Initialising 2d array using 1 d array in c++

Question

Use of 2d array initialisation is forbidden and I am getting this error -

I am instructed to use main() as it is and i can only edit other two functions .

source.cpp(81): error C4700: uninitialized local variable 'Array' used
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Code:

int main(){
    int **Array;
    Array = getArray2D(10, 10, Array);
    for (int i = 0; i<10; i++)
    for (int j = 0; j<10; j++){
        Array[i][j] = 4;
    }
    cout << endl;

    for (int i = 0; i<10; i++){
        for (int j = 0; j<10; j++){
            cout << Array[i][j];
        }
        cout << endl;
    }
    getchar();

    return 0;
}



int* getArray1D(int n, int *A)
{
    A = new int[n];
    for (int i = 0; i < n; ++i)
        A[i] = 0;
    return A;
}
int** getArray2D(int m, int n, int** A)
{
    // m array of integers
    A = new int*[m];
    for (int i = 0; i < m; ++i)
    {
        // create a 1d array on each element of a A
        A[i] = getArray1D(n, A[i]);

    }
    return A;
}

How can i correct this ?

the error is self-explanatory - you Array in the first line isn't initialised. Use only getArray2D(10,10,Array). You may have problems with your pointer/variable type declaration — ha9u63a7
– ha9u63a7, Commented Nov 6, 2014 at 11:34
I am instructed to use main() as it is and i can only edit other two functions . — Divyanshu Jimmy
– Divyanshu Jimmy, Commented Nov 6, 2014 at 11:38
Then whoever instructed you doesn't have a good understanding of C++. — interjay
– interjay, Commented Nov 6, 2014 at 11:39
Its just a question to play with pointers and arrays , optimisation and overhead is tottaly ignored . — Divyanshu Jimmy
– Divyanshu Jimmy, Commented Nov 6, 2014 at 11:47

gsamaras · Accepted Answer · 2014-11-06 11:44:49Z

3

The problem is that you don't initialize the Array to NULL and then you use it.

So change this:

int **Array;
Array = getArray2D(10, 10, Array);

to this:

int **Array = NULL;
Array = getArray2D(10, 10, Array);

What you get is actually a warning, not an error, that looks like this:

warning: ‘Array’ is used uninitialized in this function [-Wuninitialized]

Don't forget to de allocate your memory later!

edited Nov 6, 2014 at 11:44

answered Nov 6, 2014 at 11:34

gsamaras

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8 Comments

interjay Over a year ago

This will remove the error message, but it isn't the correct fix. That parameter should not exist at all as the function doesn't use it.

gsamaras Over a year ago

The function uses the array @interjay. It could not use it and do it like this gsamaras.wordpress.com/code/2d-dynamic-array-c, but in the OP's code it is used inside the function.

interjay Over a year ago

No, it isn't used inside the function. The function overwrites the value that was passed in without using the original value.

Divyanshu Jimmy Over a year ago

I am instructed to use main() as it is .

gsamaras Over a year ago

Yes I agree @interjay. Jimmy yes I saw your comment under the question. So, with the suggest from my answer you overpass the problem you had?

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