Compiler error while declaring a matrix as a class member using a const variable as dimensions

Question

I have a class defined as

class A{

public :
    A(const int arg){
        x = arg;
    }
    const int x;
    int arr[x][x];
};

but the compiler gives

error : invalid use of non-static data member 'A::x'|

but as I declare x as static const int x

error: array bound is not an integer constant before ']' token|

Any solutions to this.

EDIT : The question has been marked as duplicate of another, but that question is more of concept, it doesn't provide a solution to it. I know the difference but I don't know the solution to the problem except for vectors, which is also mentioned in one of the answers too.

And remove the duplicate flag, since this is different than the post this question is marked as duplicate of.

Thanks.

It needs to be const at compile-time, not run-time. This is the kind of thing templates are for. — , Jun 10 '18 at 16:33
@NeilButterworth can you explain how can I use templates here. — Nilesh Kumar, Jun 11 '18 at 04:46

score 0 · Answer 1 · answered Jun 10 '18 at 16:35

First of all, no you don't declare x as static const int. Secondly the creation of the arrays is done at compile time while you assign to x at run time.

To solve your problem, use std::vector instead:

struct A {
    std::vector<std::vector<int>> arr;

    A(int arg)
        : arr(arg, std::vector<int>(arg))
    {}
};

Compiler error while declaring a matrix as a class member using a const variable as dimensions

1 Answers1