When does -Wmissing-field-initializers triggers warning?

Question

I know as the name says, it triggers when there are missing field initializers. But it didn't trigger any warnings for the following code.

#include <stdio.h>

struct test {
    int a, b, c;
};

void func(struct test test) {
    printf("%d, %d, %d\n", test.a, test.b, test.c);
}

int main() {
    func((struct test) {12, .a = 1, 12, .a = 13, .b = 13});
    return 0;
}

It compiles with no warnings when I run gcc test.c -Wmissing-field-initializers . And it prints out 13, 13, 0. Is this the default behaviour of -Wmissing-field-initializers?

Answer 1

From the documentation:

This option does not warn about designated initializers

try

#include <stdio.h>

struct test {
    int a, b, c;
};

void func(struct test test) {
    printf("%d, %d, %d\n", test.a, test.b, test.c);
}

int main() {
    func((struct test) {1, 2}); // Now you get a warning
    return 0;
}