What is the point of defining a calling convention?

Question

For example:

int WINAPI WinMain ( HINSTANCE instance, HINSTANCE prev_instance, PSTR cmd_line, int cmd_show )

WINAPI is a a define that looks li

Answer 1

This was originally done during the switchover from 16-bit to 32-bit code. In the 16-bit version of <windows.h> it was:

#define WINAPI __pascal

WINAPI let you compile for either without modifying the source code. Of course, 16-bit Windows is no longer a factor (at least for most people), but it's still not worth changing all the source code to use __stdcall directly (especially since it could change again someday).

Answer 2

Because the WINAPI calling convention is not guaranteed to be __stdcall. Code that uses WINAPI will still be correct even when it isn't.

You can write the function as in your latter example, and it'd work fine - it's just not good practice and would not be portable to a platform where the calling convention is something else.

Answer 3

Also, back in the day, some Windows libraries used Pascal calling convention and other libraries used C convention. A preprocessor define helped gloss over that.

Answer 4

You can just write __stdcall in its place, but don't. They've seen fit to #define WINAPI to __stdcall to make that opaque, which is just good programming practice.

Answer 5

Because WINAPI is a macro (well a #define anyway) it can be "pre-processed" to mean something else or even nothing at all.

That means you can write more portable code, as you can put in WINAPI when it is required by Win32 to mean __stdcall but, or if it is required in another environment to mean something else or nothing.