2D array as instance variable of class

in the constructor I'm trying to do array = new array[arg1][arg2]

You need to specify the array type, like

array = new int[arg1][arg2];

Note that this works in C++11 only - when using older standards, the second array size needs to be const (which is probably not what you want).

There are also some additional articles discussing the same issue:

• Multi-Dimensional Arrays
• How to "new" a two-dimension array in C++?

Ideally, since you are using C++ anyway, you should use std::vector as proposed in another answer.

Vectors use a lot of overhead though, don't they? I'm trying to keep my memory use light. –

Start with std::vector. Once your application is running properly from a functional perspective, if you are still concerned about memory usage and/or performance, do benchmarking. If you properly encapsulate your 2D array in a class, you can always change the actual implementation of the array with no impact on the code which uses it.

Technically, if you want to make sure that you have one flat memory area which contains your array, you could use a 1-dimensional array to simulate a 2-dimensional array, like in the following code (just to get you the idea, certainly needs some improvement, especially copy construction and assignment operators are missing):

class Array2D {
private:
    int *array;
    int size1;

public:
    Array2D(int arg1, int arg2) {
        size1 = arg1;
        array = new int[arg1 * arg2];
    }

    ~Array2D() {
        delete[] array;
    }

    int& at(int i1, int i2) {
        return array[i1 * size1 + i2];
    }
};

int main() {
    Array2D array(10, 10);

    array.at(2, 2) = 42;
    std::cerr << array.at(2, 2);

    return 0;
}