How to make passing an array by reference optional in C++ function?

June 18, 2023

Is there a way to pass default value to array which is passed by reference to a function so that passing it is not necessary?

I have a function like this:

void foo(int (&arr) [3])
{
    //some code...
}

Then i tried this:

void foo(int (&arr) [3] = nullptr)
{
    //some code...
}

but it obvoiusly didn’t work because reference cannot be nullptr and it is not even an array.

EDIT:
I would like not to use std::array if possible, and I also need to know the size of passed array without passing its size which is why I didn’t do this: int (*arr)[3].

>Solution :

In C++, you cannot directly pass a default value to an array passed by reference. However, you can achieve a similar effect by overloading the function with a version that accepts a default array and calls the original function with it.

Here is a Code

void foo(int (&arr)[3]){}

void foo()
{
    int defaultArr[3] = {1, 2, 3};
    foo(defaultArr);
}
int main()
{
    int arr[3] = {2, 1, 4};
    foo(arr); 

    foo();     
    return 0;
}