https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78304
Bug ID: 78304
Summary: -Wformat doesn't warn anymore for inttypes.h format
string argument type mismatches
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: mark at gcc dot gnu.org
Target Milestone: ---
For this program:
#include <inttypes.h>
#include <stdio.h>
int
main (int argc, char **argv)
{
size_t size = argc;
printf ("size: %" PRIu32 "\n", size);
return 0;
}
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11) warns when given -Wformat:
t.c: In function ‘main’:
t.c:8:3: warning: format ‘%u’ expects argument of type ‘unsigned int’, but
argument 2 has type ‘size_t’ [-Wformat=]
printf ("size: %" PRIu32 "\n", size);
^
gcc (GCC) 7.0.0 20161110 (experimental) doesn't give any warning with -Wformat.
Note that both versions do warn when using "size: %u\n" as format string:
t.c: In function ‘main’:
t.c:8:19: warning: format ‘%u’ expects argument of type ‘unsigned int’, but
argument 2 has type ‘size_t {aka long unsigned int}’ [-Wformat=]
printf ("size: %u\n", size);
~^
%lu
They also both warn when using normal string concatenation:
t.c: In function ‘main’:
t.c:8:11: warning: format ‘%u’ expects argument of type ‘unsigned int’, but
argument 2 has type ‘size_t {aka long unsigned int}’ [-Wformat=]
printf ("size: %" "u" "\n", size);
^~~~~~~~~
t.c:8:22: note: format string is defined here
printf ("size: %" "u" "\n", size);
~~~~^
%" "lu
They even both warn when doing the format string define in the file itself:
#include <stdio.h>
#define UFORMAT "u"
int
main (int argc, char **argv)
{
size_t size = argc;
printf ("size: %" UFORMAT "\n", size);
return 0;
}
But gcc 4.8.5 has a better warning message:
t.c: In function ‘main’:
t.c:9:3: warning: format ‘%u’ expects argument of type ‘unsigned int’, but
argument 2 has type ‘size_t’ [-Wformat=]
printf ("size: %" UFORMAT "\n", size);
^
While 7.0.0 gives the somewhat cryptic:
t.c: In function ‘main’:
t.c:3:18: warning: format ‘%u’ expects argument of type ‘unsigned int’, but
argument 2 has type ‘size_t {aka long unsigned int}’ [-Wformat=]
#define UFORMAT "u"
^
