C语言快速排序函数用法（qsort）

#include <stdio.h>#include <stdlib.h>#include <string.h>struct student{  int id;  char name[12];  char sex;};int compare(const void* a,const void* b)//基本数据类型排序{  return *(char*)a-*(char*)b;//从小到大    //取值//强转为相应类型的指针！！}int compare_struct(const void* a,const void* b){  return (*(struct student*)a).id-((struct student*)b)->id;         //注意优先级诶！//否则报错在非结构体中。。。}int compare_struct_duoji(const void* a,const void* b)//多级排序{  struct student student_a=*(struct student*)a;  struct student student_b=*(struct student*)b;  if(student_a.id==student_b.id)  {    return student_a.sex-student_b.sex;  }  else  {    return student_a.id-student_b.id;  }}void main(){//*************char型*************  char a[5]="hello";  qsort(a,5,sizeof(a[0]),compare);      //元素个数//元素大小//函数指针  int i;  for(i=0;i<5;i++)      printf("%c ",a[i]);  printf("/n");//************struct型************  struct student e[4]={{100,"chen",'m'},{100,"li",'f'}, /             {70,"wang",'f'},{100,"zhang",'m'}};  qsort(e,4,sizeof(e[1]),compare_struct_duoji);  for(i=0;i<4;i++)      printf("%d %s %c/n",e[i].id,e[i].name,e[i].sex);}