Question

We can write main function in several ways,

1. int main()
2. int main(int argc,char *argv[])
3. int main(int argc,char *argv[],char * environment)

How run-time CRT function knows which main should be called. Please notice here, I am not asking about Unicode supported or not.

Answer 1

The accepted answer is incorrect, there’s no special code in the CRT to recognize the kind of main() declaration.

It works because of the cdecl calling convention. Which specifies that arguments are pushed on the stack from right to left and that the caller cleans up the stack after the call. So the CRT simply passes all arguments to main() and pops them again when main() returns. The only thing you need to do is specify the arguments in the right order in your main() function declaration. The argc parameter has to be first, it is the one on the top of the stack. argv has to be second, etcetera. Omitting an argument makes no difference, as long as you omit all the ones that follow as well.

This is also why the printf() function can work, it has a variable number of arguments. With one argument in a known position, the first one.