write(2) -- Linux man page
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() 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 the file descriptor refers to
a regular file, 0 will be returned without causing any other effect.
For a special file, the results are not portable.
ERRORS
- EBADF
-
fd
is not a valid file descriptor or is not open for writing.
- EINVAL
-
fd
is attached to an object which is unsuitable 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 than the maximum allowed offset.
- 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.)
- EAGAIN
-
Non-blocking I/O has been selected using
O_NONBLOCK
and the write would block.
- EINTR
-
The call was interrupted by a signal before any data was written.
- ENOSPC
-
The device containing the file referred to by
fd
has no room for the data.
- EIO
-
A low-level I/O error occurred while modifying the inode.
Other errors may occur, depending on the object connected to
fd.
CONFORMING TO
SVr4, SVID, POSIX, X/OPEN, 4.3BSD. SVr4 documents additional error
conditions EDEADLK, ENOLCK, ENOLNK, ENOSR, ENXIO, or ERANGE.
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),
read(2),
select(2),
fwrite(3),
writev(3)
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