Converts from a pointer to position within a string to an integer character offset.
Since 2.10, this function allows pos to be before str, and returns a negative offset in this case.
a UTF-8 encoded string
a pointer to a position within str
the resulting character offset
Converts from a pointer to position within a string to an integer character offset.
Since 2.10, this function allows pos to be before str, and returns a negative offset in this case.