重载运算符 << 可以打印出两个不同的函数吗？

Question

这是我的一小段代码：

Cord::Cord(int x, int y){

  x_ = x;
  y_ = y;
}
Cord::Cord(int x, int y, int z){
  x_ = x;
  y_ = y;
  z_ = z;
}
std::ostream& operator <<(std::ostream& out, Cord& x) {
  out << x.x_ << " " << x.y_ << " " << x.z_;
  return out;
}

对于我的两个函数重载，是否可以使运算符在 << 函数上重载。现在，如果我只使用 x 和 y 的函数，它也会打印出 z。有没有办法让 << 运算符打印出两个函数而不打印出 z 当我只有 x 和 y 或者这是不可能的？

Answer 1

您需要 z_ 的默认值。

Cord::Cord(int x, int y){
  x_ = x;
  y_ = y;
  z_ = 0; // If 0 is a good default value for z_
}

使用默认值，解决方案之一可能是

std::ostream& operator <<(std::ostream& out, Cord& x) {
  if(z_!= 0)  // If 0 is your default value for z
      out << x.x_ << " " << x.y_ << " " << x.z_;
  else
      out << x.x_ << " " << x.y_;
  return out;
}

请注意，您的代码设计不当。

更新：设计命题

了解 Encapsulation 和 Polymorphism

部分解决方案：

Coord2d.cpp

Coord2d::Coord2d(int x, int y){
  x_ = x;
  y_ = y;
}
int Coord2d::getX(){
  return x_;
}
int Coord2d::getY(){
  return y_;
}

std::ostream& operator <<(std::ostream& out, Coord2d& coords2d) {
  out << x.x_ << " " << x.y_;
}

Coord3d.cpp

Coord3d::Coord3d(int x, int y, int z){
  x_ = x;
  y_ = y;
  z_ = z;
}
int Coord3d::getX(){
  return x_;
}
int Coord3d::getY(){
  return y_;
}
int Coord3d::getZ(){
  return z_;
}
std::ostream& operator <<(std::ostream& out, Coord3d& coords3d) {
  out << x.x_ << " " << x.y_ << " " << x.z_;
}

Answer 2

使用 optional，您可以：

class Coord
{
public:
    Coord(int x, int y) : x(x), y(y) {}
    Coord(int x, int y, int z) : x(x), y(y), z(z) {}

    friend std::ostream& operator <<(std::ostream& out, const Coord& c)
    {
        out << c.x << " " << c.y;
        if (c.z) { out << " " << *c.z; }
        return out;
    }

private:
    int x;
    int y;
    boost::optional<int> z;
};

Live Demo

重载运算符 << 可以打印出两个不同的函数吗？

Overloading operator << Possible to print out two different functions?

c++

overloading

operator-overloading