为什么函数只使用数组的第一个元素？ （C ++）

Question

I was trying to figure out a QuickSort algorithm. But, it looks like I can't pass the array into Partition and QuickSort function. They only process the first element of the array.

How can I fix it?

template < class T > int getArrayLen(T & array) {
    return (sizeof(array) / sizeof(array[0]));
}

int Partition(int a[], int first, int last) {
    int pivot = a[last];
    int i = first - 1;
    for (int j = first; j < last; j++) {
        if (a[j] <= pivot) {
            i++;
            swap(a[i], a[j]);
        }
    }
    swap(a[i + 1], a[last]);
    return i + 1;
}

void QuickSort(int a[], int first, int last) {
    int pivot;

    if (first < last) {
        pivot = Partition(a, first, last);
        QuickSort(a, first, pivot);
        QuickSort(a, pivot + 1, last);
    }
 }

 int main() {
    int a[] = {
         4, 32, 3, 13, 48, 45, 12, 54, 7, 42, 3, 12, 5, 24, 20
    };
    int length = getArrayLen(a);
    QuickSort(a, 0, length - 1);
}

Answer 1

Just decrease one from pivot before calling QuickSort again:

void QuickSort(int a[], int first, int last)
{
    int pivot;

    if (first < last)
    {
        pivot = Partition(a, first, last);
        QuickSort(a, first, pivot - 1);  // <--  HERE
        QuickSort(a, pivot + 1, last);
    }
}

And every thing is OK. Also test for various sizes of a : 1, 2, 3, 4, 5, ...