section page_multiplatform_winresources Windows Resource files

wxWidgets application compilation under MS Windows requires at least one
extra file: a resource file.

The least that must be defined in the Windows resource file (extension RC)
is the following statement:

@verbatim
#include "wx/msw/wx.rc"
@endverbatim

which includes essential internal wxWidgets definitions.  The resource script
may also contain references to icons, cursors, etc., for example:

@verbatim
wxicon icon wx.ico
@endverbatim

The icon can then be referenced by name when creating a frame icon. See
the MS Windows SDK documentation.

@note include wx.rc @e after any ICON statements
    so programs that search your executable for icons (such
    as the Program Manager) find your application icon first.



@section page_multiplatform_allocatingobjects Allocating and deleting wxWidgets objects

In general, classes derived from wxWindow must dynamically allocated
with @e new and deleted with @e delete. If you delete a window,
all of its children and descendants will be automatically deleted,
so you don't need to delete these descendants explicitly.

When deleting a frame or dialog, use @b Destroy rather than @b delete so
that the wxWidgets delayed deletion can take effect. This waits until idle time
(when all messages have been processed) to actually delete the window, to avoid
problems associated with the GUI sending events to deleted windows.

Don't create a window on the stack, because this will interfere
with delayed deletion.

If you decide to allocate a C++ array of objects (such as wxBitmap) that may
be cleaned up by wxWidgets, make sure you delete the array explicitly
before wxWidgets has a chance to do so on exit, since calling @e delete on
array members will cause memory problems.

wxColour can be created statically: it is not automatically cleaned
up and is unlikely to be shared between other objects; it is lightweight
enough for copies to be made.

Beware of deleting objects such as a wxPen or wxBitmap if they are still in use.
Windows is particularly sensitive to this: so make sure you
make calls like wxDC::SetPen(wxNullPen) or wxDC::SelectObject(wxNullBitmap) before deleting
a drawing object that may be in use. Code that doesn't do this will probably work
fine on some platforms, and then fail under Windows.



@section page_multiplatform_architecturedependency Architecture dependency

A problem which sometimes arises from writing multi-platform programs is that
the basic C types are not defined the same on all platforms. This holds true
for both the length in bits of the standard types (such as int and long) as
well as their byte order, which might be little endian (typically
on Intel computers) or big endian (typically on some Unix workstations). wxWidgets
defines types and macros that make it easy to write architecture independent
code. The types are:

wxInt32, wxInt16, wxInt8, wxUint32, wxUint16 = wxWord, wxUint8 = wxByte

where wxInt32 stands for a 32-bit signed integer type etc. You can also check
which architecture the program is compiled on using the wxBYTE_ORDER define
which is either wxBIG_ENDIAN or wxLITTLE_ENDIAN (in the future maybe wxPDP_ENDIAN
as well).

The macros handling bit-swapping with respect to the applications endianness
are described in the @ref group_funcmacro_byteorder section.



@section page_multiplatform_conditionalcompilation Conditional compilation

One of the purposes of wxWidgets is to reduce the need for conditional
compilation in source code, which can be messy and confusing to follow.
However, sometimes it is necessary to incorporate platform-specific
features (such as metafile use under MS Windows). The @ref page_wxusedef
symbols listed in the file @c setup.h may be used for this purpose,
along with any user-supplied ones.



@section page_multiplatform_cpp C++ issues

The following documents some miscellaneous C++ issues.

@subsection page_multiplatform_cpp_templates Templates

wxWidgets does not use templates (except for some advanced features that
are switched off by default) since it is a notoriously unportable feature.

@subsection page_multiplatform_cpp_rtti RTTI

wxWidgets does not use C++ run-time type information since wxWidgets provides
its own run-time type information system, implemented using macros.

@subsection page_multiplatform_cpp_null Type of NULL

Some compilers (e.g. the native IRIX cc) define NULL to be 0L so that
no conversion to pointers is allowed. Because of that, all these
occurrences of NULL in the GTK+ port use an explicit conversion such
as

@code
wxWindow *my_window = (wxWindow*) NULL;
@endcode

It is recommended to adhere to this in all code using wxWidgets as
this make the code (a bit) more portable.

@subsection page_multiplatform_cpp_precompiledheaders Precompiled headers

Some compilers, such as Borland C++ and Microsoft C++, support
precompiled headers. This can save a great deal of compiling time. The
recommended approach is to precompile @c "wx.h", using this
precompiled header for compiling both wxWidgets itself and any
wxWidgets applications. For Windows compilers, two dummy source files
are provided (one for normal applications and one for creating DLLs)
to allow initial creation of the precompiled header.

However, there are several downsides to using precompiled headers. One
is that to take advantage of the facility, you often need to include
more header files than would normally be the case. This means that
changing a header file will cause more recompilations (in the case of
wxWidgets, everything needs to be recompiled since everything includes @c "wx.h" !)

A related problem is that for compilers that don't have precompiled
headers, including a lot of header files slows down compilation
considerably. For this reason, you will find (in the common
X and Windows parts of the library) conditional
compilation that under Unix, includes a minimal set of headers;
and when using Visual C++, includes @c wx.h. This should help provide
the optimal compilation for each compiler, although it is
biased towards the precompiled headers facility available
in Microsoft C++.



