Windows/Porting Guidelines

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< Windows
Revision as of 20:40, 11 January 2008 by Jstaniek (talk | contribs)

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 commited yet.
  • You can ask maintainer for proposals, what can be useful for porting.
  • You will need KDE cvs account for your work.
  • Download most current (HEAD) of the KDE libraries.

Absolute dirs checking

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

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

or: 

 if (path.startsWith('/'))

with: 

 if (!QDir::isRelativePath(path))

(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
 ....
 #endif

for any C++ code that looks like X11-only.

Use 

 #ifdef Q_OS_UNIX
 ....
 #endif

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

Use 

 #ifdef Q_WS_WIN
 ....
 #endif

for any C++ code that is MSWindows-only.

C code

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

 #ifdef _WINDOWS
 ....
 #endif

for any C code that is MSWindows-only (regardless to compiler type). In fact, you could use built-in _WIN32 but it's not defined on incoming 64bit MS Windows platform (_WIN64 is used there). So, there's a global rule for kdelibs/win32 defined globally in your build system (you don't need to include any file for this).

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.

Related links

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>

or 

#include <kdecore_export.h>

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:

  1. define KDE_NO_EXPORT __attribute__ ((visibility("hidden")))
  2. 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):

  1. ifndef KABC_EXPORT_DEPRECATED
  2. define KABC_EXPORT_DEPRECATED KDE_DEPRECATED KABC_EXPORT
  3. 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

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)

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

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