SEEK statement

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.


SEEK { INPUT \| OUTPUT \| STREAM `stream` \| STREAM-HANDLE `handle` } TO { `expression` \| END }

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.

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.

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.

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.

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.