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\chapter{Multi-platform development with wxWidgets}\label{multiplat}
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This chapter describes the practical details of using wxWidgets. Please
see the file install.txt for up-to-date installation instructions, and
changes.txt for differences between versions.

\section{Include files}\label{includefiles}

The main include file is {\tt "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 precompiled headers, you should include
the following section before any other includes:

\begin{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 ...
\end{verbatim}

The file {\tt "wx/wxprec.h"} includes {\tt "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{Libraries}\label{libraries}

Most ports of wxWidgets can create either a static library or a shared
library. wxWidgets can also be built in multilib and monolithic variants.
See the \helpref{libraries list}{librarieslist} for more
information on these.

\section{Configuration}\label{configuration}

When using project files and makefiles directly to build wxWidgets,
options are configurable in the file
\rtfsp{\tt "wx/XXX/setup.h"} where XXX is the required platform (such as msw, motif, gtk, 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 setup.h file
and {\tt install.txt} files for details on configuration.

When using the 'configure' script to configure wxWidgets (on Unix and other platforms where
configure is available), the corresponding setup.h files are generated automatically
along with suitable makefiles. When using the RPM packages
for installing wxWidgets on Linux, a correct setup.h is shipped in the package and
this must not be changed.

\section{Makefiles}\label{makefiles}

On Microsoft Windows, wxWidgets has a different set of makefiles for each
compiler, because each compiler's '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 '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 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 docs/xxx/install.txt in your distribution, where
xxx is the platform of interest, such as msw, gtk, x11, mac.

\section{Windows-specific files}\label{windowsfiles}

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

\subsection{Resource file}\label{resources}

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

\begin{verbatim}
#include "wx/msw/wx.rc"
\end{verbatim}

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

\begin{verbatim}
wxicon icon wx.ico
\end{verbatim}

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

\normalbox{Note: include wx.rc {\it after} any ICON statements
so programs that search your executable for icons (such
as the Program Manager) find your application icon first.}

\section{Allocating and deleting wxWidgets objects}\label{allocatingobjects}

In general, classes derived from wxWindow must dynamically allocated
with {\it new} and deleted with {\it 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 {\bf Destroy} rather than {\bf 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 {\it 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{Architecture dependency}\label{architecturedependency}

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 \helpref{Byte order macros}{byteordermacros} section.

\section{Conditional compilation}\label{conditionalcompilation}

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 symbols
listed in the file {\tt symbols.txt} may be used for this purpose,
along with any user-supplied ones.

\section{C++ issues}\label{cpp}

The following documents some miscellaneous C++ issues.

\subsection{Templates}\label{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{RTTI}\label{rtti}

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

\subsection{Type of NULL}\label{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

{\small
\begin{verbatim}
  wxWindow *my_window = (wxWindow*) NULL;
\end{verbatim}
}%

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

\subsection{Precompiled headers}\label{precompiledheaders}

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 {\tt "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 {\tt "wx.h"}!)

A related problem is that for compilers that don't have precompiled
headers, including a lot of header files slows down compilation