继承中的重载问题，求指教！！！

[ilovecpp111]

Shape * shapes[4];

// initialize vector with Shapes
shapes[ 0 ] = new Circle( 3.5, 6, 9 );
shapes[ 1 ] = new Square( 12, 2, 2 );
shapes[ 2 ] = new Sphere( 5, 1.5, 4.5 );
shapes[ 3 ] = new Cube( 2.2 );

// output Shape objects and display area and volume as appropriate
for ( int i = 0; i < 4; i++ )
{cout << *( shapes[ i ] ) << endl;}

Shape类被Circle 等四个类继承，现在需要重载<< 而我想用虚函数virtual来对<<进行重载，但是重载的函数不能被同时声明为
friend和virtual ，，，请问这个问题要怎么解决？

[iyomumx]

class Shape
{
public:
    virtual ostream& print(ostream& os) const { /*子类重写这个函数*/ }
    friend ostream& operator<<(ostream& os, const Shape& obj) { return obj.print(os); }
};

[dustpg]

struct Shape {
    virtual ~Shape() noexcept { }
    virtual void out(std::ostream& os) const = 0;
};

auto operator <<(std::ostream& os, const Shape& s) -> std::ostream& {
    s.out(os); return os;
}

建议这样写(返回void)，返回 std::ostream这个对象本身就是为了方便代码编写，也方便编译器优化， 假设那个虚函数返回这个对象(std::ostream)，不方便编译器优化..

[flying_music]

引用 1 楼 iyomumx 的回复:

class Shape
{
public:
    virtual ostream& print(ostream& os) const { /*子类重写这个函数*/ }
    friend ostream& operator<<(ostream& os, const Shape& obj) { return obj.print(os); }
};

长见识了

[ilovecpp111]

引用 1 楼 iyomumx 的回复:

class Shape
{
public:
    virtual ostream& print(ostream& os) const { /*子类重写这个函数*/ }
    friend ostream& operator<<(ostream& os, const Shape& obj) { return obj.print(os); }
};

virtual ostream& print(ostream& os) const { /*子类重写这个函数*/ } 这个函数要renturn什么呢？是要return os吗？

[yuzhe22]

引用 1 楼 iyomumx 的回复:

class Shape
{
public:
    virtual ostream& print(ostream& os) const { /*子类重写这个函数*/ }
    friend ostream& operator<<(ostream& os, const Shape& obj) { return obj.print(os); }
};

你都在类中写了,你还用友员干吗?

[ilovecpp111]

引用 5 楼 yuzhe22 的回复:

[quote=引用 1 楼 iyomumx 的回复:]

class Shape
{
public:
    virtual ostream& print(ostream& os) const { /*子类重写这个函数*/ }
    friend ostream& operator<<(ostream& os, const Shape& obj) { return obj.print(os); }
};

你都在类中写了,你还用友员干吗?[/quote] 在类中也必须要用友元

[zycxnanwang]

引用 1 楼 iyomumx的回复:

class Shape
{
public:
    virtual ostream& print(ostream& os) const { /*子类重写这个函数*/ }
    friend ostream& operator<<(ostream& os, const Shape& obj) { return obj.print(os); }
};

学习了,,,,