零长度数组的应用

1. 例子

#include
#include
#include

typedef struct A
{
 int a;
 int b;
 int data[0];
}A_t;

struct B : public A_t
{
 int c;
 int d;
};
int mytest(int aaa, int bbb)
{
 struct A *aa = ( A_t *)malloc(sizeof(A_t) + sizeof(int)*bbb);
 aa->a = aaa;
 aa->b = bbb;
// memset(aa->data, 1, aa->b);

 struct B *bb = (struct B *)malloc(sizeof(struct B));
 bb->c = 3;
 bb->d = 4;

 aa = (struct A *)bb; //关键地方在这里
 struct B *cc = (struct B *)aa;

 

 printf("aa->a=%d\n",aa->a);
 printf("aa->b=%d\n",aa->b);
 printf("*********\n");
 printf("bb->a=%d\n",bb->a);
 printf("bb->b=%d\n",bb->b);
 printf("bb->c=%d\n",bb->c);
 printf("bb->d=%d\n",bb->d);
 printf("*********\n");
 printf("cc->a=%d\n",cc->a);
 printf("cc->b=%d\n",cc->b);
 printf("cc->c=%d\n",cc->c);
 printf("cc->d=%d\n",cc->d);
 
 return 0;
}

int main()
{
 mytest(1,2);
 return 0;
}

2. 运行结果

# ./qzzh
aa->a=0
aa->b=0
*********
bb->a=0
bb->b=0
bb->c=3
bb->d=4
*********
cc->a=0
cc->b=0
cc->c=3
cc->d=4
3.解释

struct A中的data[0]代表A可变长度，因此malloc时要把这长度一起malloc出来，这样就可以用了。