2D C-Style Arrays

2D C-style arrays in C++ are essentially arrays of arrays. Each element in a 2D array is itself a 1D array.

Here's how you can create and work with 2D C-style arrays:

Declaration and Initialization

The following example demonstrates how we can create a 2D C-style array, and optionally provide it with initial values:

1// Declare a 3x3 int array
2int arr[3][3];
3
4// Initialize with values
5int arr[3][3] = {
6    {1, 2, 3},
7    {4, 5, 6},
8    {7, 8, 9}
9};

Accessing Elements

Here, we show how to access and modify elements in a 2D C-style array:

1// Access individual elements
2// Accessing row 1, column 2
3int val = arr[1][2];
4
5// Modify an element
6// Modifying row 0, column 0
7arr[0][0] = 10;

Passing to Functions

We can pass a 2D C-style array to a function in the usual way:

1#include <iostream>
2
3void print2DArray(int arr[][3], int rows) {
4  for (int i = 0; i < rows; ++i) {
5    for (int j = 0; j < 3; ++j) {
6      std::cout << arr[i][j] << ' ';
7    }
8    std::cout << '\n';
9  }
10}
11
12int main() {
13  int arr[2][3] = {{1, 2, 3}, {4, 5, 6}};
14  print2DArray(arr, 2);
15}

11 2 3
24 5 6

Note that when passing a 2D array to a function, you must specify all dimensions except the first one.

Flattening

2D arrays are laid out contiguously in memory, so you can also treat them as a 1D array:

1int arr[2][3] = {{1, 2, 3}, {4, 5, 6}};
2
3// Treat as 1D array
4for (int i = 0; i < 6; ++i) {
5    std::cout << *(*arr + i) << ' ';
6}

However, for more complex and dynamic 2D arrays, consider using a std::vector<std::vector<int>> instead. It offers more flexibility and convenience at the cost of some performance overhead.

Understanding how to work with 2D C-style arrays is important for certain applications and for understanding how arrays are laid out in memory, but in modern C++, 2D std::vectors or other library containers are often preferred for their safety and ease of use.