https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100842
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
In the call to strncpy the warning is suppressed because it's a common use case
to then add the nul byte (the suppression also only looks forward but not
backward).
Calling strncat like in the test program isn't a common use case so the warning
just points out that the copy truncates the string. This isn't a bug but a
design choice, analogous to -Wstringop-truncation warning about the same
problem in:
$ cat a.c && gcc -O2 -S -Wall a.c
char a[4];
void f (void)
{
char s[] = "test";
__builtin_snprintf (a, 3, "%s", s);
}
a.c: In function ‘f’:
a.c:6:30: warning: ‘%s’ directive output truncated writing 4 bytes into a
region of size 3 [-Wformat-truncation=]
6 | __builtin_snprintf (a, 3, "%s", s);
| ^~ ~
a.c:6:3: note: ‘__builtin_snprintf’ output 5 bytes into a destination of size 3
6 | __builtin_snprintf (a, 3, "%s", s);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
