https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80619
Bug ID: 80619
Summary: bad fix-it hint for GCC %lu directive with int
argument: %wu
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
When the %lu printf directive in a function decorated with attribute format
__gcc_diag__ is passed an int argument GCC issues a warning as expected, but
then proceeds to suggest to replace the directive with %wu. This suggestion is
wrong because %wu expects an unsigned HOST_WIDE_INT argument, a type that is
typically wider than int. The correct hint is "%u".
$ cat x.c && gcc -O2 -S -Wall -Wpedantic x.c
void f (const char*, ...) __attribute__ ((format (__gcc_diag__, 1, 2)));
void h (void)
{
f ("%lu", 0);
}
x.c: In function ‘h’:
x.c:5:9: warning: format ‘%lu’ expects argument of type ‘long unsigned int’,
but argument 2 has type ‘int’ [-Wformat=]
f ("%lu", 0);
~~^
%wu
