This routine changes the current position of the file for subsequent READs.
The only time the runtime supports a seek in a sequential file is 1) to find the last record in order to read the file backwards, and 2) after each READ to seek to the previous record. These are the only uses of SEEK supported by this library. The file must be locked to ensure that other users of the file don't add to it.
S-SEEK-FUNCTION has three parameters: f, offset and mode.
| f | must be a valid file handle returned by OPEN. |
| offset | is the number of bytes to move from the current file position. Offset is limited to a 32-bit value. |
| mode | is a flag that specifies the position from which the offset is measured. A value of zero sets the position at the beginning of the file, regardless of the current position. A value of one sets the position to the current position. A value of two sets the position to the end of the file. Note that offset can be negative value. |