ActiveTcl User Guide

NAME

seek - Change the access position for an open channel

SYNOPSIS

seek channelId offset ?origin?

DESCRIPTION

Changes the current access position for channelId.

ChannelId must be an identifier for an open channel such as a Tcl standard channel (stdin, stdout, or stderr), the return value from an invocation of open or socket, or the result of a channel creation command provided by a Tcl extension.

The offset and origin arguments specify the position at which the next read or write will occur for channelId. Offset must be an integer (which may be negative) and origin must be one of the following:

start

The new access position will be offset bytes from the start of the underlying file or device.

current

The new access position will be offset bytes from the current access position; a negative offset moves the access position backwards in the underlying file or device.

end

The new access position will be offset bytes from the end of the file or device. A negative offset places the access position before the end of file, and a positive offset places the access position after the end of file.

The origin argument defaults to start.

The command flushes all buffered output for the channel before the command returns, even if the channel is in nonblocking mode. It also discards any buffered and unread input. This command returns an empty string. An error occurs if this command is applied to channels whose underlying file or device does not support seeking.

Note that offset values are byte offsets, not character offsets. Both seek and tell operate in terms of bytes, not characters, unlike read.

SEE ALSO

file, open, close, gets, tell, Tcl_StandardChannels

KEYWORDS

access position, file, seek

Copyright © 1993 The Regents of the University of California.
Copyright © 1994-1996 Sun Microsystems, Inc.
Copyright © 1995-1997 Roger E. Critchlow Jr.