Question

我在Recursion部分阅读'ANSI-C编程语言'。我正在运行递归示例：

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

static int v[] = {1,3,6,1,2,3,6,89,3,5,7,2,3};
int size = sizeof(v)/sizeof(v[0]);

void sy_swap (int v[], int i, int j);
void sy_qsort(int v[], int left, int right);

/*Swap function*/
void sy_swap (int v[], int i, int j)
{
    int temp;
    temp = v[i];
    v[i] = v[j];
    v[j] = temp;
}

/*Sort function*/
void sy_qsort(int v[], int left, int right)
{
    int i, last;
    static int loop = 0;

    if(left >= right){  /*Finish sort*/
        return;
    }
    sy_swap(v, left, (left + right)/2); /*Move middle element to beginning of the half*/
    last = left;
    for(i = left+1; i<=right; i++){ /*After this loop, we have to half: smaller than 'middle element' and bigger*/
        if (v[i] < v[left]){
            sy_swap(v, ++last, i);
        }
    }
    sy_swap(v, left, last); /*Move 'middle element' to the head of SMALL half, to finish division the array into 2 half*/

    sy_qsort(v,left, last-1);   /*Sort Small Half*/
    sy_qsort(v, last+1, right); /*Sort Big Half*/

}

int main(void)
{
    int i = 0;

    printf("sizes: size of v=%d, size of v[0]=%d, total elements=%d\n",(int)sizeof(v), (int)sizeof(v[0]),size); /*Check 'size' before sort*/
    sy_qsort(v,0,size);
    printf("sizes: size of v=%d, size of v[0]=%d, total elements=%d\n",(int)sizeof(v), (int)sizeof(v[0]),size); /*Check 'size' after sort*/

    for (i =0; i<size; i++){
        printf("%d,",v[i]);
    }

    return (0);
}

有人知道为什么'size'变量在调用sort函数后被改变了，尽管sort函数中没有操作改变'right'参数？

这是结果显示'size'从实际的13（数组中的元素总数）更改为89（数组中的最大元素）

sizes: size of v=52, size of v[0]=4, total elements=13
sizes: size of v=52, size of v[0]=4, total **elements=89**
1,1,2,2,3,3,3,3,5,6,6,7,13,89,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0......

Answer 1

您有未定义的行为，因为您将数组的size包含为有效索引，而不是。

以循环

为例

for(i = left+1; i<=right; i++)

在sy_qsort函数的第一次main调用中，变量right等于size，这是数组的大小，但作为索引是超越的最后一个元素。条件必须是i < right。

为什么快速排序函数更改参数的值

1 个答案: