Projects/KDE on Windows/Porting Guidelines

This document contains rules useful when you are porting a KDE library to win32. Most of these rules are also valid for porting external libraries code, like application's libraries and even application's private code.

Before you start

• Make sure (ask KDElibs/win32 maintainer) that the library you selected for porting is not ported, but just not committed yet.
• You can ask the maintainer for proposals, what can be useful for porting.
• You will need KDE svn account for your work.
• Download most current (HEAD) of the KDE libraries.

Absolute directory checking

Look for '/' and "/" and change every single code like:

 if (path[0]=='/')

</syntaxhighlight> or:

 if (path.startsWith('/'))

</syntaxhighlight> with:

 if (!QDir::isRelativePath(path))

</syntaxhighlight> (or "QDir::isRelativePath(path)" if there was used path[[0]!='/').

Ifdefs

C++ code

Macros for C++ code are defined in qglobal.h file. If you've got included at least one Qt header, you probably have qglobal.h included already, otherwise, include it explicity.

Use

 #ifdef Q_WS_X11
 ....

1. endif

</syntaxhighlight> for any C++ code that looks like X11-only.

Use

 #ifdef Q_OS_UNIX
 ....

1. endif

</syntaxhighlight> for any C++ code that looks like UNIX-only, for example uses UNIX-specific OS features.

Use

 #ifdef Q_WS_WIN
 ....

1. endif

</syntaxhighlight> for any C++ code that is MSWindows-only.

C code

Note that qglobal.h is C++-only, so instead use

 #ifdef _WIN32
 ....

1. endif

</syntaxhighlight>

for any C code that is MSWindows-only (regardless to compiler type).

Rare cases: How to check in Windows-only code which compiler is used?

MS Visual C++ - Qt-independent code (especially, C code)

  #ifdef _MSC_VER
  ....//msvc code
#endif

MS Visual C++ - Qt code

  #ifdef Q_CC_MSVC
  ....//msvc code
#endif

Borland C++ - Qt-independent code (especially, C code)

  #ifdef __BORLANDC__
  ....//borland code
#endif

Borland C++ - Qt code

  #ifdef Q_CC_BOR
  ....//borland code
#endif

General notes

In many places using #ifdef Q_OS_UNIX / #else / #endif is more readable than separate #ifdefs.

NOTE!!! if you must ifdef parts of the code, which contain complete features, please file a bug report against kde-windows target, component porting, in kde's bugzilla, so that those can be fixed later.

Related links

• msvc++ Predefined Macros

Header files

Common header file

Unless there is are any header file from kdelibs included in your header file, you need to add:

#include <kdemacros.h> 

</syntaxhighlight> or

#include <kdecore_export.h> 

</syntaxhighlight> at the beginning of your header file to have some necessary system-independent macros defined.

Export macros

For win32 world, symbols are "hidden by default" (not visible by default as e.g. on unix). This has already been [1] on the kde mailing list.

For every library's code (not for standalone code), you need to make symbols exported for win32. Do this by adding ***_EXPORT macro (win32 export macro) after "class" keyword within any public class (and structure) declaration. You may also decide to put this macro even for non-public class, if you think that the class could be used somewhere outside your library.

Example:

class KDEFOO_EXPORT FooClass {
...
};

Note: For kdelibs, ***_EXPORT macros for are defined in kdelibs_export_win.h file (in kdelibs/win/ directory). You can study this file to see how the macros are defined. This file is simply included by kdelibs_export.h, for win32 target.

Note2: Recently we're prepared to gcc's export capatibilities, probably in versions newer than 3.4, just like these in win32's msvc compiler. In kdemacros.h file (included by kdelibs_export.h) there are defines prepared for this functionality:

#define KDE_NO_EXPORT __attribute__ ((visibility("hidden")))
#define KDE_EXPORT __attribute__ ((visibility("default")))

For gcc <= 3.4, KDE_EXPORT and KDE_NO_EXPORT macros are just empty. Note that we're not using KDE_NO_EXPORT for non-public symbols: in the future probably it will be better to use command line switch to turn hidding by default (as win32 compiler has).

