C++ UB

// by @MikailBag
// the simple code compiles without any warnings under -Wall BUT
// ❯❯❯ ./test
// [1]    12892 segmentation fault (core dumped)  ./test

// However with Wextra it warns:
// ❯❯❯ gcc -Wextra -o test test.c
// test.c:16:1: warning: missing initializer for field ‘f3’ of ‘struct Foo’ [-Wmissing-field-initializers]
//  };
//  ^
// test.c:7:12: note: ‘f3’ declared here
//      void (*f3)(void);
//             ^~

#include <stdio.h>
struct Foo {
    void (*f1)(void);
    void (*f2)(void);
    void (*f3)(void);
};

void g1(void) { printf("g1"); }
void g2(void) { printf("g2"); }

static struct Foo foo = {
    g1,
    g2
};

int main() {
    foo.f1();
    foo.f2();
    foo.f3();
}