How to Pass 2D Array to Function in C++: Syntax and Examples

In C++, you can pass a 2D array to a function by specifying the array parameter with fixed column size, like void func(int arr[][COLS]). Alternatively, you can use pointers or templates for more flexibility. The key is to fix the number of columns so the compiler knows the memory layout.

Syntax

To pass a 2D array to a function, you must specify the number of columns so the compiler knows how to access elements. The syntax looks like this:

• void functionName(type arrayName[][COLS]) - where COLS is the fixed number of columns.
• You can also use pointer notation: void functionName(type (*arrayName)[COLS]).
• The number of rows can be left unspecified because it is not needed for pointer arithmetic.

cpp

void printArray(int arr[][3], int rows) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < 3; j++) {
            std::cout << arr[i][j] << ' ';
        }
        std::cout << '\n';
    }
}

Example

This example shows how to declare a 2D array, pass it to a function, and print its elements. The function receives the array and the number of rows.

cpp

#include <iostream>

void printArray(int arr[][3], int rows) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < 3; j++) {
            std::cout << arr[i][j] << ' ';
        }
        std::cout << '\n';
    }
}

int main() {
    int myArray[2][3] = {{1, 2, 3}, {4, 5, 6}};
    printArray(myArray, 2);
    return 0;
}

Output

1 2 3 
4 5 6 

Common Pitfalls

Common mistakes when passing 2D arrays include:

• Not specifying the number of columns in the function parameter, which causes a compilation error.
• Confusing rows and columns sizes.
• Trying to pass a 2D array without fixing the column size or using pointers.

Example of wrong and right ways:

cpp

// Wrong: missing column size
// void printArray(int arr[][], int rows) { } // Error

// Right: fixed column size
void printArray(int arr[][3], int rows) { /*...*/ }

Quick Reference

Method	Syntax	Notes
Fixed column size	void func(int arr[][COLS])	Most common, simple to use
Pointer to array	void func(int (*arr)[COLS])	Equivalent to fixed column size syntax
Using templates	template void func(int (&arr)[R][C])	Flexible, works with any size
Using double pointer	void func(int** arr)	Not for true 2D arrays, needs dynamic allocation

Key Takeaways

Always specify the number of columns when passing a 2D array to a function in C++.

You can pass 2D arrays using fixed-size arrays, pointers, or templates for flexibility.

Not specifying column size causes compilation errors.

Passing a double pointer is not the same as passing a 2D array and requires dynamic memory.

Templates allow writing functions that accept any 2D array size without hardcoding dimensions.