C ++：如何通过其构造函数的参数初始化类中的矩阵的维度？ [英] C++: how to initialize the dimensions of a matrix inside a class through parameters of its constructor?

问题描述

我需要帮助的东西真的很简单，这C ++使得很难。我创建了一个类，lattice，目的是初始化和处理一个矩阵。有以下私人成员：

I need help in something really simple, which C++ makes very difficult. I created a class, lattice, with the aim to initialize and treat a matrix. There are the following private members:

private unsigned dim;
private double matrix [dim][dim];

我想通过参数初始化类的构造函数中的变量dim，继续返回错误。我试图使昏暗的公共和静态和初始化它在主程序，但仍有问题。如何创建这个简单的类？

I would like to initialize the variable dim in the constructor of the class through a parameter, but the compiler continue to return errors. I tried to make dim public and static and initializing it in the main program, but there are still problems. How could I create this simple class?

此外，我还在类中实现了一些方法，以更新矩阵的值。是真的，在主程序中初始化一个类的对象，然后使用它的更新方法，矩阵的值只存储一次？

Moreover, I also implemented some methods in the class in order to update the values of the matrix. Is it true that, initializing an object of the class in a main program and then using its "updating" methods, the values of the matrix are stored only once?

谢谢

推荐答案

创建这样的类有三种方法（至少）：

There are (at least) three ways to create such a class:

• 使用模板

template<size_t dim>
class Matrix
{
   private:
     double matrix[dim][dim];
}

c> std :: vector （例如 valarray 也可以工作）

#include <vector>
class Matrix
{
   private:
     size_t dim;
     std::vector<std::vector<double> > matrix;
   public:
     Matrix(size_t dim_) : dim(dim_), matrix()
     {
       matrix.resize(dim);
       for ( size_t i = 0; i < dim; ++i )
          matrix[i].resize(dim);
     }
}

不推荐！）

with the use of plain arrays (I do not recommend that!)

class Matrix
{
   private:
     size_t dim;
     double** matrix;
   public:
     Matrix(size_t dim_) : dim(dim_), matrix()
     {
       matrix = new double*[dim];
       for ( size_t i = 0; i < dim; ++i )
          matrix[i] = new double[dim];
     }
     ~Matrix() // you need a destructor!
     {
       for ( size_t i = 0; i < dim; ++i )
          delete [] matrix[i];
       delete [] matrix;
     }
}

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