Question

In this code:

int main(int a, int b)
{
    printf(" main(int, int) works \n\n");
    return 0;
}

the signature of main is main(int, int), and it compiles successfully. Why?

Answer 1

Because the C standard doesn’t prohibit non-standard signatures for main (see e.g. section 5.1.2 of the C99 standard).

However, you’ll find that if you compile under GCC with the -Wall flag,¹ it will complain:

test.c:4: warning: second argument of 'main' should be 'char **'

It assumes that you want to interact with a standard environment (i.e. process command-line parameters and return an exit status), in which case you must use int main(int, char **) or int main(void). If you use anything else, the contents of the arguments will be undefined.

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_{1. I really wish ideone.com would allow you to specify compiler flags!}