IO::Seekable
Section: Perl Programmers Reference Guide (3perl)
Updated: 2019-04-20
Page Index
NAME
IO::Seekable - supply seek based methods for I/O objects
SYNOPSIS
use IO::Seekable;
package IO::Something;
@ISA = qw(IO::Seekable);
DESCRIPTION
"IO::Seekable" does not have a constructor of its own as it is intended to
be inherited by other
"IO::Handle" based objects. It provides methods
which allow seeking of the file descriptors.
- $io->getpos
-
Returns an opaque value that represents the current position of the
IO::File, or "undef" if this is not possible (eg an unseekable stream such
as a terminal, pipe or socket). If the fgetpos() function is available in
your C library it is used to implements getpos, else perl emulates getpos
using C's ftell() function.
- $io->setpos
-
Uses the value of a previous getpos call to return to a previously visited
position. Returns ``0 but true'' on success, "undef" on failure.
See perlfunc for complete descriptions of each of the following
supported "IO::Seekable" methods, which are just front ends for the
corresponding built-in functions:
- $io->seek ( POS, WHENCE )
-
Seek the IO::File to position POS, relative to WHENCE:
-
- WHENCE=0 (SEEK_SET)
-
POS is absolute position. (Seek relative to the start of the file)
- WHENCE=1 (SEEK_CUR)
-
POS is an offset from the current position. (Seek relative to current)
- WHENCE=2 (SEEK_END)
-
POS is an offset from the end of the file. (Seek relative to end)
-
The SEEK_* constants can be imported from the "Fcntl" module if you
don't wish to use the numbers 0 1 or 2 in your code.
Returns 1 upon success, 0 otherwise.
- $io->sysseek( POS, WHENCE )
-
Similar to $io->seek, but sets the IO::File's position using the system
call lseek(2) directly, so will confuse most perl IO operators except
sysread and syswrite (see perlfunc for full details)
Returns the new position, or "undef" on failure. A position
of zero is returned as the string "0 but true"
- $io->tell
-
Returns the IO::File's current position, or -1 on error.
SEE ALSO
perlfunc,
``I/O Operators'' in perlop,
IO::Handle
IO::File
HISTORY
Derived from FileHandle.pm by Graham Barr <
gbarr@pobox.com>