qsort函数的使用及其模拟实现

一.基本介绍

注意：qsort函数是默认从小到大排序

二、qsort 函数的使用

1.排序数组

cpp 复制代码

int compare(const void* e1, const void* e2)
{
    return  *(int*)e1 - *(int*)e2;//强制类型转换
}

int main()
{
    int arr[10] = { 44,5,34,56,42,90,43,1,52,98 };
    int num = sizeof(arr) / sizeof(arr[0]);
    int sz = sizeof(arr[0]);
    qsort(&arr[0], num, sz, compare);
    for (int i = 0; i < num; i++)
    {
        printf("%d ", arr[i]);
    }
    return 0;
}

结果：

2.排序结构体

（1）按结构体中的数字排序

cpp 复制代码

struct stu
{
    int age;
    char name[20];
}arr[3];


int compare(const void* e1, const void* e2)
{
    return  ((struct stu*)e1)->age - ((struct stu*)e2)->age;//强制类型转换
}

int main()
{
    struct stu arr[3] = { {13,"zhouzisong"},{12,"zhouzihao"},{20,"fengcheng"} };
    int num = sizeof(arr) / sizeof(arr[0]);
    int sz = sizeof(arr[0]);
    qsort(&arr[0], num, sz, compare);
    for (int i = 0; i < num; i++)
    {
        printf("%d %s\n",arr[i].age,arr[i].name);
    }
    return 0;
}

结果：

（2）按结构体中的字符串排序

cpp 复制代码

struct stu
{
    int age;
    char name[20];
}arr[3];


int compare_by_name(const void* e1, const void* e2)
{
    return  strcmp(((struct stu*)e1)->name , ((struct stu*)e2)->name);//强制类型转换
}


int main()
{
    struct stu arr[3] = { {13,"zhouzisong"},{12,"zhouzihao"},{20,"fengcheng"} };
    int num = sizeof(arr) / sizeof(arr[0]);
    int sz = sizeof(arr[0]);
    qsort(&arr[0], num, sz, compare_by_name);
    for (int i = 0; i < num; i++)
    {
        printf("%d %s\n",arr[i].age,arr[i].name);
    }
    return 0;
}

结果：

三、qsort 函数模拟实现

cpp 复制代码

struct stu
{
    int age;
    char name[20];
}arr[3];


int compare(const void* e1, const void* e2)
{
    return  ((struct stu*)e1)->age - ((struct stu*)e2)->age;//强制类型转换
}

int compare_by_name(const void* e1, const void* e2)
{
    return  strcmp(((struct stu*)e1)->name , ((struct stu*)e2)->name);//强制类型转换
}

void swap(char* bulf1, char* bulf2,int sz)
{
    int i;
    char temp;
    for (i = 0; i < sz; i++)
    {
        temp = *bulf1;
        *bulf1 = *bulf2;
        *bulf2 = temp;
        bulf1++;
        bulf2++;
    }
}

void my_qsort(void* base, size_t num, size_t sz, int (*cmp)(const void* e1, const void* e2))
{
    int i, j;
    for (i = 0; i < num - 1; i++)
    {
        for (j = 0; j < num - 1 - i; j++)
        {
            if (cmp((char*)base + j * sz, (char*)base + (j + 1) * sz) > 0)
            {
                swap( (char*)base + j * sz, (char*)base + (j + 1) * sz,sz);
            }
        }
    }
}

int main()
{
    struct stu arr[3] = { {13,"zhouzisong"},{12,"zhouzihao"},{20,"fengcheng"} };
    int num = sizeof(arr) / sizeof(arr[0]);
    int sz = sizeof(arr[0]);
    //my_qsort(&arr[0], num, sz, compare);
    my_qsort(&arr[0], num, sz, compare_by_name);
    for (int i = 0; i < num; i++)
    {
        printf("%d %s\n",arr[i].age,arr[i].name);
    }
    return 0;
}