Struct变量使用printf更改值

Question

我有一个带有整数指针数组的结构.第一个指针的值在对printf的调用之间发生变化.除非我通过函数生成结构,否则不会发生这种情况.代码如下.有人能告诉我发生了什么吗？谢谢.

 struct a {

     int *nums[10];

 };

 struct a *makeS();


 int main(int argc, char *argv[]){

      struct a *_b = (struct a*) malloc(sizeof(struct a));

      struct a *_c = makeS();

      int i = 1;

      _b->nums[0] = &i;

      printf("Num is %d\n", *_b->nums[0]);  // prints 1
      printf("Num is %d\n", *_b->nums[0]);  // prints 1
      printf("Num is %d\n", *_b->nums[0]);  // prints 1
      printf("Num is %d\n", *_b->nums[0]);  // prints 1 … etc.


      printf("Num is %d\n", *_c->nums[0]);  // prints 1
      printf("Num is %d\n", *_c->nums[0]);  // prints 0
      printf("Num is %d\n", *_c->nums[0]);  // prints 0
      printf("Num is %d\n", *_c->nums[0]);  // prints 0 … etc.


  }

  struct a* makeS(){

      struct a *_s = (struct a*) malloc(sizeof(struct a));

      int i = 1;

      _s->nums[0] = &i;

      return _s;

 }

Answer 1

你的问题在于功能:

  struct a* makeS(){

      struct a *_s = (struct a*) malloc(sizeof(struct a));

      int i = 1;

      _s->nums[0] = &i;

      return _s;

 }

int i 超出范围,因为它是一个局部变量,这意味着您正在使用悬空指针.

所使用的内存i可以由其他东西自由使用,并且最有可能被后续printf调用中使用的缓冲区或工作空间重新调整.