使用回调函数实现类型c++的泛型算法

max 函数可以在任意一组对象中找出最大值，实现者并不知道怎样去比较两个对象的大小，调用者需要提供一个做比较操作的回调函数。

// generics.h
#ifndef GENERICS_H
#define GENERICS_H

typedef int (*cmp_t)(void *, void *);
extern void *max(void *data[], int num, cmp_t cmp);

#endif

// generics.c
#include "generics.h"

void *max(void *data[], int num, cmp_t cmp) {
    int i;
    void *temp = data[0];
    for(i = 1; i < num; i ++) {
        if(cmp(temp, data[i]) < 0) {
            temp = data[i];
        }
    }
    return temp;
}

// genericsMain.c
#include <stdio.h>
#include "generics.h"

typedef struct {
    const char *name;
    int score;
} student_t;

int comple_int(void *a, void *b) {
    if((int *)a > (int *)b) 
        return 1;
    else if((int *)a == (int *)b) 
        return 0;
    else 
        return -1;  
}

int cmp_student(void *a, void *b) {
    if(((student_t *)a)->score > ((student_t *)b)->score )
        return 1;
    else if (((student_t *)a)->score == ((student_t *)b)->score ) 
        return 0;
    else
        return -1;
}

int main(void) {
    int data[5] = {1, 3, 6, 4, 8};
    int *pdata[5] = {&data[0], &data[1], &data[2], &data[3], &data[4]};
    int *presult = max((void **)pdata, 5, comple_int);    
    printf("result %d\n", *presult);

    student_t list[4] = {{"Tom", 68}, {"Jerry", 72}, {"Moby", 60}, {"Kirby", 89}};
    student_t *plist[4] = {&list[0], &list[1], &list[2], &list[3]};
    student_t *pmax = max((void **)plist, 4, cmp_student);
    printf("%s %d\n", pmax->name, pmax->score);

    return 0;
}