Getting strange output from function when adding digitalRead()

Projects Programming
1

Hi

I've a larger project where I'm using a function to return an array for later use. First I got strange returnvalues from the function, like 512 instead of 0 or 1. When I commented almost all code in the function it worked.

I've broken it down to this, and it seems to be when adding digitalRead the problem begins.

int* arr0[13];
const int buttonPin=3;
int buttonState=0;

void setup(){
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}

// the loop routine runs over and over again forever:
void loop(){
  arr0[0]=myFunction(5,7,buttonPin);
  Serial.println(arr0[0][1]);
}

int* myFunction(int var0, int var1, int var2){
  buttonState=digitalRead(buttonPin);
  int arr1[3];
  arr1[0]=var0;
  arr1[1]=var1;
  arr1[2]=var2;
  return arr1;
}

I see the code as follow:
I define an array named arr0 with length 13

I call the function with myFunction(5, 7, buttonPin) and save returnvalue at index 0 in array arr0
I want to print out number 7 that I've passed to myFunction. It should be placed at arr0[0][1]?
buttonPin is 3 as stated earlier in code
I then define a array named arr1 with length 3
index 0 is filled with 5
index 1 is filled with 7
and index 2 is filled with buttonPin (3)
arr1 is returned

Why am I not getting the value that I'm looking for?

Best Regards
Niclas

2

I've a larger project where I'm using a function to return an array for later use.

Then, it is not written in C or C++ for the Arduino. Functions can not return arrays.

I define an array named arr0 with length 13

That is an array of pointers. They are all initialized to NULL.

  int arr1[3];

This is a local array, on the heap.

}

It goes away here, but

  return arr1;

Here, you've returned a pointer to that memory location.

  Serial.println(arr0[0][1]);

And here you try to dereference that pointer that now points to garbage.

You need to pass the function an array to populate. That array needs to be statically defined.

3

Code:

int arr1[3];

This is a local array, on the heap.

For "heap" read "stack".