Name
write — write to a file descriptor
Synopsis
#include <unistd.h>
ssize_t write( |
int |
fd, |
| |
const void * |
buf, |
| |
size_t |
count); |
DESCRIPTION
write() writes up to
count bytes to the
file referenced by the file descriptor fd from the buffer starting at
buf. POSIX requires
that a read(2) which can be proved
to occur after a write() has
returned returns the new data. Note that not all file systems
are POSIX conforming.
RETURN VALUE
On success, the number of bytes written are returned (zero
indicates nothing was written). On error, −1 is
returned, and errno is set
appropriately.
If count is zero
and fd refers to a
regular file, then write
() may return a failure status if one of the
errors below is detected. If no errors are detected, 0 will
be returned without causing any other effect. If count is zero and fd refers to a file other than
a regular file, the results are not specified.
ERRORS
- EAGAIN
-
Non-blocking I/O has been selected using
O_NONBLOCK and the write
would block.
- EBADF
-
fd is not a
valid file descriptor or is not open for writing.
- EFAULT
-
buf is
outside your accessible address space.
- EFBIG
-
An attempt was made to write a file that exceeds the
implementation-defined maximum file size or the
process' file size limit, or to write at a position
past the maximum allowed offset.
- EINTR
-
The call was interrupted by a signal before any data
was written.
- EINVAL
-
fd is
attached to an object which is unsuitable for writing;
or the file was opened with the O_DIRECT flag, and either the address
specified in buf, the value specified
in count, or
the current file offset is not suitably aligned.
- EIO
-
A low-level I/O error occurred while modifying the
inode.
- ENOSPC
-
The device containing the file referred to by
fd has no room
for the data.
- EPIPE
-
fd is
connected to a pipe or socket whose reading end is
closed. When this happens the writing process will also
receive a SIGPIPE signal.
(Thus, the write return value is seen only if the
program catches, blocks or ignores this signal.)
Other errors may occur, depending on the object connected
to fd.
CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001.
Under SVr4 a write may be interrupted and return EINTR at
any point, not just before any data is written.
NOTES
A successful return from write() does not make any guarantee that
data has been committed to disk. In fact, on some buggy
implementations, it does not even guarantee that space has
successfully been reserved for the data. The only way to be
sure is to call fsync(2) after you are done
writing all your data.
SEE ALSO
close(2), fcntl(2), fsync(2), ioctl(2), lseek(2), open(2), pwrite(2), read(2), select(2), writev(2), fwrite(3)
This manpage is Copyright (C) 1992 Drew Eckhardt;
1993 Michael Haardt, Ian Jackson.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date. The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein. The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.
Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
Modified Sat Jul 24 13:35:59 1993 by Rik Faith <faith@cs.unc.edu>
Modified Sun Nov 28 17:19:01 1993 by Rik Faith <faith@cs.unc.edu>
Modified Sat Jan 13 12:58:08 1996 by Michael Haardt
<michael@cantor.informatik.rwth-aachen.de>
Modified Sun Jul 21 18:59:33 1996 by Andries Brouwer <aeb@cwi.nl>
2001-12-13 added remark by Zack Weinberg
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