https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125995
Bug ID: 125995
Summary: constexpr struct initialization leads to unexpected
results
Product: gcc
Version: 16.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: victarv at gmail dot com
Target Milestone: ---
The following code unexpectedly prints `-1`, instead of the expected `0`.
```
#include <stdint.h>
#include <stdio.h>
#include <string.h>
struct Foo {
uint8_t baz;
uint8_t qux;
};
struct Bar {
struct Foo foo;
};
static constexpr struct Bar b = {
.foo = {
.baz = 1
}
};
static void unused() {
struct Foo f = b.foo;
}
int main() {
uint8_t a = 1;
int diff = memcmp(&b.foo.baz, &a, 1);
printf("%d\n", diff);
return 0;
}
```
The following changes to the code fixes the issue:
1. Removing the `unused` function.
2. Explicitly assigning 0 to `qux` in the constexpr initializer.
3. Adding `struct Bar t = b;` in `unused`.
4. Changing `constexpr` to `const`.
Compiled with `gcc -std=c23`.
