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.)

score 5 · Accepted Answer · answered Jan 12 '12 at 09:59

5

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

answered Jan 12 '12 at 09:59

celtschk

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1

I thought that would be included by `-Wall`, but obviously I was wrong. :-) – Peter T.B. Brett Jan 12 '12 at 11:46

score 2 · Answer 2 · answered Jan 12 '12 at 10:18

Note that gcc with -std=c99 -pedantic -Wall options doesn't issue any warning for the old style function declarations but C doesn't require the implementation to issue a diagnostic in presence of the old style function declarations.

C characterizes the use of old style function declaration as obsolescent since C89 but it it still valid C code (in C89/C99/C11).

Getting compilation warnings for non-prototype declarations

2 Answers2