我的ostream和istream朋友功能无法访问私人班级成员 [英] My ostream and istream friend function can't access private class members

问题描述

我的代码:

matrix.h

#include <iostream>

class Matrix {
private:
    int row;
    int col;
    int **array;

public:
    Matrix();
    friend std::ostream& operator<<(ostream& output, const Matrix& m);
};

matrix.cpp

#include "matrix.h"
#include <iostream>

Matrix::Matrix()
{
    row = 3;
    col = 4;

    array = new int*[row];

    for (int i = 0; i < row; ++i)
    {
        array[i] = new int[col];
    }

    for (int i = 0; i < row; ++i)
    {
        for (int j = 0; j < col; ++j)
        {
            array[i][j] = 0;
        }
    }
}

std::ostream& operator<<(std::ostream& output, const Matrix& m)
{
    output << "\nDisplay elements of Matrix: " << std::endl;

    for (int i = 0; i < m.row; ++i)
    {
        for (int j = 0; j < m.col; ++j)
        {
            output << m.array[i][j] << " ";
        }
        output << std::endl;
    }

    return output;
}

main.cpp

#include "matrix.h"
#include <iostream>
using namespace std;

int main()
{
    Matrix a;
    cout << "Matrix a: " << a << endl;

    system("pause");
    return 0;
}

错误:

1. 成员"Matrix :: row"(在第3行matrix.h中声明)无法访问
2. 成员"Matrix :: col"(在第3行matrix.h中声明)不可访问
3. 成员"Matrix :: array"(在第3行matrix.h中声明)无法访问
4. 二进制'<<' :未找到采用矩阵"类型的右侧操作数的运算符
5. 'ostream':模棱两可的符号
6. 'istream':模棱两可的符号

我做错了什么? :(

**我已经编辑了问题，以给出像Barry建议的MCVE示例，并且还删除了像Slava建议的using namespace std.我仍然遇到相同的错误.

**Edited: I've editted the question to give a MCVE example like Barry suggested, and also removed using namespace std like Slava recommended. I'm still getting the same error.

推荐答案

既然您已经有了一个完整的示例，则在这里缺少std:::

Now that you have a complete example, you're missing std:: here:

friend std::ostream& operator<<(ostream& output, const Matrix& m);
                              ^^^

添加它，一切都可以正常编译:

Add it and everything compiles fine:

friend std::ostream& operator<<(std::ostream& output, const Matrix& m);

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