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ostream& operator<<(ostream& os,const class1& c);
//示例:
class {
//类内友元函数实现
friend ostream& operator<<(ostream& os,const class1& c){//类内实现
//
return os;
};
};
class2{
//类内声明(为友元)
friend ostream& operator<<(ostream& os,const class1& c);
};
//类外实现
ostream& operator<<(ostream& os,const class2& c){
//........................
return os;
}
PS:
ostream 最好加上 std::