Theres loads of snprintf implementations lurking in
various libc but I believe the C9x standard differs from quite a few
especially in the return value. snprintf should return
the number of characters that would have been put into the
string (excluding the NULL char in this count). And also
allows snprintf to take 0 for its len so as to use snprintf
as a predictor for the final length of the string (which
implys that the buf can be NULL if the len is 0)
current non fully complient implementations are...
At least solaris & Mark Martinec's standalone snprintf 1.3
Does not take a NULL str and len 0, returns -1 for error in
this case, otherwise is perfect
At least Older glibc
returns -1 to flag an overflow, not the predicted length
At least Not quite as old glibc
returns the predicted count, but including the NULL char in this
count, i.e. returns correct+1
The sort of things Id expect knowing my fellow man
a) returning the actual number of chars put into the string, with or
without including terminating NULL's
b) in the case of overflow either terminating or not terminating
the string
Propose attached AC_FUNC_SNPRINTF which defines HAVE_SNPRINTF in the
case that the following test holds true
exit (!(3 <= snprintf(NULL,0,"%d",100)));
#if 0
/*I think this is unnecessarily punitive*/
exit (!(3 == snprintf(NULL,0,"%d",100)));
#endif
C.
P.S.
shouldn't there also be an AC_C_LONG_LONG ?
(http://www.csn.ul.ie/~caolan/publink/autoconf/ac_c_long_long.m4)
Real Life: Caolan McNamara * Doing: MSc in HCI
Work: [EMAIL PROTECTED] * Phone: +353-86-8790257
URL: http://www.csn.ul.ie/~caolan * Sig: an oblique strategy
Assemble some of the elements in a group and treat the group
dnl @synopsis AC_caolan_FUNC_SNPRINTF
dnl
dnl Provides a test for a fully C9x complient snprintf
dnl function.
dnl
dnl defines HAVE_SNPRINTF if it is found, and
dnl sets ac_cv_func_snprintf to yes, otherwise to no
dnl
dnl @version $Id$
dnl @author Caolan McNamara <[EMAIL PROTECTED]>
dnl
AC_DEFUN(AC_caolan_FUNC_SNPRINTF,
[AC_CACHE_CHECK(for working snprintf, ac_cv_func_snprintf,
[AC_TRY_RUN([#include <stdio.h>
int main () { exit (!(3 <= snprintf(NULL,0,"%d",100))); }
], ac_cv_func_snprintf=yes, ac_cv_func_snprintf=no,
ac_cv_func_snprintf=no)])
if test $ac_cv_func_snprintf = yes; then
AC_DEFINE(HAVE_SNPRINTF)
fi
])
