程序设计及引导-1.15.6指向结构变量的指针

// 随堂练习(程序设计).cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

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

#define STD_LENGTH 20
#define NUM 4


using namespace std;

struct Date {
	int nYear;
	int nMonth;
	int nDay;
};

struct StudentEx {
	unsigned ID;
	char szName[20];
	float fGPA;
	Date Birthday;
};

struct Student {
	unsigned ID;
	char szName[20];
	float fGPA;
};

struct Student MyClass[NUM] = {
	{1234,"TOM",3.78},
	{1238,"JACK",3.25},
	{1232,"MARY",4.00},
	{1237,"JONE",2.78}
};

int CompareID(const void* elem1, const void* elem2) {
	Student* ps1 = (Student*)elem1;  //强制类型转换
	Student* ps2 = (Student*)elem2;
	return ps1->ID  - ps2->ID;
}

int CompareName(const void* elem1, const void* elem2) {
	Student* ps1 = (Student*)elem1;
	Student* ps2 = (Student*)elem2;
	return strcmp(ps1->szName ,ps2->szName);
}


int main()
{
	qsort(MyClass, NUM, sizeof(Student), CompareID);
	for (size_t i = 0; i < NUM; i++)
		printf("%s\t", MyClass[i].szName);
	cout << endl;
	qsort(MyClass, NUM, sizeof(Student), CompareName);
	for (size_t i = 0; i < NUM; i++)
		printf("%s\t", MyClass[i].szName);
	return 0;
}