从构造函数参数初始化类初始化列表中的const多维数组

Question

I have a class that includes a const 2d array of values, and I want to define this array when I call the constructor. I have been told using const on values that should never be changed is preferred, so I wanted to try it in this case.

class A {
  public:
    A(const int passedArray[2][2]) : memberArray(passedArray) {}
  private:
    const int memberArray[2][2];
};

const int passedArray[][2] = {
  {0,0},
  {0,1}
};

A a(passedArray); // fails with "incompatible types
                  //in assignment of 'const int (*)[2]' to 'const in[2][2]'
A a(&passedArray); // fails

This also fails with const int passedArray[2][2] = ... , with private: const int** memberArray , etc.

I know I have to use an initializer list because a constructor cannot change values of const. Is this possible at all on C++11?

Answer 1

Comments to your question has some good info.

After that here is the working code:

//g++  5.4.0

#include <iostream>

class A {

  public:
    A(int passedArray[2][2]) 
    {
        //USE STD COPY TO COPY THE ARRAYS. 
        std::copy(&passedArray[0][0], &passedArray[0][0]+4,&memberArray[0][0]);

        //PRINT VALUES TO TEST
        for (int i = 0; i < 2; i++)
        {
            for (int j = 0; j < 2; j++)
            {
                std::cout << memberArray[i][j] << std::endl;
            }           
        }
    }

  private:
    int memberArray[2][2];
};

int main()
{

     //INITIALIZE YOUR ARRAY
     int passedArray[2][2] = {
       {0,0},
       {0,1}
     };

     //CREATE OBJECT
     A a(passedArray); 
}

If your business need is to have a "const multi dimensional array in your class" you have to do it any one of the below ways.

class A {

  public:
    A(const int passedArray[2][2]) 
    {

    }

  private:
    const int memberArray[2][2] = {{5,6},{7,8}};   //INITIALIZE HERE
};

OR

class A {

  public:
    A(const int passedArray[2][2]) 
    {

    }

  private:
    //DECLARE STATIC HERE
    static const int memberArray[2][2];
};

//INTIALIZE HERE
const int A::memberArray[2][2] = {{5,6},{7,8}};