如何正确重载 <<ostream 的运算符?

How to properly overload the lt;lt; operator for an ostream?(如何正确重载 lt;lt;ostream 的运算符?)

问题描述

我正在用 C++ 编写一个用于矩阵运算的小型矩阵库.但是我的编译器抱怨，之前没有.这段代码被搁置了 6 个月，在此期间我将我的计算机从 debian etch 升级到 lenny (g++ (Debian 4.3.2-1.1) 4.3.2) 但是我在使用相同 g++ 的 Ubuntu 系统上遇到了同样的问题.

I am writing a small matrix library in C++ for matrix operations. However my compiler complains, where before it did not. This code was left on a shelf for 6 months and in between I upgraded my computer from debian etch to lenny (g++ (Debian 4.3.2-1.1) 4.3.2 ) however I have the same problem on a Ubuntu system with the same g++.

这是我的矩阵类的相关部分:

Here is the relevant part of my matrix class:

namespace Math
{
    class Matrix
    {
    public:

        [...]

        friend std::ostream& operator<< (std::ostream& stream, const Matrix& matrix);
    }
}

和实现":

using namespace Math;

std::ostream& Matrix::operator <<(std::ostream& stream, const Matrix& matrix) {

    [...]

}

这是编译器给出的错误:

This is the error given by the compiler:

matrix.cpp:459: 错误:'std::ostream&Math::Matrix::operator<<(std::ostream&,const Math::Matrix&)' 必须取正好一个参数

matrix.cpp:459: error: 'std::ostream& Math::Matrix::operator<<(std::ostream&, const Math::Matrix&)' must take exactly one argument

我对这个错误有点困惑，但是在这 6 个月里做了很多 Java 之后，我的 C++ 再次变得有点生疏.:-)

I'm a bit confused by this error, but then again my C++ has gotten a bit rusty after doing lots of Java those 6 months. :-)

推荐答案

您已将函数声明为 friend.它不是班级的成员.您应该从实现中删除 Matrix::.friend 表示指定的函数(不是类的成员)可以访问私有成员变量.您实现该函数的方式就像是错误的 Matrix 类的实例方法.

You have declared your function as friend. It's not a member of the class. You should remove Matrix:: from the implementation. friend means that the specified function (which is not a member of the class) can access private member variables. The way you implemented the function is like an instance method for Matrix class which is wrong.

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