如何为C中的结构合理地分配内存？

struct Person {
    char name[20];
    int age;
};

int main() {
    struct Person p;
    // ...
}

struct Person {
    char* name;
    int age;
};

int main() {
    struct Person* p = (struct Person*)malloc(sizeof(struct Person));
    if (p != NULL) {
        p->name = (char*)malloc(20 * sizeof(char));
        // ...
    }
    // ...
    free(p->name);
    free(p);
}

struct Address {
    char city[20];
    char street[50];
};

struct Person {
    char name[20];
    int age;
    struct Address* address;
};

int main() {
    struct Person p;
    p.address = (struct Address*)malloc(sizeof(struct Address));
    // ...
    free(p.address);
}