Why isn‘t any warning for elements uninitialized in a Structure using Wuninitialized 

Why isn‘t any warning for elements  uninitialized in a Structure using Wuninitialized ？And uninitialized variables have warnings: https://godbolt.org/z/qPaYTrEnh

```c
#include<stdio.h>
#include<stdint.h>
#include<stdlib.h>

struct ab {
    int c;
    int d;
    int f;
};

int main() {
    int a;
    printf("%d", a);
    struct ab bc;
    printf("%d", bc.d);
    return 0;
}
```