[TOC] # 友元函數,類內實現 ~~~ template<class NameType, class AgeType> class Maker { friend void printMaker(Maker<NameType, AgeType >& p) { cout << "友元函數,類內實現" << p.name << " " << p.age << endl; } public: Maker(NameType name, AgeType age) { this->name = name; this->age = age; } private: NameType name; AgeType age; }; void test01() { Maker<string, int> m1("abc", 18); printMaker(m1); } ~~~ # 友元函數在類外實現 ~~~ //提前聲明類,下面的聲明要用 template<class NameType, class AgeType> class Maker; //聲明下模板,下面要用 template<class NameType, class AgeType> void printMaker(Maker<NameType, AgeType> &p); template<class NameType, class AgeType> class Maker { //1. 在函數名和()之間加上<>,不然編譯器會認為是普通函數,加上<> friend void printMaker<>(Maker<NameType, AgeType >& p); public: Maker(NameType name, AgeType age) { this->name = name; this->age = age; } private: NameType name; AgeType age; }; //友元在類外實現需要寫成函數模板 template<class NameType, class AgeType> void printMaker(Maker<NameType, AgeType> &p) { cout << "類外實現的友元函數: " << p.name << " , " << p.age << endl; } void test01() { Maker<string, int> m1("abc", 18); printMaker(m1); } ~~~