元素及其以外的指针算术。 此代码有什么问题？

Question

Please, what is wrong with this code. it's supposed to print until y[4] and then break out of the while loop, but it prints until y[12] and breaks thence; I think printing between y[5] to y[12] is wrong. It was taken from a website as an example that pointer arithmetic is limited to the elements of the array and one element beyond.

#include <stdio.h>

int main()
{
   int i = 0;
   int x[5] = {0, 1, 2, 3, 4};
   int y[5];
   int *ptr = x;
   while (&y[i] != (ptr+5)){
        y[i] = x[i];
        printf("Value of y[%d] is : %d\n", i, y[i]);
        i++;
   }

   return 0 ;
}

Answer 1

您的条件(&y[i] != (ptr+5)是错误的。Y是指向内存中与x完全不同的区域的数组。因此条件将保持为真。

Answer 2

The condition &y[i] != (ptr+5) does not make sense here. Why are you comparing y with ptr ? They are pointing to different memory locations. They can never be the same since they are pointing at two different locations. You just need to check for this:

while (i<5)

See full code here .

Answer 3

There is no guarantee that the array y will be placed at a specific position in relation to the array x . So what you are exploiting is compiler-specific behavior, that may change depending on compiler used, compiler version or even compiler flags.