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Chapter 5Target Platforms
By Felipe Monteiro de Carvalho
Lazarus programs can be compiled to run on three major computer
platforms:Windows, Linux/Unix, and MacOS X. That is fewer platforms
than the FreePascal compiler is able to target. The reason for this
is that appropriate compiler
capability is not the only condition that must be met before you
can create aLazarus program for a new platform.
The following three conditions have to be fulfilled before you
can install and use Lazaruson any platform:
A current Free Pascal compiler for the must be available. At
themoment these are available for Windows 32, Windows 64, Windows
CE, MacOS X,Linux, FreeBSD and OS/2 (and eComStation) and (to a
certain extent) for Solaris.
A current Free Pascal compiler for the must be available. At the
moment
these are available for x86, x86_64, PowerPC, PowerPC64 and
Arm(ARM4-instruction set only the THUMB instruction set is not
supported).
There must be a available for the operating system
platform.Currently fully supported are Windows, Windows CE and
MacOS X, and also theLinux/Unix widget-set Gtk versions 1 and 2,
and the platform-independent Qt 4(Unix, MacOS, Windows).
This third requirement is the reason it is not possible to
create OS/2 programs withLazarus. A Free Pascal compiler for
x86-OS/2 exists, but there is no support for theOS/2 presentation
manager and for eComStation. In theory it should be possible
toinstall Lazarus under XFree86/2 and create OS/2 programs for X.
Nobody has tried thisyet, but all the requirements can be met:
there is a compiler and there is a port of Gtkversion 2.
There are huge differences between the four basic platforms
Win32/64, WinCE, MacOSand Linux/FreeBSD/Solaris. For that reason it
is important if you want to createapplications to run on multiple
platforms (or if you intend to port software from oneplatform to
another) to get acquainted with the details of using Lazarus on
each of theseplatforms before making a start. That way you can
investigate beforehand what problemsyou might encounter, and so
make the right choices when designing software to run on
all the desired platforms without problems. With some experience
you can then developsoftware completely on one platform, and simply
recompile your program to make itavailable on additional
platforms.
target platform
target CPU
GUI library
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Chapter 5 Target Platforms
This chapter gives a general overview of this theme, explaining
the main features of thedifferent operating systems, and also shows
you how to make use of the native APIs ifnecessary (although you
should normally avoid doing this if you are trying to
createportable software).
At first sight it would seem very easy to make sure programs
developed with Lazarus willrun on all platforms. If you use only
libraries that exist on all target platforms, and if youuse only
calls to the Free Pascal RTL and FCL and to the Lazarus LCL your
programswill work on all supported platforms, in theory, without
change. because thereare still many operating system differences to
keep in mind. If everything is done in theright way the RTL, FCL
and LCL will hide or minimise these differences, but we may
alsohave to work around them (and if the need arises we may have to
correct code manually).
It gets more difficult if we need functionality that is not
provided by Lazarus's libraries.It that case we will be forced to
find another library that does offer such functionality onmultiple
platforms (hopefully on all of them), or we will have to work with
the low-levelAPIs of each operating system to implement a solution
for each platform ourselves.In these cases we will have to use
.When we do that, parts of the source code for the different
operating systems will needto be separated. Free Pascal offers the
sequence of commands
to facilitate this.
However, having to interlace source code for different operating
systems in large routinesin this way is not ideal. A cleaner
solution is to provide separate source files, each offeringa
solution for one of the platforms. A good way to handle this in
Free Pascal and Lazarusis to make use of the meta-command to
include these parts of thecode into the source. A common convention
is to create one subdirectory per platformand put all
platform-specific code in the appropriate subdirectory.Anything
between the conditional commands and will be used only if
thecondition given after is True. This applies to the include
statements too.We can include a file for just one operating system
with a one-line construction in the
code.
A more elegant way is to use macros in search paths. If we
include $(TargetOS) in thesearch path for include files, we can
simply use:
In theory
conditional compilation
$ifdef $endif $ifdef
$ ifdef condition . . . $else . . . $endif
$include filename.inc
{$ifdef Linux} {$include linux.inc} {$endif}{$ifdef Win32}
{$include win32.inc} {$endif} / / . . . etc
{$include unit1.inc}
.
In that case the include file for Win32 might be located in:
Win32/unit1.incwhile the include file for Linux could be found
in:In this way all Linux-specific files can be stored together in
one directory.Macros can also be used for unit search paths.
Linux/unit1.inc
.
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