Stupid GCC

[ewx]

$ cat t.c
#include <stdio.h>
int main(void) { return printf(""); }
$ gcc -Wall -c t.c
t.c: In function ‘main’:
t.c:2: warning: zero-length printf format string
$ gcc -Wall -Wno-format-zero-length -c t.c
$ gcc --version
gcc (Debian 4.3.2-1.1) 4.3.2
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Can anyone offer a plausible reason why:

• -Wformat-zero-length is on by default (i.e. implied by -Wformat and thus by -Wall)?
• Why it exists at all?

FTAOD, empty format strings are perfectly legitimate (and the GCC Manual knows this).

Comments

[simont]

The obvious case is when your format strings are generated at compile time by a system of cpp macros, and some of them come out empty.

(I've often thought that a lot of compiler warnings need a special case "unless it was generated by a macro", because the sorts of things that indicate a probable user error when they appear in handwritten code are often very similar to the sorts of things that are perfectly sensible preprocessor output.)

[ewx.livejournal.com]

An "unless unreachable" clause in particular ought to be a no-brainer, and would have saved at least two false positives that I can remember.

[simont]

Or "unless I use the general-purpose warning-suppression escape". Things like the extra pair of parentheses around assignments in if statements are all very well, but really one would like an __I_meant_to_do_this(arbitrary C code) sort of construction which would work equally well against any warning, with which you could then liberally pepper your complicated macro setups.

(In a really ideal world it would also work equally well in any compiler, but the boat is well and truly missed on that one.)