IDA Help: Data representation: structure offset

Syntax:
  __stroff(structname)
  __stroff(structname, delta)

Instead of a plain number, the name of a struct or union member will be used.
If delta is present, it will be subtracted from the value before converting
it into a struct/union member name.

Example:
  An integer variable named `var` that hold an offset from the beginning of
  the `mystruct` structure:

  int var __stroff(mystruct);

  If mystruct is defined like this:

  struct mystruct
  {
    char a;
    char b;
    char c;
    char d;
  }

  The value 2 will be represented as `mystruct.c`

Another example:
  A structure offset with a delta:

  int var __stroff(mystruct, 1);

  The value 2 will be represented as `mystruct.d-1`