问C语言。奇异函数行为

EN

#include <stdio.h>
#include <stdlib.h>

#define lambda(return_type, function_body) \
    ({ \
        return_type __fn__ function_body \
        __fn__; \
    })

void init(void (**fn)()){
    int num = 1337;
    *fn = lambda(void,(){printf("%d\n",num);});
}

int main(){
    void (*fn)();
    init(&fn);
    fn(); // Everything is fine, it prints '1337'
    fn(); // It prints '-1869573949' , maybe accessing memory somewhere
    fn(); // It does not print anything at all
    ...   // It does not print anything at all
    return 0;
}

void init(void (**fn)()){
    int num = 1337;
    *fn = lambda(void,(){printf("%d\n",num);});
}

void init(void (**fn)()){
    *fn = lambda(void,(){printf("%d\n",1337);});
}