https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104012
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Blocks| |85741
Status|UNCONFIRMED |RESOLVED
--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
I can reproduce the warning now with the command line options provided in
comment #4: -O0 and -Wformat-truncation=2 are needed to trigger it. The
interaction of the warning with optimizations (or their absence) is documented
in the manual:
When the exact number of bytes written by a format directive cannot be
determined at compile-time it is estimated based on heuristics that depend on
the level argument and on optimization. While enabling optimization will in
most cases improve the accuracy of the warning, it may also result in false
positives.
-Wformat-truncation=2
Level 2 warns also about calls to bounded functions whose return value is
used and that might result in truncation given an argument of sufficient length
or magnitude.
Not enabling optimization and using -Wformat-truncation=2 increases the chance
that the heuristic of assuming the argument with greatest magnitude (for %04d
it would be INT_MIN) will be used. GCC still does some value and range
propagation even at -O0 but it doesn't inline function calls (like those to
std::string members) or do other optimizations that might otherwise help it
track data flow more accurately. Regardless of optimization, the intent of
level 2 is to guide the programmer to provide a buffer that's big enough for
the largest possible output (i.e., you have to either prove to GCC that the
truncation isn't possible or handle it). At level 1 it's more like the other
way around (GCC has to prove that the call will result in truncation in order
to warn, although there's some fuzziness here and some heuristics apply as
well).
In short, this is not a bug.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85741
[Bug 85741] [meta-bug] bogus/missing -Wformat-overflow
