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 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).