83 lines
2 KiB
Groff
83 lines
2 KiB
Groff
.\" Copyright (c) 1980 Regents of the University of California.
|
|
.\" All rights reserved. The Berkeley software License Agreement
|
|
.\" specifies the terms and conditions for redistribution.
|
|
.\"
|
|
.\" @(#)read.2 6.6 (Berkeley) 5/23/86
|
|
.\"
|
|
.TH READ 2 "May 23, 1986"
|
|
.UC 4
|
|
.SH NAME
|
|
read \- read input
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.ft B
|
|
#include <sys/types.h>
|
|
#include <unistd.h>
|
|
|
|
ssize_t read(int \fId\fP, void *\fIbuf\fP, size_t \fInbytes\fP)
|
|
.fi
|
|
.SH DESCRIPTION
|
|
.B Read
|
|
attempts to read
|
|
.I nbytes
|
|
of data from the object referenced by the descriptor
|
|
.I d
|
|
into the buffer pointed to by
|
|
.IR buf .
|
|
.PP
|
|
On objects capable of seeking, the
|
|
.B read
|
|
starts at a position
|
|
given by the pointer associated with
|
|
.IR d
|
|
(see
|
|
.BR lseek (2)).
|
|
Upon return from
|
|
.BR read ,
|
|
the pointer is incremented by the number of bytes actually read.
|
|
.PP
|
|
Objects that are not capable of seeking always read from the current
|
|
position. The value of the pointer associated with such an
|
|
object is undefined.
|
|
.PP
|
|
Upon successful completion,
|
|
.B read
|
|
return the number of bytes actually read and placed in the buffer.
|
|
The system guarantees to read the number of bytes requested if
|
|
the descriptor references a normal file that has that many bytes left
|
|
before the end-of-file, but in no other case.
|
|
.PP
|
|
If the returned value is 0, then
|
|
end-of-file has been reached.
|
|
.SH "RETURN VALUE
|
|
If successful, the
|
|
number of bytes actually read is returned.
|
|
Otherwise, a \-1 is returned and the global variable
|
|
.B errno
|
|
is set to indicate the error.
|
|
.SH "ERRORS
|
|
.B Read
|
|
will fail if one or more of the following are true:
|
|
.TP 15
|
|
[EBADF]
|
|
\fID\fP is not a valid descriptor open for reading.
|
|
.TP 15
|
|
[EFAULT]
|
|
\fIBuf\fP points outside the allocated address space.
|
|
.TP 15
|
|
[EIO]
|
|
An I/O error occurred while reading from the file system.
|
|
.TP 15
|
|
[EINTR]
|
|
A read from a slow device was interrupted before
|
|
any data arrived by the delivery of a signal.
|
|
.TP 15
|
|
[EAGAIN]
|
|
The file was marked for non-blocking I/O,
|
|
and no data were ready to be read.
|
|
.SH "SEE ALSO"
|
|
.BR dup (2),
|
|
.BR fcntl (2),
|
|
.BR open (2),
|
|
.BR pipe (2),
|
|
.BR write (2).
|