Question

当在名称空间<<中为类Rectangle重载Shape时，我收到警告（但它有效）。请注意，我使用Clion生成了重载但仍然收到警告。

Rectangle.h

#include <ostream>

namespace Shape {

    class Rectangle {
    public:
        friend std::ostream &operator<<(std::ostream &os, const Rectangle &rectangle);
    };
}

Rectangle.cpp

#include "Rectangle.h"

using namespace Shape;

std::ostream& Shape::operator<<(std::ostream &os, const Rectangle &rectangle) {
    os << "rectangle";
    return os;
}

警告：

warning: 'std::ostream& Shape::operator<<(std::ostream&, const Shape::Rectangle&)' has not been declared within Shape
 std::ostream& Shape::operator<<(std::ostream &os, const Rectangle &rectangle) {
               ^~~~~

note: only here as a friend
         friend std::ostream &operator<<(std::ostream &os, const Rectangle &rectangle);
                              ^~~~~~~~

如何妥善处理，以免发出警告？谢谢

Answer 1

我找到了它！

您必须在命名空间内定义重载方法，而不是在类中。

#include <ostream>

    namespace Shape {

        class Rectangle {
        };
        std::ostream &operator<<(std::ostream &os, const Rectangle &rectangle);
    }

不是这样的：

#include <ostream>

    namespace Shape {

        class Rectangle {
        public:
            friend std::ostream &operator<<(std::ostream &os, const Rectangle &rectangle);
        };
    }

Answer 2

只需删除tuple：

Shape::

编辑：您还必须在std::ostream& operator<<(std::ostream &os, const Rectangle &rectangle) { os << "rectangle"; return os; }中封装重载的函数定义。

或者，您可以在namespace Shape {...}内声明operator<<()，但在namespace Shape之外声明：

Rectangle

重载运算符时的警告＆lt;＆lt;对于名称空间

2 个答案: