How to pass a 2D array as a parameter in C?

A 2D array is essentially an array of arrays, where each element of the main array holds another array. In this article, we will see how to pass a 2D array to a function.

The simplest and most common method to pass 2D array to a function is by specifying the parameter as 2D array with row size and column size. One thing to note is that we always have to pass the size of the array's dimensions separately.

Let's take a look at an example:

#include <stdio.h>

// Funtion that takes 2d array as parameter
void print(int arr[3][3], int n, int m) {
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++)
            printf("%d ", arr[i][j]);
        printf("\n");
    }
}

int main() {
    int arr[3][3] = {{1, 2, 3},
                    {4, 5, 6},
                    {7, 8, 9}};
    
    // Passing the array along with the
    // size of rows and columns
    print(arr, 3, 3);

    return 0;
}

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Explanation: In this example, a 2D array arr is passed to the print function in the same way as it was declared but without the row size. The sizes of its dimensions are passed separately.

In the above method, the size of the row dimension can be omitted, and the program will still work.

#include <stdio.h>

// Funtion that takes 2d array as parameter
void print(int arr[][3], int n, int m) {
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++)
            printf("%d ", arr[i][j]);
        printf("\n");
    }
}

int main() {
    int arr[3][3] = {{1, 2, 3},
                    {4, 5, 6},
                    {7, 8, 9}};
    
    // Passing the array along with the
    // size of rows and columns
    print(arr, 3, 3);

    return 0;
}

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As Pointer to an Array

Arrays are decayed into pointers when passed to a function. So, we can directly specify the parameter of the function as pointer to an array of give size (column size).

#include <stdio.h>

// Funtion that takes 2d array as parameter
void print(int (*arr)[3], int n, int m) {
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++)
            printf("%d ", arr[i][j]);
        printf("\n");
    }
}

int main() {
    int arr[3][3] = {{1, 2, 3},
                    {4, 5, 6},
                    {7, 8, 9}};
    
    // Passing the array along with the
    // size of rows and columns
    print(arr, 3, 3);

    return 0;
}

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As Single Level Pointer

Internally, 2D arrays are stored sequentially either row after row or column after column. So, we can pass the 2D array as single level array if we know how elements are internally stored.

#include <stdio.h>
void print(int *arr, int rows, int cols) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++)
            printf("%d ", *(arr + i * cols + j));
        printf("\n");
    }
}

int main() {
    int arr[3][3] = {{1, 2, 3},
    {4, 5, 6},{7, 8, 9}};
    
    // Passing the array as a pointer along with
    // the size of rows and columns
    print((int *)arr, 3, 3);

    return 0;
}

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This method is not generally preferred as it is highly error prone.