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Perl Cookbook
book

Perl Cookbook

by Tom Christiansen, Nathan Torkington
August 1998
Intermediate to advanced content levelIntermediate to advanced
800 pages
39h 20m
English
O'Reilly Media, Inc.
Content preview from Perl Cookbook

Using Random-Access I/O

Problem

You have to read a binary record from the middle of a large file but don’t want to read a record at a time to get there.

Solution

Once you know the record’s size, multiply it by the record number to get the byte address, and then seek to that byte address and read the record:

$ADDRESS = $RECSIZE * $RECNO;
seek(FH, $ADDRESS, 0) or die "seek:$!";
read(FH, $BUFFER, $RECSIZE);

Discussion

The Solution assumes the first record has a RECNO of 0. If you’re counting from one, use:

$ADDRESS = $RECSIZE * ($RECNO-1);

This won’t work on a text file unless all lines are the same length. This is rarely the case.

See Also

The seek function in perlfunc (1) and in Chapter 3 of Programming Perl ; Section 8.13

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Publisher Resources

ISBN: 1565922433Supplemental ContentCatalog PageErrata