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

[pm215]

The gcc mailing list post giving the original patch to add -Wformat-zero-length explains why it's there: this used to be a standard part of -Wformat and the patch submitter wanted to be able to turn it off without turning off all of -Wformat (for exactly the kind of reasons you give :-)). It's on by default because they didn't want to change the default behaviour from gcc 2.95:

mnementh$ gcc-2.95 -Wall -c t.c
t.c: In function `main':
t.c:2: warning: zero-length format string
mnementh$ gcc-2.95 --version
2.95.4

and also because "There are lots of other checks for useless formats (e.g., for using useless combinations of flag characters where one gets ignored)".

[pm215]

...since this came up on irc again today, I looked through some older gcc releases. "zero-length format string" has been warned about since gcc 2.0 (gcc 1.42 has no format string checking at all). Whenever this came in it seems to be before the dawn of gcc's online svn repo history.

GCC bug

[andersk.livejournal.com]

You should all add your thoughts to GCC bug 47901 “-Wall should not imply -Wformat-zero-length by default” (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47901).