why doesn't global variables space size isn't affected by changing arrays' size?

Using Arduino Programming Questions
1

Why changing a global array's size or type doesn't change the reported "global variables use" reading in the IDE?
If I change the size of a "int data[600];" global declaration or a declare it as byte I get the same reported space use.

2

You'll have to show the code you're talking about. If you declare that array but don't use it then it may be optimized away.

3

Here's the relevant part of it:

const int dsize=1000;
int data[dsize];

    
void setup() {
  for (int i=0;i<dsize;i++) {data[i]=1;}

Actually 1000 ints should already be too much but I get the same free SRAM size as with dsize=1.

4

Your array is assigned but never used. Probably got optimized out by the compiler.

1 Like
5

Try adding this

 Serial.println(data[0]);

after the for loop

1 Like
6

UKHeliBob:
Try adding this

 Serial.println(data[0]);

after the for loop

This works. Could you explain me why it's necessary for a correct memory usage estimation?

7

Garfielder:
This works. Could you explain me why it's necessary for a correct memory usage estimation?

The estimation was correct. Your code didn't include anything requiring the array to be stored in memory. So, it wasn't.

8

Just because I didn't use the array anywhere?
Well, also this is enough to count the array size in the memory allocation-

int ab=data[3];

or

for (int i=1;i<dsize;i++) {data[i]=data[i-1];}

although I never use elsewhere data[4] or ab itself.
This is a very limited type of optimization.
Thanks. I hope I am getting this right.

9

Garfielder:
Just because I didn't use the array anywhere?

Why should the compiler allocate memory to hold data that's never used?

I don't understand the rest of your question -- if it is a question?

Well, also this is enough to count the array size in the memory allocation-

int ab=data[3];

or

for (int i=1;i<dsize;i++) {data[i]=data[i-1];}

although I never use elsewhere data[4] or ab itself.
This is a very limited type of optimization.
Thanks. I hope I am getting this right.

10

So when the compiler checks a variable for being used it looks for reading its value, or any value from it in case it's an array?