转载自：
https://blog.csdn.net/wwzhang0307/article/details/53008806
#include <iostream> using namespace std; /*模板类 各种函数在类外的实现*/ template <typename T> class AA { public: AA(T a, T b); void printAA(); AA operator+(AA &tmp); //友元函数重载<< friend ostream& operator<< <T>(ostream& out, AA<T>& tmp); private: T a; T b; }; template <typename T> AA<T>::AA(T a, T b) { this->a = a; this->b = b; } template <typename T> void AA<T>::printAA() { cout << "a:" << a << " b:" << b << endl; } //类外实现函数时，加T的地方有 函数返回值，类名:: ，形参变量 template <typename T> AA<T> AA<T>::operator+(AA<T> &tmp) { AA tt(this->a + tmp.a, this->b + tmp.b); return tt; } //友元函数重载<< template <typename T> ostream& operator<< (ostream& out, AA<T>& tmp) { out << "a=" << tmp.a << " b=" << tmp.b << endl; return out; } int main() { AA<int> tmp(5, 6); AA<int> tmp1(5, 7); AA<int> tmp2 = tmp1 + tmp; tmp2.printAA(); cout << tmp2 << endl; return 0; }