Function returns corrupted Array in C++

Question

I have read some old threads and tested some ideas but my issue still exists so here is what i want: I need a function, what returns a simple array with a fixed size of 181 integer values.

After some tests i have this function:

int *Sonar::scan(int *distances) {
    // Scanning
    for (int i = 0; i <= 180; i++) {
        // Rotates sonar
        //this->rotate(i);
        // Gets the distance
        //distances[i] = this->getDistance();
        distances[i] = i;
    }
    // Returns
    return distances;
}

and call it this way:

            // Sonar
            case 's':
                int distances[181];
                *distances = sonar.scan(distances);
                for (int i = 0; i <= 180; i++) {
                    Serial.println(String(i) + ": " + String(distances[i]));
                }
                break;

But i get this result:

0: 1898
1: 1
2: 2
3: 3
4: 4
...

The value of index 0 is corrupted all the time. So what mistake do i made?

Thank you very much for your help: :-)

Answer 1

The first element of the array is being overwritten with the pointer to the array when you do:

*distances = sonar.scan(distances);

That is because you dereference the array with *distances giving a reference to the first element. You then assign to that with what you return from the scan method (the pointer to the array).

Just doing:

sonar.scan(distances);

would give the result you expect.

There is no need to return from the method as you are passing the array by a form of reference (a pointer) and that means the array is being changed in place.