预编译理解

来源:互联网 发布:妖怪名单实体娃娃 淘宝 编辑:程序博客网 时间:2024/05/19 14:52

废话少说,直接上代码:

#include <iostream>using namespace std;#define  MAX 0class Time{public:int hour;int minute;int sec;};void set_time(Time&t,int hour,int minute,int sec){t.hour = hour;t.minute = minute;t.sec = sec;}void show_time(Time& t){cout<<t.hour<<":"<<t.minute<<":"<<t.sec<<endl;}int main(){void set_time(Time&,int hour = 10,int minute = 0,int sec = 0);void show_time(Time&);#if MAX Time t1;set_time(t1,12,20,30);show_time(t1);#elseTime t2;set_time(t2);show_time(t2);#endifreturn 0;}
此时输出:


当把

#define  MAX 0
改成 
#define  MAX 1
代码如下:
#include <iostream>using namespace std;#define  MAX 1class Time{public:int hour;int minute;int sec;};void set_time(Time&t,int hour,int minute,int sec){t.hour = hour;t.minute = minute;t.sec = sec;}void show_time(Time& t){cout<<t.hour<<":"<<t.minute<<":"<<t.sec<<endl;}int main(){void set_time(Time&,int hour = 10,int minute = 0,int sec = 0);void show_time(Time&);#if MAX Time t1;set_time(t1,12,20,30);show_time(t1);#elseTime t2;set_time(t2);show_time(t2);#endifreturn 0;}

此时输出: