1#
2
3package IO::Seekable;
4
5=head1 NAME
6
7IO::Seekable - supply seek based methods for I/O objects
8
9=head1 SYNOPSIS
10
11    use IO::Seekable;
12    package IO::Something;
13    @ISA = qw(IO::Seekable);
14
15=head1 DESCRIPTION
16
17C<IO::Seekable> does not have a constructor of its own as it is intended to
18be inherited by other C<IO::Handle> based objects. It provides methods
19which allow seeking of the file descriptors.
20
21=over 4
22
23=item $io->getpos
24
25Returns an opaque value that represents the current position of the
26IO::File, or C<undef> if this is not possible (eg an unseekable stream such
27as a terminal, pipe or socket). If the fgetpos() function is available in
28your C library it is used to implements getpos, else perl emulates getpos
29using C's ftell() function.
30
31=item $io->setpos
32
33Uses the value of a previous getpos call to return to a previously visited
34position. Returns "0 but true" on success, C<undef> on failure.
35
36=back
37
38See L<perlfunc> for complete descriptions of each of the following
39supported C<IO::Seekable> methods, which are just front ends for the
40corresponding built-in functions:
41
42=over 4
43
44=item $io->seek ( POS, WHENCE )
45
46Seek the IO::File to position POS, relative to WHENCE:
47
48=over 8
49
50=item WHENCE=0 (SEEK_SET)
51
52POS is absolute position. (Seek relative to the start of the file)
53
54=item WHENCE=1 (SEEK_CUR)
55
56POS is an offset from the current position. (Seek relative to current)
57
58=item WHENCE=2 (SEEK_END)
59
60POS is an offset from the end of the file. (Seek relative to end)
61
62=back
63
64The SEEK_* constants can be imported from the C<Fcntl> module if you
65don't wish to use the numbers C<0> C<1> or C<2> in your code.
66
67Returns C<1> upon success, C<0> otherwise.
68
69=item $io->sysseek( POS, WHENCE )
70
71Similar to $io->seek, but sets the IO::File's position using the system
72call lseek(2) directly, so will confuse most perl IO operators except
73sysread and syswrite (see L<perlfunc> for full details)
74
75Returns the new position, or C<undef> on failure.  A position
76of zero is returned as the string C<"0 but true">
77
78=item $io->tell
79
80Returns the IO::File's current position, or -1 on error.
81
82=back
83
84=head1 SEE ALSO
85
86L<perlfunc>,
87L<perlop/"I/O Operators">,
88L<IO::Handle>
89L<IO::File>
90
91=head1 HISTORY
92
93Derived from FileHandle.pm by Graham Barr E<lt>gbarr@pobox.comE<gt>
94
95=cut
96
97use 5.008_001;
98use Carp;
99use strict;
100use IO::Handle ();
101# XXX we can't get these from IO::Handle or we'll get prototype
102# mismatch warnings on C<use POSIX; use IO::File;> :-(
103use Fcntl qw(SEEK_SET SEEK_CUR SEEK_END);
104require Exporter;
105
106our @EXPORT = qw(SEEK_SET SEEK_CUR SEEK_END);
107our @ISA = qw(Exporter);
108
109our $VERSION = "1.52";
110
111sub seek {
112    @_ == 3 or croak 'usage: $io->seek(POS, WHENCE)';
113    seek($_[0], $_[1], $_[2]);
114}
115
116sub sysseek {
117    @_ == 3 or croak 'usage: $io->sysseek(POS, WHENCE)';
118    sysseek($_[0], $_[1], $_[2]);
119}
120
121sub tell {
122    @_ == 1 or croak 'usage: $io->tell()';
123    tell($_[0]);
124}
125
1261;
127