On 07/07/2017 10:27 AM, Xi Ruoyao wrote:
On 2017-07-07 09:35 -0600, Martin Sebor wrote:
On 07/07/2017 07:05 AM, Basin Ilya wrote:
#include <stdio.h>
extern struct {
char s[142];
} x;
extern char s[142];
int main(int argc, char *argv[]) {
char buf[12];
sprintf(buf, "%c%s", 'x', x.s); // why warning?
sprintf(buf, "%s", x.s); // why no warning then?
sprintf(buf, "%c%s", 'x', s); // why no warning then?
return 0;
}
With GCC 8 I get a warning for the second call to sprintf for
the same reason at both -Wformat-overflow levels. I'm not sure
what prevents it in your case. Please open a new bug for it and
either attach the translation unit for your test case (obtained
by preprocessing it with with -E) or remove the #include and
declare sprintf or use __builtin_sprintf. (This should tell
us if the sprintf declaration in <stdio.h> is causing it.)
No. Using __builtin_sprintf still produces no warning with
GCC 7. I think it's a GCC 7 bug.
Ah, yes, I forgot. GCC 7 doesn't handle format strings consisting
solely of a single %s directive because it transforms such calls
to strcpy very early on, before the warning pass has a chance to
see them. It's fixed in GCC 8 under bug 77671.
Martin
