io::seekable.3

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.\" ========================================================================
.\"
.IX Title "IO::Seekable 3"
.TH IO::Seekable 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
IO::Seekable \- supply seek based methods for I/O objects
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&    use IO::Seekable;
\&    package IO::Something;
\&    @ISA = qw(IO::Seekable);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`IO::Seekable\*(C'\fR does not have a constructor of its own as it is intended to
be inherited by other \f(CW\*(C`IO::Handle\*(C'\fR based objects. It provides methods
which allow seeking of the file descriptors.
.ie n .IP "$io\->getpos" 4
.el .IP "\f(CW$io\fR\->getpos" 4
.IX Item "$io->getpos"
Returns an opaque value that represents the current position of the
IO::File, or \f(CW\*(C`undef\*(C'\fR if this is not possible (eg an unseekable stream such
as a terminal, pipe or socket). If the \fIfgetpos()\fR function is available in
your C library it is used to implements getpos, else perl emulates getpos
using C's \fIftell()\fR function.
.ie n .IP "$io\->setpos" 4
.el .IP "\f(CW$io\fR\->setpos" 4
.IX Item "$io->setpos"
Uses the value of a previous getpos call to return to a previously visited
position. Returns \*(L"0 but true\*(R" on success, \f(CW\*(C`undef\*(C'\fR on failure.
.PP
See perlfunc for complete descriptions of each of the following
supported \f(CW\*(C`IO::Seekable\*(C'\fR methods, which are just front ends for the
corresponding built-in functions:
.ie n .IP "$io\->seek ( \s-1POS\s0, \s-1WHENCE\s0 )" 4
.el .IP "\f(CW$io\fR\->seek ( \s-1POS\s0, \s-1WHENCE\s0 )" 4
.IX Item "$io->seek ( POS, WHENCE )"
Seek the IO::File to position \s-1POS\s0, relative to \s-1WHENCE:\s0
.RS 4
.IP "WHENCE=0 (\s-1SEEK_SET\s0)" 8
.IX Item "WHENCE=0 (SEEK_SET)"
\&\s-1POS\s0 is absolute position. (Seek relative to the start of the file)
.IP "WHENCE=1 (\s-1SEEK_CUR\s0)" 8
.IX Item "WHENCE=1 (SEEK_CUR)"
\&\s-1POS\s0 is an offset from the current position. (Seek relative to current)
.IP "WHENCE=2 (\s-1SEEK_END\s0)" 8
.IX Item "WHENCE=2 (SEEK_END)"
\&\s-1POS\s0 is an offset from the end of the file. (Seek relative to end)
.RE
.RS 4
.Sp
The SEEK_* constants can be imported from the \f(CW\*(C`Fcntl\*(C'\fR module if you
don't wish to use the numbers \f(CW0\fR \f(CW1\fR or \f(CW2\fR in your code.
.Sp
Returns \f(CW1\fR upon success, \f(CW0\fR otherwise.
.RE
.ie n .IP "$io\->sysseek( \s-1POS\s0, \s-1WHENCE\s0 )" 4
.el .IP "\f(CW$io\fR\->sysseek( \s-1POS\s0, \s-1WHENCE\s0 )" 4
.IX Item "$io->sysseek( POS, WHENCE )"
Similar to \f(CW$io\fR\->seek, but sets the IO::File's position using the system
call \fIlseek\fR\|(2) directly, so will confuse most perl \s-1IO\s0 operators except
sysread and syswrite (see perlfunc for full details)
.Sp
Returns the new position, or \f(CW\*(C`undef\*(C'\fR on failure.  A position
of zero is returned as the string \f(CW"0 but true"\fR
.ie n .IP "$io\->tell" 4
.el .IP "\f(CW$io\fR\->tell" 4
.IX Item "$io->tell"
Returns the IO::File's current position, or \-1 on error.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perlfunc, 
\&\*(L"I/O Operators\*(R" in perlop,
IO::Handle
IO::File
.SH "HISTORY"
.IX Header "HISTORY"
Derived from FileHandle.pm by Graham Barr <[e-mail]>