如何利用C语言中的qsort库函数实现快速排序

偏执的太偏执、 2022-04-18 00:36 208阅读 0赞

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之前，我们已经写过快速排序的程序，而在C语言的库函数中就有快速排序的库函数，即为qsort, 其用法如下：

功 能： 快速排序

头文件：stdlib.h

用 法： void qsort(void \*base,int nelem,int width,int (\*fcmp)(const void \*,const void \*));

参数：

1 待排序数组首元素的地址

2 数组中待排序元素数量

3 各元素的占用空间大小

4 指向函数的指针，用于确定排序的顺序

示例程序如下：

#include <stdio.h>#include <stdlib.h>int compInc(const void *a, const void *b){ return *(int *)a - *(int *)b;}int compDec(const void *a, const void *b){ return *(int *)b - *(int *)a;}int main(){ int a[5] = {
         11,2,13,4,7}; int b[5] = {
         11,2,13,4,7}; int len = 5; int i; printf("递增排序结果:\n"); qsort(a, len, sizeof(a[0]), compInc); for(i = 0; i < len; i ++) {  printf("%d ", a[i]); } printf("\n\n"); printf("递减排序结果:\n"); qsort(b, len, sizeof(b[0]), compDec);   for(i = 0; i < len; i ++) {    printf("%d ", b[i]); } printf("\n"); return 0;}

结果为：

递增排序结果:  
2 4 7 11 13  
  
递减排序结果:  
13 11 7 4 2  
  
  
      下面，继续看qsort的一些用法：

#include <stdio.h>#include <stdlib.h>#include <string.h>#define M 12#define N 20int compareInc(const void *a, const void *b){ return strlen((char *)a) - strlen((char*)b);}int compareDec(const void *a, const void *b){ return strlen((char *)b) - strlen((char*)a);}int main(void){ int i; char s[M][N]= { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" }; qsort(s, M, sizeof(char) * N, compareInc); for(i = 0;i < M; i++)  printf("%s\n", s[i]); printf("\n"); qsort(s, M, sizeof(char) * N, compareDec); for(i = 0;i < M; i++)  printf("%s\n", s[i]); return 0;}

结果为：

May  
July  
June  
March  
April  
August  
October  
January  
December  
November  
February  
September  
  
September  
February  
November  
December  
October  
January  
August  
April  
March  
June  
July  
May

#include <stdio.h>#include <stdlib.h>#include <string.h>#define M 12#define N 20int compare1(const void *a, const void *b){ return *(char *)a - *(char*)b;}int compare2(const void *a, const void *b){ return *(char *)b - *(char*)a;}int main(void){ int i; char s[M][N]= { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" }; qsort(s, M, sizeof(char) * N, compare1); for(i = 0;i < M; i++)  printf("%s\n", s[i]); printf("\n"); qsort(s, M, sizeof(char) * N, compare2); for(i = 0;i < M; i++)  printf("%s\n", s[i]); return 0;}

结果为：

April  
August  
December  
February  
July  
June  
January  
March  
May  
November  
October  
September  
  
September  
October  
November  
May  
March  
June  
July  
January  
February  
December  
August  
April  
  
  
       好，欣赏最后一个qsort程序：

#include <stdio.h>#include <stdlib.h>#define N 6typedef struct{     char name[15];    int  score;}Student;int compare1(const void *a,const void *b){    return ((Student*)a)->score - ((Student*)b)->score;}int compare2(const void *a,const void *b){    return *(((Student*)a)->name) - *(((Student*)b)->name);}void print(Student s){ printf("%-15s : %d\n", s.name, s.score);}int main(){    Student s[N] = { "Zhang San", 94, "Li Si",     80, "You",       94, "I",        100, "He",        72, "She",       60 }; int i; qsort(s, N, sizeof(Student), compare1); for(i = 0; i < N; i++) {  print(s[i]); } printf("\n"); qsort(s, N, sizeof(Student), compare2); for(i = 0; i < N; i++) {  print(s[i]); } return 0;}

结果为：

She             : 60  
He              : 72  
Li Si           : 80  
You             : 94  
Zhang San       : 94  
I               : 100  
  
He              : 72  
I               : 100  
Li Si           : 80  
She             : 60  
You             : 94  
Zhang San       : 94

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