[Bug libc/17089] New: error.c triggers -Wformat-extra-args

[dmacks at netspace dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17089

            Bug ID: 17089
           Summary: error.c triggers -Wformat-extra-args
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: dmacks at netspace dot org
                CC: drepper.fsp at gmail dot com

Building gettext-0.19.1 (which embeds copies of gnulib, which has error.c with
code from libc), on OS X 10.8, which uses the clang compiler (via XCode-5.1),
gives:

clang -DHAVE_CONFIG_H -DEXEEXT=\"\" -I. -I..  -I../intl -I../intl
  -DDEPENDS_ON_LIBICONV=1 -DDEPENDS_ON_LIBINTL=1  -I/sw/include  -Os -c -o
  error.o error.c
error.c:381:12: warning: data argument not used by format string
  [-Wformat-extra-args]
           file_name, line_number);

The same construct is still present in misc/error.c in glibc git at line 306
[1]:

#if _LIBC
  __fxprintf (NULL, file_name != NULL ? "%s:%d: " : " ",
              file_name, line_number);
#else
  fprintf (stderr, file_name != NULL ? "%s:%d: " : " ",
           file_name, line_number);
#endif

In the case where file_name==NULL, the format-string is " " but file_name and
line_number are still passed. This may not be a functional error [2], but it's
an easy-to-clear warning. Just have whole alternative fprintf() with
appropriate parameters in a conditional if/else block rather than just
conditional on the format-string. Something like:

  if (file_name != NULL)
    fprintf (stderr, "%s:%d: ", file_name, line_number)
  else
    fprintf (stderr, " ");


[1]
http://sourceware.org/git/?p=glibc.git;a=blob;f=misc/error.c;h=63bd309f22b7782474b72239ffa70e11a2b4b531;hb=HEAD
[2]
http://stackoverflow.com/questions/3578970/passing-too-many-arguments-to-printf

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