Building on Windows creates __stdcall-convention static lib/dll regardless of compiler settings

[trollcop]

The culprit is here:
https://github.com/uclouvain/openjpeg/blob/master/src/lib/openjp2/openjpeg.h#L94

I don't know what is default calling convention on Lunix, but Cmake-GUI-generated Visual Studio project files are set to __cdecl. As a result of using OPJ_CALLCONV, all the exported functions end up __stdcall (something like func_name@2 when exported in DLL) and thus cannot be linked to from any __cdecl code.

Anyway, since I have no idea how this affects non-Windows builds, I'm just going to leave this out there. The fix was obviously to simply #define OPJ_CALLCONV to be a blank - remove __stdcall.

I'm also not sure the logic in #if defined(OPJ_STATIC) || !defined(_WIN32) is correct?
Anyway, I've managed to build static win32 libs for my project and they work OK.

[stweil]

Why should it not be possible to call a __stdcall function from __cdecl code? AFAIK __stdcall is commonly used for exported functions of Windows DLLs, and of course they can be called (otherwise it would be impossible to use a DLL) - you only need the correct declaration, then the compiler knows how to handle mixtures of different calling conventions. There is nothing wrong in using __stdcall for openjpeg, too.

Non-Windows targets are not affected at all.

[trollcop]

I don't know why it makes a difference, but my project (which uses openjpeg) and openjpeg project itself were both set to __cdecl in compiler properties.

But, I think, what happens is __stdcall - functions without .def file results in exported names being slightly mangled (like I said, _func_name@2 instead of just _func_name) in dll/lib exports. So the resulting .lib and/or .lib+dll cannot be linked by a __cdecl project. I can't think of any reason to mix calling conventions inside same library, and since this doesn't affect anything except windows, maybe just blanking OPJ_CALLCONV for all targets, and then Windows people can change convention from the Visual Studio project (if they really require it at all).

[mayeut]

As @stweil said, there's nothing wrong with using __stdcall. The only issue I can see is the opposite problem: someones changes the default compiler setting (let's say __stdcall) in their project & defines OPJ_STATIC to link with a static library that was built with default settings.
So if I had to do anything, it would be to force a calling convention even for static library.