Passing Array List pointer to function

[chozokennedy]

I'm going to pass my array pointer to the function parameter. I'm quite not sure how to use pointer as array list. Here my current codes...

void FunctionA(int arr_merge[])
{
    int SizeArray = sizeof(arr_merge)/sizeof(arr_merge[0]);
    cout << SizeArray << endl; //Output 0 instead of 9
    int BeginIndex = 0;
    int LastIndex = arr_merge[SizeArray-1];
    int mid = floor(BeginIndex+LastIndex/2);
}

int main (void)
{
    int arrayNumber[] = {1,2,3,4,5,6,7,8,9};
    FunctionA(arrayNumber);
    return 0;
}

[Cody0023]

To assign the variable LastIndex to the last element of the array,arr_merge[SizeArray] is enough. Subtracting one from the subscript gives the second to last element.

To find the middle of an array you need parenthesis.

((BeginIndex+LastIndex)/2)

Not sure why thats a parameter when it can just be assigned to mid though.

Arrays are implicitly passed as pointers automatically...I think that's what you were trying to know....

[z05DSL3A]

In reality void FunctionA(int arr_merge[]) is void FunctionA(int * arr_merge). So inside the function you have no information about the size of the array, so SizeArray is being calculated as the size of a pointer divided by the size of an int (I would expect that to be one but anyway).

// either pass in the size...
void FunctionA(int arr_merge[], int N)
{
    int SizeArray = N;
    cout << SizeArray << endl; 
}

//or pass the array by reference, and use templates
template <typename T, int N>
void FunctionB(T (&arr_merge) [N])
{
    int SizeArray = N;
    cout << SizeArray << endl; 
}


int main()
{
    int arrayNumber[] = {1,2,3,4,5,6,7,8,9};
    
    // pass in the size
    int size = (sizeof(arrayNumber)/sizeof(arrayNumber[0]));
    
    FunctionA(arrayNumber, size);
    
    // pass the array by reference...
    FunctionB(arrayNumber);

    return 0;
}