| isfd | isam file descriptor |
| data | pointer to data buffer to be loaded |
| recnum | an existing active record number |
ISTRUE, or ISFALSE, in which case the error code is returned by isErrno, or found in isfd->iserrno
isData performs a direct read on the data file, and does not disturb the current index pointer, and does not check for record locks. it will return ENOREC if the record requested does not exist or has been deleted.
isData is provided primarily as a means of accessing data records in as an efficient a manner as possible.