ostream 运算符 <<不执行

Question

所以我自己编写了这段代码，但取自其他示例代码...

class A{
    friend std::ostream& operator<< (std::ostream& out, A& a);
    // Constructors, destructor, and variables have been declared
    // and initialized and all good.
}

std::ostream& operator<< (std::ostream& out, A& a){
    out << " this gets written " << endl; // it doesn't get executed
    return out;
}

int main(){
    A *_a = new A();
    return 0;
}

好吧，这只是不在控制台中打印 " this gets write "

Answer 1

如果您尝试通过 std::cout << 使用运算符a 或类似的东西，问题是您将指针传递给对象，而<<运算符被定义为采用 >对对象的引用。您需要将 a 声明为常规（非指针）A，或者使用 std::cout << *a。