Positions the file pointer to a user-defined
offset in a text file. This statement does not require you to close
and reopen the file.
Syntax
SEEK
{ INPUT | OUTPUT | STREAM stream | STREAM-HANDLE handle}
TO {expression| END }
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- INPUT
- If you specify INPUT, the SEEK statement positions the file
pointer in the unnamed input stream.
- OUTPUT
- If you specify OUTPUT, the SEEK statement positions the file pointer
in the unnamed output stream.
- STREAM stream
- If you specify STREAM stream, the SEEK statement
positions the file pointer in the named input or output stream. If
you do not name a stream, the AVM uses the unnamed stream.
- STREAM-HANDLE handle
- If you specify the handle to a stream, the SEEK statement returns
the current position of the file pointer in the stream. If handle it
is not a valid handle to a stream, the AVM generates a run-time
error.
- TO expression
- An expression whose value is INT64 that indicates the byte location to
position the file pointer. If expression equals
0, the file pointer is positioned to the first byte in the file.
If you want to position the pointer to the last byte in the file,
but you do not know the offset, use END.
- END
- Positions the pointer to the last byte in the file.
Example
Since
text file formats differ on each machine, the SEEK function does
not necessarily return a number that is meaningful to anyone, but
it is meaningful to the SEEK statement. With the exception of SEEK
to 0 or SEEK TO END, any address used in the SEEK statement is only
guaranteed to behave consistently if the address was previously
derived from the SEEK function. Therefore, an expression such as
SEEK TO SEEK (INPUT) -n might work differently on different operating
systems. Record delimiters must be new-lines on UNIX, and carriage-return/linefeed
pairs on all others.
r-seek.p
/* This procedure seeks to the end-of-file, collects the seek address, and
writes a record. The record is subsequently retrieved using the SEEK
statement on the stashed seek address. */
DEFINE VARIABLE savepos AS INT64 NO-UNDO.
DEFINE VARIABLE c AS CHARACTER NO-UNDO FORMAT "x(20)".
OUTPUT TO seek.out APPEND NO-ECHO.
savepos = SEEK(OUTPUT).
PUT UNFORMATTED "abcdefg" SKIP.
OUTPUT CLOSE.
INPUT FROM seek.out NO-ECHO.
SEEK INPUT TO savepos.
SET c.
DISPLAY c.
INPUT CLOSE.
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Notes
- The
SEEK statement does not work with named streams identified in the
INPUT-THROUGH, OUTPUT-THROUGH, or INPUT-OUTPUT-THROUGH statements.
- An expression such as SEEK TO SEEK (INPUT) -n might work differently
on different operating systems.
- For more information on streams, see the chapter on alternate
I/O sources in OpenEdge Development: Programming Interfaces.
