Projects/KDE on Windows/Porting Guidelines: Difference between revisions

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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.
{{Moved To Community|Windows/Imported From TechBase/{{#titleparts:{{PAGENAME}}||3}}}}
 
 
==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:
 
<syntaxhighlight lang="c">
  if (path[0]=='/')
</syntaxhighlight>
or:
 
<syntaxhighlight lang="cpp-qt">
  if (path.startsWith('/'))
</syntaxhighlight>
with:
 
<syntaxhighlight lang="cpp-qt">
  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
<syntaxhighlight lang="c">
  #ifdef Q_WS_X11
  ....
#endif
</syntaxhighlight>
for any C++ code that looks like X11-only.
 
Use
<syntaxhighlight lang="c">
  #ifdef Q_OS_UNIX
  ....
#endif
</syntaxhighlight>
for any C++ code that looks like UNIX-only, for example uses UNIX-specific OS features.
 
Use
<syntaxhighlight lang="c">
  #ifdef Q_WS_WIN
  ....
#endif
</syntaxhighlight>
for any C++ code that is MSWindows-only.
 
===C code===
Note that qglobal.h is C++-only, so instead use
<syntaxhighlight lang="c">
  #ifdef _WIN32
  ....
#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)====
<syntaxhighlight lang="cpp">
  #ifdef _MSC_VER
  ....//msvc code
#endif
</syntaxhighlight>
 
====MS Visual C++ - Qt code====
<syntaxhighlight lang="cpp">
  #ifdef Q_CC_MSVC
  ....//msvc code
#endif
</syntaxhighlight>
 
====Borland C++ - Qt-independent code (especially, C code)====
<syntaxhighlight lang="cpp">
  #ifdef __BORLANDC__
  ....//borland code
#endif
</syntaxhighlight>
 
====Borland C++ - Qt code====
<syntaxhighlight lang="cpp">
  #ifdef Q_CC_BOR
  ....//borland code
#endif
</syntaxhighlight>
 
===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===
* [http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclang/html/_predir_predefined_macros.asp| 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:
<syntaxhighlight lang="c">
#include <kdemacros.h>
</syntaxhighlight>
or
<syntaxhighlight lang="c">
#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 [http://lists.kde.org/?l=kde-core-devel&m=105154800130902&w=2|discussed] 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:
 
<syntaxhighlight lang="cpp">
class KDEFOO_EXPORT FooClass {
...
};
</syntaxhighlight>
 
'''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:
 
<syntaxhighlight lang="cpp">
#define KDE_NO_EXPORT __attribute__ ((visibility("hidden")))
#define KDE_EXPORT __attribute__ ((visibility("default")))
</syntaxhighlight>
 
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:
<syntaxhighlight lang="cpp">
  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)
</syntaxhighlight>
 
===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:
<syntaxhighlight lang="cpp">
namespace Foo {
KDEFOO_EXPORT int publicFunction();
}
</syntaxhighlight>
 
===What not to export?===
* methods inside classes (no matter static or not)
* inline functions
* template classes, e.g.:
 
<syntaxhighlight lang="cpp">
template <class T>
class KGenericFactoryBase
</syntaxhighlight>
 
 
 
===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:
 
<syntaxhighlight lang="cpp">
class KDEFOO_EXPORT KDE_DEPRECATED FooClass { //< - bad for moc!
...
};
</syntaxhighlight>
 
..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):
 
<syntaxhighlight lang="cpp">
# ifndef KABC_EXPORT_DEPRECATED
#  define KABC_EXPORT_DEPRECATED KDE_DEPRECATED KABC_EXPORT
# endif
</syntaxhighlight>
 
So, we have following example of deprecated class:
 
<syntaxhighlight lang="cpp">
class KABC_EXPORT_DEPRECATED FooClass { //<- ok for moc
...
};
</syntaxhighlight>
 
.. 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==
 
{{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:
<syntaxhighlight lang="cpp">
extern "C" {void *init_libname() { return new factory; } };
</syntaxhighlight>
...because the former way is more portable (contains proper export macro, which ensures visiblility of "init_libname" symbol).
 
Examples:
<syntaxhighlight lang="cpp">
K_EXPORT_COMPONENT_FACTORY( ktexteditor_insertfile,
    GenericFactory<InsertFilePlugin>( "ktexteditor_insertfile" ) )
K_EXPORT_COMPONENT_FACTORY( libkatepart, KateFactoryPublic )
</syntaxhighlight>
 
===More complex case===
 
Sometimes you need to declare a factory which defined as a template with multiple arguments, eg.:
 
<syntaxhighlight lang="cpp">
extern "C"
{
  void* init_resourcecalendarexchange()
  {
    return new KRES::PluginFactory<ResourceExchange,ResourceExchangeConfig>();
  }
}
</syntaxhighlight>
 
... but compiler complains about too many arguments passed to K_EXPORT_COMPONENT_FACTORY. To avoid this, you can use __typedef__:
 
<syntaxhighlight lang="bash">
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.
 
==Templates==
MSVC 6 templates support was heavily broker. Since then the situation has improved a lot. However some specific cases do exist and these are explained in this section.
 
===Template arguments need to be defined in header files===
This won't work with forward declaration:
<syntaxhighlight lang="cpp-qt">
class QColor;
#include <QList>
QList<QColor> foo; // error
</syntaxhighlight>
 
You need to include full QColor declaration too:
<syntaxhighlight lang="cpp-qt">
#include <QColor>
#include <QList>
QList<QColor> foo; // ok
</syntaxhighlight>
So this is different when compared to GCC.
 
===“non-class type as already been declared as a class type” errors===
Code like this breaks in MSVC 2008/2010 (works under GCC and standard says it should work):
<syntaxhighlight lang="cpp-qt">
template <typename T>
void foo(struct bar & b);
 
struct bar {};
int main() {}
</syntaxhighlight>
This causes ''“non-class type as already been declared as a class type”'' error. The example is quoted after this [http://stackoverflow.com/questions/5995774/forward-declared-type-and-non-class-type-as-already-been-declared-as-a-class-ty stackoverflow entry]. See also a [https://connect.microsoft.com/VisualStudio/feedback/details/668430/forward-declared-type-and-non-class-type-as-already-been-declared-as-a-class-type bug report] sent to MS, when the vendor rejects request for fixing this bug.
 
A fix exists under MSVC 2008/2010: "struct bar;" should be added before the template function declaration
<syntaxhighlight lang="cpp-qt">
struct bar {};
 
template <typename T>
void foo(struct bar & b);
 
int main() {}
</syntaxhighlight>
In practice, if our templated declaration is a class like QList<>, we have to add the ''struct bar {};'' declaration before #include <QList>.
<syntaxhighlight lang="cpp-qt">
struct bar {};
 
#include <QList>
QList<bar> myFunction();
 
int main() {}
</syntaxhighlight>
 
MSVC 2008/2010 changed its behaviour what can be perceived as broken, with regression compared to 2005.
 
==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. [[Development/CMake/Addons for KDE#Macros|More information on KDE4_ADD_APP_ICON() macro...]]

Latest revision as of 14:18, 11 March 2016

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