模板类中的友元函数使用注意

来源：互联网发布：软件可行性方案模板编辑：程序博客网时间：2024/06/16 00:32

<pre name="code" class="cpp">#ifndef TEMPLATETEST_H#define TEMPLATETEST_H#include <iostream>#include <string>using namespace std;class myException{    public:        myException(string s):info(s){};        string info;};template<class T> class Point;//模板类前置声明template<class T> istream& operator >> (istream& in,Point<T>& p);  //声明友元模板函数template<class T> ostream& operator << (ostream& out,Point<T> p);template<class T>class Point{    public:        Point():x(0),y(0){};        Point(T x,T y):x(x),y(y){};        void setX(T a);        void setY(T a);        T getX();        T getY();        ~Point(){};        Point operator+(Point& p);        Point operator-(Point& p);        Point operator*(T a);        Point operator/(T a);        friend  istream& operator >> <>(istream& in,Point<T>& p);        //注意在友元函数后加<>,一是，表明此友元函数是函数模板；二是，此模板使用的模板类型参数为当前模板类的类型参数class。        friend  ostream& operator << <>(ostream& out,Point<T> p);    private:        T x;        T y;};void templateTry();#endif // TEMPLATETEST_H

方法实现：

#include "templateTest.h"template<class T> void Point<T>::setX(T a){this->x=a;}template<class T> void Point<T>::setY(T a) {this->y=a;}template<class T> T Point<T>::getX(){return this->x;}template<class T> T Point<T>::getY(){return this->y;}template<class T> Point<T> Point<T>::operator+(Point& p){    Point<T> result;    result.setX(this->x+p.x);    result.setY(this->y+p.y);    return result;}template<class T> Point<T> Point<T>::operator-(Point& p){    Point<T> result;    result.setX(this->x-p.x);    result.setY(this->y-p.y);    return result;}template<class T> Point<T> Point<T>::operator*(T a){    Point<T> result;    result.setX(this->x*a);    result.setY(this->y*a);    return result;}template<class T> Point<T> Point<T>::operator/(T a){    Point<T> result;    if(0==a)    {        throw(new myException("Point operator / ,can not divice zero!"));    }    result.setX(this->x/a);    result.setY(this->y/a);    return result;}template<class T> istream& operator>>(istream& in,Point<T>& p){    T a,b;    in>>a>>b;    p.setX(a);    p.setY(b);    return in;}template<class T> ostream& operator<<(ostream& out,Point<T> p){    return out<<"("<<p.getX()<<","<<p.getY()<<")";}void templateTry(){    try{    Point<float> a(3,3),b;    cin>>b;    cout<<"a:"<<a<<endl;    cout<<"b:"<<b<<endl;    cout<<"a+b:"<<(a+b)<<endl;    cout<<"a-b:"<<(a-b)<<endl;    cout<<"a*100:"<<(a*100)<<endl;    cout<<"a/20:"<<(a/20)<<endl;    }    catch(myException* e)    {        cout<<e->info<<endl;    }}

运行结果：

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