Note3: *_EXPORT macros depend on MAKE_{LIBRARYNAME}_LIB macro. In KDE4 buildsystem (cmake) the latter is defined automatically by reusing {LIBRARYNAME}, for example MAKE_KATEINTERFACES_LIB is constructed when KATEINTERFACES library is compiled. The logic behind it is implemented in kdelibs/cmake/modules/KDE4Macros.cmake:

   if (WIN32)
      # for shared libraries/plugins a -DMAKE_target_LIB is required
      string(TOUPPER ${_target_NAME} _symbol)
      set(_symbol "MAKE_${_symbol}_LIB")
      set_target_properties(${_target_NAME} PROPERTIES DEFINE_SYMBOL ${_symbol})
endif (WIN32)

Exporting global functions

Also add the same ***_EXPORT at the beginning of public functions' declaration and definition (just before function's type). This also includes functions defined within a namespace.

Example:

namespace Foo {
 KDEFOO_EXPORT int publicFunction();
}

What not to export?

• methods inside classes (no matter static or not)
• inline functions
• template classes, e.g.:

template <class T>
class KGenericFactoryBase

Visibility

There are classes or functions that are made "internal", by design. If you really decided anybody could neven need to link against these classes/functions, you don't need to add **_EXPORT macro for them.

Deprecated classes

Before porting KDElibs to win32, I realized that deprecated classes already use KDE_DEPRECATED macro. We're unable to add another macro like this:

class KDEFOO_EXPORT KDE_DEPRECATED FooClass { //< - bad for moc!
...
};

..because moc'ing will fail for sure. We've defined special macros like that in kdelibs_export.h file (fell free to add your own if needed):

# ifndef KABC_EXPORT_DEPRECATED
#  define KABC_EXPORT_DEPRECATED KDE_DEPRECATED KABC_EXPORT
# endif

So, we have following example of deprecated class:

class KABC_EXPORT_DEPRECATED FooClass { //<- ok for moc
...
};

.. which is ok for __moc__. Note that sometimes KDE_DEPRECATED is also used at the end of functions. You don't need to change it for win32 in any way.

Loadable KDE modules/plugins

noframe

 

TODO
This is deprecated section; we should use K_PLUGIN_FACTORY and K_EXPORT_PLUGIN macros

K_EXPORT_COMPONENT_FACTORY macro

Use K_EXPORT_COMPONENT_FACTORY( libname, factory ), defined in klibloader.h, instead of hardcoding:

 extern "C" {void *init_libname() { return new factory; } };

...because the former way is more portable (contains proper export macro, which ensures visiblility of "init_libname" symbol).

Examples:

K_EXPORT_COMPONENT_FACTORY( ktexteditor_insertfile,
    GenericFactory<InsertFilePlugin>( "ktexteditor_insertfile" ) ) 
K_EXPORT_COMPONENT_FACTORY( libkatepart, KateFactoryPublic )

More complex case

Sometimes you need to declare a factory which defined as a template with multiple arguments, eg.:

extern "C"
{
  void* init_resourcecalendarexchange()
  {
    return new KRES::PluginFactory<ResourceExchange,ResourceExchangeConfig>();
  }
}

... but compiler complains about too many arguments passed to K_EXPORT_COMPONENT_FACTORY. To avoid this, you can use __typedef__:

typedef KRES::PluginFactory<ResourceExchange,ResourceExchangeConfig> MyFactory; K_EXPORT_COMPONENT_FACTORY(resourcecalendarexchange, MyFactory) </syntaxhighlight>

The same trick can be used if the constructor of the factory takes multiple arguments.

Application icons

Windows keeps icon data within .exe binaries. For KDE applications use CMake's KDE4_ADD_APP_ICON(appsources pattern) macro in automatically assign to add .png images for .exe files. More information on KDE4_ADD_APP_ICON() macro...