seek.2

UNIX v6源代码 这几乎是最经典的unix版本 unix操作系统设计和莱昂氏unix源代码分析都是用的该版

.th SEEK II 8/5/73
.sh NAME
seek \*- move read/write pointer
.sh SYNOPSIS
(seek = 19.)
.br
(file descriptor in r0)
.ft B
.br
sys seek; offset; ptrname
.s3
seek(fildes, offset, ptrname)
.ft R
.sh DESCRIPTION
The file
descriptor refers to a file open for reading or writing.
The read (resp. write) pointer for the file is set as follows:
.s3
.lp +6 3
if
.it ptrname
is 0, the pointer is set to
.it offset.
.s3
.lp +6 3
if
.it ptrname
is 1, the pointer is set to its current location plus
.it offset.
.s3
.lp +6 3
if
.it ptrname
is 2, the pointer is set to the size of the
file plus
.it offset.
.s3
.lp +6 3
if
.it ptrname
is 3, 4 or 5,
the meaning is as above for
0, 1 and 2 except that
the offset is
multiplied by 512.
.s3
.i0
If
.it ptrname
is 0 or 3,
.it offset
is unsigned,
otherwise
it is signed.
.sh "SEE ALSO"
open (II), creat (II)
.sh DIAGNOSTICS
The error bit
(c-bit) is set for an undefined file descriptor.
From C, a \*-1 return indicates an error.