如何正确地重载<<操作员为ostream？ [英] How to properly overload the << operator for an ostream?

问题描述

我在C ++中为矩阵操作编写了一个小矩阵库。但是我的编译器抱怨，之前它没有。这个代码留在货架上6个月，在我将我的计算机从debian蚀刻升级到lenny（g ++（Debian 4.3.2-1.1）4.3.2
）然而我在Ubuntu系统上有同样的问题具有相同的g ++。

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);
    }
}

b
$ b

And the "implementation":

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：error：'std :: ostream&
Math :: Matrix :: operator<<（std :: ostream& amp;
const Math :: Matrix&）必须接受
一个参数

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

我对这个错误感到困惑，但是我的C ++在这6个月之后做了大量的Java之后又有点生锈了。 ： - ）

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

您已将您的函数声明为 friend 。它不是类的成员。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。实现该函数的方法就像一个 Matrix 类的实例方法错误。

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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