WRITE(2-BSD) RISC/os Reference Manual WRITE(2-BSD)
NAME
write, writev - write output
SYNOPSIS
cc = write(d, buf, nbytes)
int cc, d;
char *buf;
int nbytes;
#include <sys/types.h>
#include <sys/uio.h>
cc = writev(d, iov, iovcnt)
int cc, d;
struct iovec *iov;
int iovcnt;
DESCRIPTION
write attempts to write nbytes of data to the object refer-
enced by the descriptor d from the buffer pointed to by buf.
writev performs the same action, but gathers the output data
from the iovcnt buffers specified by the members of the iov
array: iov[0], iov[1], ..., iov[iovcnt-1].
For writev, the iovec structure is defined as
struct iovec {
caddr_t iov_base;
int iov_len;
};
Each iovec entry specifies the base address and length of an
area in memory from which data should be written. writev
will always write a complete area before proceeding to the
next.
On objects capable of seeking, the write starts at a posi-
tion given by the pointer associated with d, see lseek(2).
Upon return from write, the pointer is incremented by the
number of bytes actually written.
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.
If the real user is not the super-user, then write clears
the set-user-id bit on a file. This prevents penetration of
system security by a user who "captures" a writable set-
user-id file owned by the super-user.
When using non-blocking I/O on objects such as sockets that
are subject to flow control, write and writev may write
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WRITE(2-BSD) RISC/os Reference Manual WRITE(2-BSD)
fewer bytes than requested; the return value must be noted,
and the remainder of the operation should be retried when
possible.
RETURN VALUE
Upon successful completion the number of bytes actually
written is returned. Otherwise a -1 is returned and the
global variable errno is set to indicate the error.
ERRORS
write and writev will fail and the file pointer will remain
unchanged if one or more of the following are true:
[EBADF] d is not a valid descriptor open for writing.
[EPIPE] An attempt is made to write to a pipe that is
not open for reading by any process.
[EPIPE] An attempt is made to write to a socket of
type SOCK_STREAM that is not connected to a
peer socket.
[EFBIG] An attempt was made to write a file that
exceeds the process's file size limit or the
maximum file size.
[EFAULT] Part of iov or data to be written to the file
points outside the process's allocated
address space.
[EINVAL] The pointer associated with d was negative.
[ENOSPC] There is no free space remaining on the file
system containing the file.
[EDQUOT] The user's quota of disk blocks on the file
system containing the file has been
exhausted.
[EIO] An I/O error occurred while reading from or
writing to the file system.
[EWOULDBLOCK] The file was marked for non-blocking I/O, and
no data could be written immediately.
In addition, writev may return one of the following errors:
[EINVAL] iovcnt was less than or equal to 0, or
greater than 16.
[EINVAL] One of the iov_len values in the iov array
was negative.
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WRITE(2-BSD) RISC/os Reference Manual WRITE(2-BSD)
[EINVAL] The sum of the iov_len values in the iov
array overflowed a 32-bit integer.
SEE ALSO
fcntl(2), lseek(2), open(2), pipe(2), select(2).
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