在c ++中一个类有可能有一个成员是一个多维数组，其维度和范围在运行时之前是未知的？ [英] Is it possible in c++ for a class to have a member which is a multidimensional array whose dimensions and extents are not known until runtime?

问题描述

我最初问使用嵌套std： ：数组创建一个多维数组，直到运行时才知道维度或范围，但这有尝试使用std :: array完成它的XY问题。

问题 Boost.MultiArray的单行初始化和

The questions One-line initialiser for Boost.MultiArray and How do I make a multidimensional array of undetermined size a member of a class in c++? and their answers give some helpful information how to use Boost::MultiArray to avoid needing to know the extents of the dimensions at runtime, but fail to demonstrate how to have a class member that can store an array (created at runtime) whose dimensions and extents are not known until runtime.

推荐答案

只要避免使用多维数组：

Just avoid multidimensional arrays:

template<typename T>
class Matrix
{
    public:
    Matrix(unsigned m, unsigned n)
    :   n(n), data(m * n)
    {}

    T& operator ()(unsigned i, unsigned j)  {
        return data[ i * n + j ];
    }

    private:
    unsigned n;
    std::vector<T> data;
};

int main()
{
    Matrix<int> m(3, 5);
    m(0, 0) = 0;
    // ...
    return 0;
}

3D存取（在正确的3D矩阵中） >

A 3D access (in a proper 3D matrix) would be:

T& operator ()(unsigned i, unsigned j, unsigned k)  { 
    // Please optimize this (See @Alexandre C) 
    return data[ i*m*n + j*n + k ]; 
}

获取任意维度和范围将遵循该方案并添加重载范围信息）和/或利用可变参数模板。

Getting arbitrary dimensions and extent would follow the scheme and add overloads (and dimensional/extent information) and/or take advantage of variadic templates.

有很多维度可以在上面避免（即使在C ++ 11中），并且用std :: vector替换参数。例如：运算符（std :: vector indices）。
每个维度（除了最后一个）将有一个存储在向量n（作为上面2D示例中的第一个维度）的扩展。

Having a lot of dimensions you may avoid above (even in C++11) and replace the arguments by a std::vector. Eg: T& operator(std::vector indices). Each dimension (besides the last) would have an extend stored in a vector n (as the first dimension in the 2D example above).

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