Thread: WINAPI, WINUSERAPI, and calling conventions...what the heck are these?!

Hi all--

I some programming in college using mostly C++ (and some Java) and we learned stuff like quick sorts, hash tables, red-black trees etc. The extent of input/output was cout << "Hello, World!"

I wanted to learn how to program windows and I searched the internet and everyone said "GET PETZOLD!" So I bought "programming windows 5th addition" (I think it's going out of print...should I be worried ??)

Anyways Petzold said I needed to be familiar with C programming...since I knew printf() and malloc() existed but had no idea how to use them, I got the K&R book and went through it.

NOW, I'm into chapter one of petzold (finally) and the hello world function begins with...

Code:

int WINAPI WinMain(HINSTANCE hInstance...){...}

which seemed very odd because nowhere in my c++ or c from k&r did functions ever have more than a return type followed by the function name and parameters in their declaration/definition.

Petzold just says it's a "calling convention" and determines how a function is to be placed on the stack. Expanding WINAPI to __stdcall. Okay...but then LATER in Chapter 2 he defines the true message box with the following:

Code:

WINUSERAPI int WINAPI MessageBoxA(HWND hWnd...){...}

Now this function has 2 calling conventions (WINAPI and WINUSERAPI)? How many can a function have? what are these exactly? does anyone know of a place somewhere that has a beginner's tutorial for these calling conventions? perusing the index...I cannot find any more information on either of these.

Any help would be appreciated!
Thanks!

You can ignore the WINUSERAPI. It is ultimately defined (on some compilers) to declspec(dllimport), which is a compiler specific instruction that can give a slight performance boost to DLL functions. When calling a function, you can also ignore the calling convention. The only time you need to remember a calling convention is when you declare a callback function (such as WinMain). In this case, Win32 functions expect the callback function to use the WINAPI (or __stdcall) calling convention. The default calling convention is __cdecl. Even if you forget, your compiler will probably give you a warning. You can find a technical overview of __stdcall and __cdecl here.

Thanks anonytmouse!

those links were interesting. It was also nice to know I can move on with learning such great tasks as opening a window or outputting a character without feeling totally lost =)