fseek.3s

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3S 代码 · 共 76 行

.\" SCCSID: @(#)fseek.3s	8.1	9/11/90
.TH fseek 3s
.SH Name
fseek, ftell, rewind \- reposition a file pointer in a stream
.SH Syntax
.B #include <stdio.h>
.PP
.B int fseek(\fIstream, offset, ptrname\fP)
.br
.SM
.B FILE
.B *\fIstream\fP;
.br
.B long \fIoffset\fP;
.br
.B int \fIptrname\fP;
.PP
.B long ftell(\fIstream\fP)
.br
.SM
.B FILE
.B *\fIstream\fP;
.PP
.B void rewind(\fIstream\fP)
.br
.SM
.B FILE
.B *\fIstream\fP;
.SH Description
.NXR "fseek subroutine (standard I/O)"
.NXR "ftell subroutine (standard I/O)"
.NXR "rewind subroutine"
.NXR "stream" "repositioning"
The
.PN fseek
function sets the position of the next input or output
operation on the
.IR stream .
The new position is at the signed distance
.I offset
bytes
from the beginning, the current position, or the end of the file,
according as 
.I ptrname
has the value SEEK_SET, SEEK_CUR, or SEEK_END.
.PP
The
.PN fseek
function undoes any effects of
.MS ungetc 3s .
.PP
The
.PN ftell
function returns the current value of the 
offset relative to the beginning
of the file associated with the named
.IR stream .
It is measured in bytes and is the only foolproof way to obtain
an
.I offset
for
.PN fseek .
.PP
The
.PN rewind 
(stream)
function is equivalent to
.PN fseek 
(stream , 0L, 0, SEEK_SET), except that no value is returned.
.SH Return Values
The
.PN fseek
function returns \-1 for improper seeks, otherwise 0.
.SH See Also
lseek(2), fopen(3s)