get previous offset in a structure id - structure type ID offset - current offset returns: -1 if bad structure type ID is passed or no (more) offsets in the structure otherwise returns previous offset in a structure. NOTE: IDA allows 'holes' between members of a structure. It treats these 'holes' as unnamed arrays of bytes. This function returns a member offset or a hole offset. It will return size of the structure if input 'offset' is bigger than the structure size. NOTE: Union members are, in IDA's internals, located at subsequent byte offsets: member 0 -> offset 0x0, member 1 -> offset 0x1, etc...long get_prev_offset(long id, long offset);