函数指针的用法

#include<stdio.h>
#include<string.h>

int compare(void *, void *, int (*)(void *, void *));
int orderById(void *, void *);
int orderByName(void *, void *);
int orderByAge(void *, void *);

struct Student {
    int id;
    char name[64];
    int age;
    char address[1024];
};

void arrSort(struct Student *, int, int (*)(void *, void *));

int main(void)
{
    struct Student arr[5] = {{
        20140101,
            "zhangsan",
            24,
            "china.guangzhou"
    }, {
        20140103,
            "lisi",
            28,
            "USA.ny"
    }, {
        20140102,
            "wangwu",
            18,
            "UK"
        }, {
            20140110,
                "zhaoliu",
                19,
                "china.peking"
        }, {
            20140131,
                "fwy",
                27,
                "china.nc"
        }};

    printf("\n-----------id升序-----------------\n");
    arrSort(arr, 5, orderById);
    
    printf("\n-----------name升序-----------------\n");
    arrSort(arr, 5, orderByName);

    printf("\n-----------age升序-----------------\n");
    arrSort(arr, 5, orderByAge);
}

//统一比较函数
int compare(void * stu, void * stu2, int (*pt)(void *, void *))
{
    return (*pt)(stu, stu2);
}

//按Id升序排列
int orderById(void * stu, void * stu2)
{
    struct Student s = *((struct Student *)stu);
    struct Student s2 = *((struct Student *)stu2);

    return s2.id - s.id;
}

//按name升序排列
int orderByName(void * stu, void * stu2)
{
    struct Student s = *((struct Student *)stu);
    struct Student s2 = *((struct Student *)stu2);

    return strcmp(s2.name, s.name);
}

//按age升序排列
int orderByAge(void * stu, void * stu2)
{
    struct Student s = *((struct Student *)stu);
    struct Student s2 = *((struct Student *)stu2);

    return s2.age - s.age;
}

//结构体数组排序
void arrSort(struct Student * arr, int size, int (*pt)(void *, void *))
{
    int i,j;
    struct Student temp;

    for(i = 0; i < size -1; i++)
    {
        for(j = 0; j < size - 1 - i; j++)    
        {
            if(compare(&arr[j], &arr[j + 1], pt) < 0)
            {
                temp = arr[j];  
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
    }
    for(i = 0; i < size; i++)
    {
        printf("%10d %10s %3d %15s\n", arr[i].id, arr[i].name, arr[i].age, arr[i].address);
    }
}