C数组中p [-2]的输出[重复]

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What does s[-1] = 0 mean? 6 answers

s [-1] = 0是什么意思? 6个答案

I was trying the below code snippet. Please help me in understanding how the o/p is coming as 2? What does p[-2] mean here?

我正在尝试下面的代码片段。请帮助我理解o / p如何成为2? p [-2]在这里是什么意思?

int main(void){
    int ary[4] = {1, 2, 3, 6};

    int *p = ary + 3; 

    printf("%d\n", p[-2]); 
}

2 个解决方案

#1

ary is an array of four ints. This will be put in memory like this:

ary是四个整数的数组。这将被放在内存中,如下所示:

 |  1  |  2  |  3  |  6  |
    ^     ^           ^
    |     |           |
   ary  p - 2         p

By saying p = ary + 3, you're setting p to the address of the fourth element in the array. So, p is pointing to 6. p[-2] is equal to *(p - 2). That means you point p to the second element in the array, and access its value: 2.

通过说p = ary + 3,你将p设置为数组中第四个元素的地址。因此,p指向6. p [-2]等于*(p-2)。这意味着您将p指向数组中的第二个元素,并访问其值:2。

#2

int *p = ary + 3 points to ary[3] so if you move the pointer two steps back you will get ary[1]

int * p = ary + 3指向ary [3]因此,如果你将指针向后移动两步,你将获得ary [1]

#1