Getting compilation warnings for non-prototype declarations

Question

In C, function declarations can be prototype or non-prototype declarations. For example, consider the following minimal program:

int foo (); /* non-prototype declaration */

int bar (void); /* prototype declaration */

int main (int argc, char **argv)
{
  return 0;
}

Although in C99 non-prototype declarations are obsolete, I cannot get GCC to complain about them. For example, compiling the above program with GCC and all errors enabled just succeeds:

$ gcc -std=c99 -pedantic -Werror -Wall test.c
$

Is there any way to persuade GCC to emit warnings for function declarations that aren't prototypes?

(Question inspired by an answer by Keith Thompson.)

Answer 1

I think the option you are looking for is -Wstrict-prototypes