https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126858
Bug ID: 126858
Summary: -Wanalyzer-use-of-uninitialized-value false positive
with printf's %n
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: analyzer
Assignee: dmalcolm at gcc dot gnu.org
Reporter: vincent-gcc at vinc17 dot net
Target Milestone: ---
Consider:
#include <stdio.h>
int main (void)
{
int n;
printf ("%n", &n);
return n != 0;
}
With gcc (Debian 20260725-1) 17.0.0 20260725 (experimental) [trunk
r17-2699-gf6b00aefc25], -fanalyzer gives:
tst.c: In function 'main':
tst.c:6:12: warning: use of uninitialized value 'n' [CWE-457]
[-Wanalyzer-use-of-uninitialized-value]
6 | return n != 0;
| ~~^~~~
'main': events 1-3
4 | int n;
| ^
| |
| (1) region created on stack here
| (2) capacity: 4 bytes
5 | printf ("%n", &n);
6 | return n != 0;
| ~~~~~~
| |
| (3) ⚠ use of uninitialized value 'n' here
while the purpose of "%n" with &n is to store the number of characters written
so far (i.e. 0) into the variable n. So n is necessarily initialized to 0
there.
