检查结构数组的 NULL

Question

struct student
{
   int roll;
   char *name;
};

int main()
{
  int i;
  struct student arr[2];
  arr[0].roll = 12;
  arr[1].name = "John";

  arr[1].roll = 13;
  arr[1].name = "Craig";

  struct student *ptr;

  ptr=arr;

  // This is perfect.

  for(i = 0; i<2; i++)
  {
    printf("%d %s", ptr->roll, ptr->name);
  }

  // This is also ok.
   printf("%d %s", ptr->roll, ptr->name);

   ptr++ // getting to next structure.

   printf("%d %s", ptr->roll, ptr->name);

  // But this isn't ok

  while(*ptr || ptr->name != NULL)
  {
    ptr++;
  }

  return 0;
}

如何在while循环中检查指针？

Answer 1

ptr 指向一个数组，如果你递增它，ptr 开始指向一个非空的内存不足大小的数组。你可以这样做:

ptr = arr;
while (ptr <  (arr +  sizeof(arr)/sizeof(arr[0])) ){
   ptr++;
}

注意:此技术不适用于动态数组。

要了解此公式的含义，请阅读:Weird behavior when printing array in C?