write.2

Unix操作系统minix 2.0源码

.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)write.2	6.5 (Berkeley) 5/14/86
.\"
.TH WRITE 2 "May 14, 1986"
.UC 4
.SH NAME
write \- write output
.SH SYNOPSIS
.nf
.ft B
#include <sys/types.h>
#include <unistd.h>

ssize_t write(int \fId\fP, const void *\fIbuf\fP, size_t \fInbytes\fP)
.fi
.SH DESCRIPTION
.B Write
attempts to write
.I nbytes
of data to the object referenced by the descriptor
.I d
from the buffer pointed to by
.IR buf .
.PP
On objects capable of seeking, the \fBwrite\fP starts at a position
given by the pointer associated with
.IR d ,
see
.BR lseek (2).
Upon return from
.BR write ,
the pointer is incremented by the number of bytes actually written.
.PP
Objects that are not capable of seeking always write from the current
position.  The value of the pointer associated with such an object
is undefined.
.PP
When using non-blocking I/O on objects such as TCP/IP channels that are
subject to flow control,
.B write
may write fewer bytes than requested;
the return value must be noted,
and the remainder of the operation should be retried when possible.
.SH "RETURN VALUE
Upon successful completion the number of bytes actually written
is returned.  Otherwise a \-1 is returned and the global variable
.B errno
is set to indicate the error.
.SH ERRORS
.B Write
will fail and the file pointer will remain unchanged if one or more
of the following are true:
.TP 15
[EBADF]
\fID\fP is not a valid descriptor open for writing.
.TP 15
[EPIPE]
An attempt is made to write to a pipe that is not open
for reading by any process.
.TP 15
[EPIPE]
An attempt is made to write to a TCP channel
that is not connected to a peer socket.
.TP 15
[EFBIG]
An attempt was made to write a file that exceeds the process's
file size limit or the maximum file size.
.TP 15
[EFAULT]
Part of the data to be written to the file
points outside the process's allocated address space.
.TP 15
[ENOSPC]
There is no free space remaining on the file system
containing the file.
.ig
.TP 15
[EDQUOT]
The user's quota of disk blocks on the file system
containing the file has been exhausted.
..
.TP 15
[EIO]
An I/O error occurred while reading from or writing to the file system.
.TP 15
[EAGAIN]
The file was marked for non-blocking I/O,
and no data could be written immediately.
.SH "SEE ALSO"
.BR fcntl (2),
.BR lseek (2),
.BR open (2),
.BR pipe (2),
.BR read (2).