Question

我对C ++很陌生，我对std :: map有疑问。对于学校项目，我必须在地图中存储空心矩阵（仅存储非零元素），因此我必须创建与矩阵中的坐标对应的类IJ。最后，我有这个：

std::map<IJ, std::complex<double>> matrix;

我已经重载了运算符==和运算符＆lt;如下：

bool IJ::operator==(const IJ& other) const{
return (this->i == other.getI() && this->j == other.getJ());
}

bool IJ::operator<(const IJ& other) const{
    return (this->i < other.getI() || (this->i == other.getI() && this->j < other.getJ()));
}

我检查过：他们工作正常。但是我在显示地图时遇到了麻烦。我尝试使用find（为了有一个const方法），at（这给了我同样的问题）但它没有工作，并且没有更好的结果与operator []。他们在这里：

// Display using find
for(int i = 1; i <= 3; i++){
    for(int j = 1; j <= 3; j++){
        if(matrix.find(IJ(i, j)) != matrix.end())
            std::cout << (matrix.find(IJ(i, j)))->second << " ";
        else
            std::cout << "(0.0,0.0) ";
    }
    std::cout << std::endl;
}
std::cout << std::endl;
// Display using operator[]
for(int i = 1; i <= 3; i++){
    for(int j = 1; j <= 3; j++){
        std::cout << matrix[IJ(i, j)] << " ";
    }
    std::cout << std::endl;
}
std::cout << std::endl;

以下是发生的事情：

// Tests of the operators :
std::cout << (IJ(1,1) == IJ(1,1)) << std::endl; // 1
std::cout << (IJ(1,1) == IJ(2,1)) << std::endl; // 0
std::cout << (IJ(1,1) < IJ(1,1)) << std::endl; // 0
std::cout << (IJ(1,4) < IJ(1,3)) << std::endl; // 0
std::cout << (IJ(2,2) < IJ(3,1)) << std::endl; // 1
// Filling the matrix and displaying it step by step (operator[] on the left and find on the right)
matrix[IJ(1, 1)] = 1;
/*(1,0) (0,0) (0,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) 
  (1,0) (0,0) (0,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) 
  (1,0) (0,0) (0,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) */
matrix[IJ(2, 3)] = 4;
/*(1,0) (0,0) (4,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) 
  (1,0) (0,0) (4,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) 
  (1,0) (0,0) (4,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) */
matrix[IJ(3, 3)] = 2;
/*(1,0) (0,0) (2,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) 
  (1,0) (0,0) (2,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) 
  (1,0) (0,0) (2,0)  (0.0,0.0) (0.0,0.0) (0.0,0.0) */

对于记录，创建IJ ij(1,1);然后执行matrix[ij] = 1会得到相同的结果。我猜测运算符[]的问题来自于我的一个愚蠢的错误，但我对find方法感到困惑。我发现了一些其他主题，但问题主要来自使用char *而不是string作为键和来自重载的运算符。非常感谢任何帮助，谢谢！

C ++ std :: map find不能用自定义对象作为键

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