C语言中使用qsort()

        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 20


int 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 20


int 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 6

typedef 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