一文带你学会C语言中的qsort函数

#include<stdio.h>
#include<stdlib.h> 
int int_cmp(const void* e1,const void* e2)
{
    if(*(int*)e1 > *(int*)e2 )//先强制类型转换，在解引用进行比较
       return 1;
    else if(*(int*)e1 == *(int*)e2 )
       return 0;
    else 
       return -1;
}
int main()
{
    int i=0;
    int arr[10]={1,4,0,5,8,9,2,3,6,7};
    int sz=sizeof(arr)/sizeof(arr[0]);
    qsort(arr,sz,sizeof(arr[0]),int_cmp);
    for(i=0;i<sz;i++)
       printf("%d ",arr[i]);
    return 0;
}

#include<stdio.h>
#include<stdlib.h> 
int float_cmp(const void* e1,const void* e2)
{
    return *(float*)e1 - *(float*)e2;
}
int main()
{
    int i=0;
    float arr[5]={1.0,3.5,2.2,7.3,5.5};
    int sz=sizeof(arr)/sizeof(arr[0]);
    qsort(arr,sz,sizeof(arr[0]),float_cmp);
    for(i=0;i<sz;i++)
       printf("%.1f ",arr[i]);
    return 0;
}

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
 
struct student
{
    char name[10];
    int age;
};
 
//以名字来对结构体进行排序
int struct_cmp_byname(const void* e1, const void* e2)
{
    return strcmp(((struct student*)e1)->name, ((struct student*)e2)->name);
}
 
int main()
{
    int i=0;
    struct student stu[3] = { {"张三",20},{"李四",19},{"王五",18}};
    int sz = sizeof(stu) / sizeof(stu[0]);
    qsort(stu, sz, sizeof(stu[0]), struct_cmp_byname);
    for (i = 0; i < sz; i++)
    {
        printf("%s %d\n", stu[i].name, stu[i].age);
    }
}

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
 
struct student
{
    char name[10];
    int age;
};
 
//以年龄来对结构体进行排序
int struct_cmp_byage(const void* e1, const void* e2)
{
    return ((struct student*)e1)->age - ((struct student*)e2)->age;
}
 
int main()
{
    int i=0;
    struct student stu[3] = { {"张三",20},{"李四",19},{"王五",18}};
    int sz = sizeof(stu) / sizeof(stu[0]);
    qsort(stu, sz, sizeof(stu[0]), struct_cmp_byage);
    for (i = 0; i < sz; i++)
    {
        printf("%s %d\n", stu[i].name, stu[i].age);
    }
}