bash-3.2$ cat /tmp/x.c
struct a {
	int a;
};

struct b {
	struct a a;
};

int main() {
	struct b b;
	b.a.a = 1;
	const struct b *bptr = &b;
	struct a *a = &bptr->a;
	return a->a;
}
bash-3.2$ gcc -o /tmp/x2 /tmp/x.c -Wall
/tmp/x.c:13:12: warning: initializing 'struct a *' with an expression of type 'const struct a *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
        struct a *a = &bptr->a;
                  ^   ~~~~~~~~
1 warning generated.