贺老师的教学链接  本课讲解

用构造函数初始化对象

#include <iostream>
using namespace std;
class Time
{
public:
    Time( )
    {
        hour=0;
        minute=0;
        sec=0;
    }
    void set_time( );
    void show_time( );
private:
    int hour;
    int minute;
    int sec;
};
void Time::set_time( )
{
    cin>>hour;
    cin>>minute;
    cin>>sec;
}
void Time::show_time( )
{
    cout<<hour<<":"<<minute<<":"<<sec<<endl;
}
int main( )
{
    Time t1;
    t1.show_time( );
    Time t2;
    t1.set_time( );
    t2.show_time( );
    return 0;
}

在类外定义构造函数

class Time
{
public:
	 Time( );    
	 void set_time( ); 
	 void show_time( );  
  private:
	 int hour;  
	 int minute;
	 int sec;
};
Time::Time( )
{
  hour=0;                 
  minute=0;
  sec=0;
}
带参数的构造函数
class Time
{
public:
    Time();
    Time(int,int,int);
    void show_time();  
private:
    int hour;  
    int minute;
    int sec;
};
Time::Time()
{
    hour=0;                 
    minute=0;
    sec=0;
}

Time::Time(int h,int m,int s)     
{ 
     hour=h;   
     minute=m;
     sec=s;
}

int main()
{
    Time t1; //不可t1();         
    t1.show_time();


    Time t2(15,39,59);         
    t2.show_time();   
    return 0;
}

用参数初始化表对数据成员初始化
方便、简练的写法：用参数初始化表

class Time
{
public:
   Time( ):hour(0),minute(0),sec(0){};
   Time(int h,int m,int s):hour(h),minute(m),sec(s) {};
   ……
};

也可以在类外用参数初始化表定义构造函数。

Time::Time(int h,int m,int s):hour(h), minute(m), sec(s){};