cin、cout的重载

ostream & operator<<(ostream &os,const A &a)//const A &a是为了避免复制函数的调用 ；ostream &o 相当于 cout 
{
    o<<a.x<<" "<<a.y;
    return os;
}//返回值设为ostream &是为了连续使用 << 

#include<iostream>
using namespace std;
class A
{
    int x;
    int y;
    public:
        A(int a=0,int b=0):x(a),y(b) {}
    friend ostream & operator<<(ostream & o,const A & a);//友元 
};
ostream & operator<<(ostream &o,const A &a)//const A &a是为了避免复制函数的调用 ；ostream &o 相当于 cout 
{
    o<<a.x<<" "<<a.y; 
}//返回值设为ostream &是为了连续使用 << 
int main()
{
    A a(1,2);
    cout<<a<<endl;
}

istream & operator>>(istream &is,A &a)
{
    is>>a.x>>a.y;
    return is;
}

#include<iostream>
using namespace std;
class A
{
    int x;
    int y;
    public:
        A(int a=0,int b=0):x(a),y(b) {}
        friend istream & operator>>(istream & is,A & a);
        friend ostream & operator<<(ostream & os,const A & a);//设置友元 是为了访问私有成员x,y 
};
ostream & operator<<(ostream &os,const A &a) 
{
    os<<a.x<<" "<<a.y; 
    return os;
} 
istream & operator>>(istream &is,A &a)
{
    is>>a.x>>a.y;
    return is;
}
int main()
{
    A a;
    cin>>a;
    cout<<a<<endl;
    return 0;
}