Passing 2D arrays as arguments in CPP

Ways to pass a 2D array to a function are as follows:-

When both dimensions are available globally.

Code:

C++ Code

#include <bits/stdc++.h>
const int n = 3, m = 3;

void display(int nums[n][m]){
	for(int i = 0; i<n; i++){
		for(int j = 0; j<m; j++)
			std::cout << nums[i][j] << ' ';
		std::cout << std::endl;
	}
}
int main(){
	int nums[n][m] = {{1 ,2 ,3}, {4, 5, 6}, {7, 8, 9}};
	display(nums);
}

Output:

1 2 3
4 5 6
7 8 9

When only column size is available globally.

Code:

C++ Code

#include <bits/stdc++.h>
const int m = 3;
void display(int arr[][m], int n){
      for(int i = 0; i<n; i++){
	   for(int j = 0; j<m; j++)
		std::cout << arr[i][j] <<  " ";
	   std::cout << std::endl;
      }
}
int main(){
	int arr[][m] = {{1 ,2 ,3}, {4, 5, 6}, {7, 8, 9}};
	display(arr, 3);
}

Output:

1 2 3
4 5 6
7 8 9

If your compiler is C99 compatible then passing of variable-sized arrays are allowed. We do it by passing the variable-sized dimensions.

Code:

C Code

#include <stdio.h>
void display(int r, int c, int arr[][c]){
	for(int i = 0; i<r; i++){
		for(int j = 0; j<c; j++){
			printf("%d ", arr[i][j]);
		}
		printf("\n");
	}
}

int main(){
      int arr[][2] = {{1, 2}, {3, 4}};
      int r = 2, c = 2;
	 display(r, c, arr);
}

Output:

1 2
3 4

We can use a single pointer to pass an array as an argument.

Code:

C++ Code

#include <bits/stdc++.h>
using namespace std;
void print(int *nums, int r, int c)
{
	int i, j;
	for (i = 0; i < r; i++)
	{
	for (j = 0; j < c; j++)
	{
	cout<<*((nums+i*c) + j)<<" ";
	}
	cout<<endl; 	
	}
}

int main()
{
	int nums[][3] = {{2, 4, 6}, {8, 10, 12}, {14, 16, 18}};
	int r = 3, c = 3;

	print((int *)nums, r, c);
	return 0;
}

Output:

2 4 6
8 10 12
14 16 18

We know that we can use a pointer that can point towards an array. With this concept, we can pass an array as an argument.

Code:

C++ Code

#include <bits/stdc++.h>

const int m=3;
void display(int (*arr)[m]){
	for(int i = 0; i<m; i++){
		for(int j = 0; j<m; j++)
			std::cout << arr[i][j] << " ";
		std::cout << std::endl;
	}
}

int main(){
	int nums[][3] = {{2, 4, 6}, {8, 10, 12}, {14, 16, 18}};
	display(nums);
}

Output:

2 4 6
8 10 12
14 16 18

Using Double pointers(pointer to pointer)

Code:

C++ Code

#include <bits/stdc++.h>

void display(int **arr, int r, int c){
	for(int i = 0; i<r; i++){
		for(int j = 0; j<c; j++)
			std::cout << arr[i][j] << ' ';
		std::cout << std::endl;
	}
}

int main(){
	int r, c; 
	std::cin >> r >> c;
	
	int** arr = new int*[r];

	for(int i = 0; i<r; i++)
		arr[i] = new int[c];
	
	for(int i = 0; i<r; i++)
		for(int j = 0; j<c; j++)
			std::cin >> arr[i][j];
	
	display(arr, r, c);
}

Special thanks to Asish Kumar for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article