offset meaning

[srscode]

I'm reading an e-book about C++ and found something i didn't understand.

When speaking of something like this:

  char* ptr = &charArray[0];

What does an offset mean? or an integer offset?
or what does an offset mean in general in programming?

[YokoTsuno]

An offset generally refers to a value that is added to another base value, usually a (base) pointer in order to access a single element in a sequential list of elements, usually an array.


Example:
- In your case ptr points to the 1st element of the array or charArray[0],
*ptr is therefore the value stored in charArray[0];
- If you'd like to address the 5th element you can add an OFFSET to ptr like
ptr = ptr + 4; Now *ptr is the value of the 5th element or charArray[4];

[srscode]

So is &charArray[4] also an offset? or only

ptr = ptr + 4;

?

[YokoTsuno]

"So is &charArray[4] also an offset? or only"
No this is generally not understood as an offset but a base address that refers to the 5th element.

I should have chosen a base pointer instead of adding the offset to the original pointer. I hope this is clearer

char* baseptr = &charArray[0];
char* ptr;

ptr =  baseptr + 4; //Offset is 4
ptr =  baseptr + 2; //Offset is 2
      

[srscode]

So whatever number you write in the brackets are the offset? or in other words the offset is the element you choose in the array (by number aka offset)?
Did i get it right?

[YokoTsuno]

no you still misunderstand.

The 4 in &charArray[4] is an INDEX.
The 4 in (ptr = baseptr + 4) is an OFFSET

Both might have the same outcome but they are not the same in terms of definition.

[srscode]

I think i get it now, thanks :)