How to Pass 2D Array to Functions in C++ ?

A two-dimensional array or a 2D array is an array having a collection of elements organized in rows and columns. It can be viewed as an array of arrays. 2D array can be visualized as a table or a grid, we can access elements of a 2D array using its row and column indices. In C++, we can pass a 2D array as an argument to a function.

Example of a 2D array

Below is an example of a 2D array having 3 rows and 2 columns.

int arr[3][2] = { 
    {10 , 20},
    {30 , 40},
    {50 , 60}, 
};

Passing a 2D Array Parameter to Functions in C++

In C++, arrays are always passed as pointers. The same goes for the two-dimensional arrays. There exist many ways of passing a 2D array to functions in C++.

Method 1: Passing 2D Array with Rows and Columns

return_type name (array_type array_name[rows][coloumns], int rows, int col)

Example

The below program demonstrates passing a 2D Array with a known number of rows and columns

C++

// C++ program to demonstrate passing of 2D Array with known
// number of rows and columns

#include <iostream>
using namespace std;

// function to print the array
void printArr(int arr[3][2], int n, int m)
{
    // iterating through 2D array and printing elements
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cout << arr[i][j] << " ";
        }
        cout << endl;
    }
}
int main()
{
    const int n = 3, m = 2;
    int arr[n][m] = { { 10, 15 }, { 20, 25 }, { 30, 35 } };

    // calling print function by passing array with row and
    // column size
    printArr(arr, n, m);
    return 0;
}

Output

10 15 
20 25 
30 35 

Note: We need to pass the dimensions of the array manually as the array loose the information about its dimensions due to array decay.

Method 2: Passing 2D Array with Rows and Columns Declared Globally.

return_type name (array_type array_name[rows][coloumns])

Example

The below program demonstrates passing a 2D Array with a known number of rows and columns that are declared globally.

C++

// C++ program to demonstrate passing of 2D Array When the
// number of rows and columns of a 2D array are known and
// declared globally
#include <iostream>
using namespace std;

// declaring global no of rows and cols
const int n = 3, m = 2;

// function to print an array
void printArr(int arr[n][m])
{
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cout << arr[i][j] << " ";
        }
        cout << endl;
    }
}
int main()
{

    int arr[n][m] = { { 10, 15 }, { 20, 25 }, { 30, 35 } };
    // calling print function
    printArr(arr);
    return 0;
}

Output

10 15 
20 25 
30 35 

Method 3: Passing 2D Array with only the Number of Columns

return_type name (array_type array_name[][coloumns])

or

return_type name (array_type (*array_name)[coloumns])

Example

The below program demonstrates passing a 2D Array with a known number of columns only.

C++

// C++ program to demonstrates the passing of 2D array When
// only the number of the column of a 2D array is Known.

#include <iostream>
using namespace std;

// function to print an array
void printArr(int arr[][2], int n, int m)
{

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cout << arr[i][j] << " ";
        }
        cout << endl;
    }
}
int main()
{

    int m = 2;
    int arr[][2]
        = { { 100, 105 }, { 120, 125 }, { 130, 135 } };

    // finding row size
    int n = sizeof arr / sizeof arr[0];
    // calling print function
    printArr(arr, n, m);
    return 0;
}

Output

100 105 
120 125 
130 135 

Note: We always need to mention the size of the column as it is mandatory for a 2D array because in C++, when a 2D array of n rows and m columns is declared, then in the memory a 1D array of size n x m is created.

Method 4: Passing 2D Array as a Single Pointer.

return_type function(array_type *arr,int row,int col)


//converting 2d array to pointer type by typecasting
// in function call
function((array_type *)array_name,row,col);

Example

The below program demonstrates passing a 2D Array as an argument using a single pointer.

C++

// C++ program to demonstrates passing a 2D Array as an
// argument using a single pointer.

#include <iostream>
using namespace std;

// function to print an array
void printArr(int* arr, int n, int m)
{
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {

            // printing the value of an element
            cout << *((arr + i * m) + j) << " ";
        }
        cout << endl;
    }
}
int main()
{

    int arr[][2] = { { 20, 25 }, { 30, 35 }, { 40, 45 } };
    int n = 3, m = 2;

    // calling print function
    printArr((int*)arr, n, m);
    return 0;
}

Output

20 25 
30 35 
40 45