在整数数组的情况下,指针减法究竟是如何工作的？

发布时间：2020-12-16 10:53:44 所属栏目：百科来源：网络整理

导读：#includestdio.hint main(){ int arr[] = {10,20,30,40,50,60}; int *ptr1 = arr; int *ptr2 = arr + 5; printf("Number of elements between two pointer are: %d.",(ptr2 - ptr1)); printf("Number of bytes between two pointers are: %d",(char*)ptr2 -

#include<stdio.h>
int main()
{
    int arr[] = {10,20,30,40,50,60};
    int *ptr1 = arr;
    int *ptr2 = arr + 5;
    printf("Number of elements between two pointer are: %d.",(ptr2 - ptr1));
    printf("Number of bytes between two pointers are: %d",(char*)ptr2 - (char*) ptr1);
    return 0;
}

对于第一个printf()语句,根据Pointer subtraction confusion,输出将为5

第二个printf()语句怎么样,输出是什么？

解决方法

引用C11,章节§6.5.6,附加运算符

When two pointers are subtracted,both shall point to elements of the same array object,or one past the last element of the array object; the result is the difference of the subscripts of the two array elements.

所以,当你在做的时候

printf("Number of elements between two pointer are: %d.",(ptr2 - ptr1));

ptr1和ptr2都是指向int的指针,因此它们给出了下标5中的差异.换句话说,地址的差异是参考sizeof(< type>)来计算的.

OTOH,

printf("Number of bytes between two pointers are: %d",(char*)ptr2 - (char*) ptr1);

ptr1和ptr2都被转换为指向char的指针,char的大小为1个字节.计算相应地进行.结果：20.

FWIW,请注意,减去两个指针会产生结果作为ptrdiff_t的类型,您应该使用％td格式说明符来打印结果.

（编辑：李大同）

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