Returning Arrays from the Function

Just like simple data types, arrays can be returned as function results.

However, there is a crucial limitation: only dynamic arrays can be returned from functions. This restriction arises from the local scope of functions; static arrays created within a function are only accessible within that function.

If you attempt to return a locally created array, you'll encounter a limitation due to the function's scope (you will try to return an address of non-existing variables that will lead to an error).

Returning a dynamic array

Why can we return dynamic arrays?
Unlike local variables, which are deallocated when a function exits, dynamic memory allocated using new[] allows data to survive beyond the scope of the function where it was created. As a result, we can access variables created inside the function using their addresses.
To return a dynamic array, we have to use the following type specifiers in the function signature:

dataType* for 1D array.
dataType** for 2D array.

Returning 1D array

main


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#include <iostream>

// Function to create and return a dynamic 1D array
int* createArray(const int size)
{
    int* arr = new int[size];
    for (int i = 0; i < size; ++i)
        arr[i] = i + 1; // Example initialization
    return arr;
}

int main()
{
    int size = 5;
    int* myArray = createArray(size);

    // Don't forget to delete the dynamically allocated memory
    delete[] myArray;
}

The function dynamically allocates memory for an integer array of the specified size. It initializes the array elements with values from 1 to the size of the array. The function returns a pointer on the first element of the dynamically allocated integer array that can now be used in the main() block.

Returning 2D array

main


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#include <iostream>

// Function to create and return a dynamic 2D array
int** createArray(const int rows, const int cols) {
    int** arr = new int*[rows];
    for (int i = 0; i < rows; ++i) {
        arr[i] = new int[cols];
        for (int j = 0; j < cols; ++j) {
            arr[i][j] = i * cols + j + 1; // Example initialization
        }
    }
    return arr;
}

int main() {
    int rows = 3;
    int cols = 2;
    int** myArray = createArray(rows, cols);
    
    // Use the returned 2D array
    for (int i = 0; i < rows; ++i) {
        for (int j = 0; j < cols; ++j) {
            std::cout << myArray[i][j] << " ";
        }
        std::cout << std::endl;
    }
    
    // Don't forget to delete the dynamically allocated memory
    for (int i = 0; i < rows; ++i) {
        delete[] myArray[i];
    }
    delete[] myArray;
    
    return 0;
}

The principle is the same as returning a 1D array: the only difference is that we have to return a pointer at the array of pointers using the int** type specifier to return the 2D array.

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