c++ arrays 上的 output 错误

Question

I am fairly new to C++ so this question may seem very basic(dumb.), I am trying to return an array of (int i. int j) which is a position(coordinates).

Here is my code:

int* Unblocker(int d1[2],int d2[2])
{
int unblocker_position[2];
int distance;
distance = abs(d1[0]-d2[0])+ abs(d1[1]-d2[1]);
switch (distance)
{
case 1:
    break;
case 2:
    switch (abs(d1[0] - d2[0]))
    {
    case 2:
        unblocker_position[0] = 1;
        unblocker_position[1] = 0;
        return unblocker_position;
        break;
    default:
        return NULL;
        break;
    }
    break;
default:
    return NULL;
    break;
}
}

int main(){
   int p1[2]={0,0};
   int p2[2]={2,0};
   int * a = Unblocker(p1,p2);
   cout << a[0] << " " << a[1] << endl;
   return 0;}

The output is:

  1 1 

however, I expect "1 0". I am not sure if I made a mistake using a switch or in using an array as the return type. I removed other cases in the switch to make it easier to get to the point.

Answer 1

If you want to return a pointer to a local variable you need to store the variable in the heap. To do so you have to use the new operator.

int *Unblocker(int d1[2], int d2[2])
{
    int *unblocker_position = new int[2];
    int distance;
    distance = abs(d1[0] - d2[0]) + abs(d1[1] - d2[1]);
    switch (distance)
    {
    case 1:
        break;
    case 2:
        switch (abs(d1[0] - d2[0]))
        {
        case 2:
            unblocker_position[0] = 1;
            unblocker_position[1] = 0;
            return unblocker_position;
            break;
        default:
            return NULL;
            break;
        }
        break;
    default:
        return NULL;
        break;
    }
    return NULL;
}

int main()
{
    int p1[2] = {0, 0};
    int p2[2] = {2, 0};
    int *a = Unblocker(p1, p2);
    cout << a[0] << " " << a[1] << endl;
    delete a;
    return 0;
}

Remember to use the delete operator to prevent memory leaks.

If you want to learn more about this topic I suggest you look at smart pointers .