Can argc be zero on a POSIX system?

Question

Given the standard definition for the main program:

int main(int argc, char *argv[]) {
   ...
}

Under which circumstances can argc

Answer 1

To add to the other answers, there is nothing in C (POSIX or not) preventing main() from being called as a function within the program.

int main(int argc, int argv[]) {
    if (argc == 0) printf("Hey!\n");
    else main(0,NULL);

    return 0;
}