@section page_multiplatform_filehandling File handling

When building an application which may be used under different
environments, one difficulty is coping with documents which may be
moved to different directories on other machines. Saving a file which
has pointers to full pathnames is going to be inherently unportable.

One approach is to store filenames on their own, with no directory
information. The application then searches into a list of standard
paths (platform-specific) through the use of wxStandardPaths.

Eventually you may want to use also the wxPathList class.

Nowadays the limitations of DOS 8+3 filenames doesn't apply anymore.
Most modern operating systems allow at least 255 characters in the filename;
the exact maximum length, as well as the characters allowed in the filenames,
are OS-specific so you should try to avoid extremely long (> 255 chars) filenames
and/or filenames with non-ANSI characters.

Another thing you need to keep in mind is that all Windows operating systems
are case-insensitive, while Unix operating systems (Linux, Mac, etc) are
case-sensitive.

Also, for text files, different OSes use different End Of Lines (EOL).
Windows uses CR+LF convention, Linux uses LF only, Mac CR only.

The wxTextFile, wxTextInputStream, wxTextOutputStream classes help to abstract
from these differences.
Of course, there are also 3rd party utilities such as @c dos2unix and @c unix2dos
which do the EOL conversions.

See also the @ref group_funcmacro_file section of the reference
manual for the description of miscellaneous file handling functions.


@section page_multiplatform_reducingerr Reducing programming errors

@subsection page_multiplatform_reducingerr_useassert Use ASSERT

It is good practice to use ASSERT statements liberally, that check for conditions
that should or should not hold, and print out appropriate error messages.

These can be compiled out of a non-debugging version of wxWidgets
and your application. Using ASSERT is an example of `defensive programming':
it can alert you to problems later on.

See ::wxASSERT for more info.

@subsection page_multiplatform_reducingerr_usewxstring Use wxString in preference to character arrays

Using wxString can be much safer and more convenient than using @c wxChar*.

You can reduce the possibility of memory leaks substantially, and it is much more
convenient to use the overloaded operators than functions such as @c strcmp.
wxString won't add a significant overhead to your program; the overhead is compensated
for by easier manipulation (which means less code).

The same goes for other data types: use classes wherever possible.



@section page_multiplatform_gui GUI design

@subsection page_multiplatform_gui_usesizers Use sizers

Don't use absolute panel item positioning if you can avoid it. Different GUIs have
very differently sized panel items. Consider using the @ref overview_sizer instead.

@subsection page_multiplatform_gui_useresources Use wxWidgets resource files

Use @c XRC (wxWidgets resource files) where possible, because they can be easily changed
independently of source code. See the @ref overview_xrc for more info.



@section page_multiplatform_debug Debugging

@subsection page_multiplatform_debug_positivethinking Positive thinking

It is common to blow up the problem in one's imagination, so that it seems to threaten
weeks, months or even years of work. The problem you face may seem insurmountable:
but almost never is. Once you have been programming for some time, you will be able
to remember similar incidents that threw you into the depths of despair. But
remember, you always solved the problem, somehow!

Perseverance is often the key, even though a seemingly trivial problem
can take an apparently inordinate amount of time to solve. In the end,
you will probably wonder why you worried so much. That's not to say it
isn't painful at the time. Try not to worry -- there are many more important
things in life.

@subsection page_multiplatform_debug_simplifyproblem Simplify the problem

Reduce the code exhibiting the problem to the smallest program possible
that exhibits the problem. If it is not possible to reduce a large and
complex program to a very small program, then try to ensure your code
doesn't hide the problem (you may have attempted to minimize the problem
in some way: but now you want to expose it).

With luck, you can add a small amount of code that causes the program
to go from functioning to non-functioning state. This should give a clue
to the problem. In some cases though, such as memory leaks or wrong
deallocation, this can still give totally spurious results!

@subsection page_multiplatform_debug_usedebugger Use a debugger

This sounds like facetious advice, but it is surprising how often people
don't use a debugger. Often it is an overhead to install or learn how to
use a debugger, but it really is essential for anything but the most
trivial programs.

@subsection page_multiplatform_debug_uselogging Use logging functions

There is a variety of logging functions that you can use in your program:
see @ref group_funcmacro_log.

Using tracing statements may be more convenient than using the debugger
in some circumstances (such as when your debugger doesn't support a lot
of debugging code, or you wish to print a bunch of variables).

@subsection page_multiplatform_debug_usedebuggingfacilities Use the wxWidgets debugging facilities

You can use wxDebugContext to check for
memory leaks and corrupt memory: in fact in debugging mode, wxWidgets will
automatically check for memory leaks at the end of the program if wxWidgets is suitably
configured. Depending on the operating system and compiler, more or less
specific information about the problem will be logged.

You should also use @ref group_funcmacro_debugging as part of a `defensive programming' strategy,
scattering wxASSERTs liberally to test for problems in your code as early as possible.
Forward thinking will save a surprising amount of time in the long run.

See the @ref overview_debugging for further information.


*/