Can argc be zero on a POSIX system?
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;
}
Yes, it is possible. If you call your program as follows:
execl("./myprog", NULL, (char *)NULL);
Or alternately:
char *args[] = { NULL };
execv("./myprog", args);
Then in "myprog", argc
will be 0.
The standard also specifically allows for a 0 argc
as noted in section 5.1.2.2.1 regarding program startup in a hosted environment:
1 The function called at program startup is named
main
. The implementation declares no prototype for this function. It shall be defined with a return type ofint
and with no parameters:int main(void) { /* ... */ }
or with two parameters (referred to here as
argc
andargv
, though any names may be used, as they are local to the function in which they are declared):int main(int argc, char *argv[]) { /* ... */ }
or equivalent; or in some other implementation-defined manner.
2 If they are declared, the parameters to the
main
function shall obey the following constraints:
- The value of
argc
shall be nonnegative.argv[argc]
shall be a null pointer....
Note also that this means that if argc
is 0 then argv[0]
is guaranteed to be NULL. How printf
treats a NULL pointer when used as the argument to a %s
specifier is not spelled out in the standard however. Many implementations will output "(null)" in this case but it's not guaranteed.