帮看下这个友元重载
class TriCoor
{
int x,y,z;
public:
TriCoor(int mx=0,int my=0,int mz=0);
TriCoor operator+(TriCoor t);
TriCoor& operator++();
//TriCoor& operator+=();
TriCoor& operator=(TriCoor t);
TriCoor operator-(TriCoor t);
friend ostream& operator<<(ostream &output,TriCoor &t);
friend istream& operator>>(istream &input,TriCoor &t);
int operator()()const;
TriCoor& operator--();
//int& operator[](int i)const;
void show();
void assign(int mx,int my,int mz);
};
TriCoor& TriCoor::operator=(TriCoor t)
{
x=t.x;y=t.y;z=t.z;
return *this;
}
friend istream& operator>>(istream &input,TriCoor &t)
{
input>>t.x>>t.y>>t.z;
return input;
}
请问下为什么在类中定义的输入输出流,在类外实现会出现错误,而只能在类中实现才不出错.