qsort函数

qsort函数用法举例

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//数字比较函数
int cmp_num(const void* a, const void* b)
{
    return *(int*)a - *(int*)b;
}

//字符比较函数
int cmp_char(const void* a, const void* b)
{
    return *(char*)a - *(char*)b;
}

//字符串比较函数
int cmp_string(const void* a, const void* b)
{
    return strcmp((char*)a, (char*)b);
}

//结构体某个成员比较函数
struct Node
{
    double data;
    int other;
};
int cmp_struct(const void* a, const void* b)
{
    return (*(struct Node*)a).data > (*(struct Node*)b).data ? 1 : -1;
}

int main()
{
    int i;
    //1.对一维数组进行排序
    int n, *array;
    scanf("%d", &n);
    array = (int*)malloc(n*sizeof(int));
    for(i = 0; i < n; i++)
    {
        scanf("%d", (array+i));
    }
    qsort(array, n, sizeof(int), cmp_num);
    for(i = 0; i < n; i++)
    {
        printf("%d ", array[i]);
    }
    free(array);
    printf("

");

    //2.对二维数组进行排序
    int j;
    int array2[5][2] = {{57, 68}, {59, 52}, {72, 28}, {96, 33}, {24, 42}};
    qsort(array2, 5, sizeof(int)*2, cmp_num);
    for(i = 0; i < 5; i++)
    {
        for(j = 0; j < 2; j++)
        {
            printf("%d ", array2[i][j]);
        }
       printf("

");
    }

    //3.对字符进行排序
    char array3[] = "cdefba";
    qsort(array3, strlen(array3), sizeof(char), cmp_char);    //string.h
    for(i = 0; i < (int)strlen(array3); i++)
    {
        printf("%c ", array3[i]);
    }
    printf("

");

    //4.对字符串进行排序
    char array4[5][10] = {"this", "is", "my", "computer", "."};
    qsort(array4, 5, sizeof(array4[0]), cmp_string);
    for(i = 0; i < 5; i++)
    {
        printf("%s
", array4[i]);
    }
    printf("
");

    //5.对结构体某个成员进行排序
    struct Node array5[5] = {{3, 2}, {1.2, 5}, {1.1, 5}, {8.1, 9}, {5.7, 6}};
    qsort(array5, 5, sizeof(array5[0]), cmp_struct);
    for(i = 0; i < 5; i++)
    {
        printf("%f %d
", array5[i].data, array5[i].other);
    }
    return 0;
}

说明：
compare比较函数原型：compare( (void *) & elem1, (void *) & elem2 );

Compare函数的返回值	描述
<0	elem1将被排在elem2前面
0	elem1 等于 elem2
>0	elem1 将被排在elem2后面

本文参考链接：
http://baike.baidu.com/link?url=WcoVEm6e7Ocki-7Sd1wR58dK9k7RJzkGaczK_ff5qnFqnuT0viTQJdCZfBieJisp3lbN9xnMBx1Z8rNeC8Sexa