C语言 不定长数组

#include <stdio.h>
#include <malloc.h>

struct student {
    int age;
};

struct data {
    int len;
    // 不占用空间
    struct student students[0];
};

int main() {
    struct data* d = malloc(sizeof(struct data) + 2 * sizeof(struct student));
    d->len = 2;
    d->students[0].age = 10;
    d->students[1].age = 11;

    // 结果是4
    printf("%d\n", sizeof(struct data));
    // 内存对齐，结果是8
    printf("%d\n", sizeof(d));
    // 结果是0
    printf("%d\n", sizeof(d->students));

    free(d);
    return 0;
}