在类内访问2D数组时出错

Question

I have been working on a code in C++. But, I got stuck at a point.

This is a small prototype of my code::

#include <iostream>

using namespace std;

class Test{
private:
    const int var;
    void funPrivate(int arr[][var], int temp){
        cout << arr[0][0] << endl;
    }
public:
    Test(int n) : var(n){};

    void funPublic(){
        int a[var][var];
        funPrivate(a, var);
      cout << "Hello";
    };
};

int main()
{
    Test t1(5);
    t1.funPublic();
    return 0;
}

I create a class funPublic() method, where I create a 2D array (using the const int var, which I declare as a private member inside my class Test ) and then pass it to a private methode funPrivate(int arr[][var], int temp) , where I print arr[0][0] (which shall be a garbage value).

But, when I try to run this program, I get an error::

error: invalid use of non-static data member 'Test::var'

My method funPrivate(int arr[][var], int temp) is a normal function (not a static function) and I don't a reason that I shall declare int var as static. Why does this happen.

Further, if I slightly modify the declaration of my method 'funPrivate(int arr[][var], int temp)' to this void funPrivate(int arr[][var]) then I get one more error:

error: 'arr' was not declared in this scope

Now, I don't know why does that happen. We pass the size of the array for our convenience, because there is no way to determine the size of the array in a function, but that shall not cause the error that arr was not declared in this scope .

I have been thinking and searching a lot, but still can't find an answer. Please help. Thanks for any help in advance. :D

Answer 1

The member variable var cannot be used in the declaration of an array like you are attempting in the function funPrivate :

void funPrivate(int arr[][var], int temp)

Your best option is to use std::vector<std::vector<int>> .

void funPrivate(std::vector<std::vector<int>> const& arr, int temp) {
    cout << arr[0][0] << endl;
}

In the calling function, you can use:

void funPublic(){
    std::vector<std::vector<int>> arr(var, std::vector<int>(var));
    funPrivate(arr, var);
   cout << "Hello";
};