4.3BSD-UWisc/man/cat2/write.2
WRITE(2) UNIX Programmer's Manual WRITE(2)
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
_W_r_i_t_e attempts to write _n_b_y_t_e_s of data to the object refer-
enced by the descriptor _d from the buffer pointed to by _b_u_f.
_W_r_i_t_e_v performs the same action, but gathers the output data
from the _i_o_v_c_n_t buffers specified by the members of the _i_o_v
array: iov[0], iov[1], ..., iov[iovcnt-1].
For _w_r_i_t_e_v, the _i_o_v_e_c structure is defined as
struct iovec {
caddr_t iov_base;
int iov_len;
};
Each _i_o_v_e_c entry specifies the base address and length of an
area in memory from which data should be written. _W_r_i_t_e_v
will always write a complete area before proceeding to the
next.
On objects capable of seeking, the _w_r_i_t_e starts at a posi-
tion given by the pointer associated with _d, see _l_s_e_e_k(2).
Upon return from _w_r_i_t_e, 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 _w_r_i_t_e 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, _w_r_i_t_e and _w_r_i_t_e_v may write
Printed 12/27/86 May 14, 1986 1
WRITE(2) UNIX Programmer's Manual WRITE(2)
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 _e_r_r_n_o is set to indicate the error.
ERRORS
_W_r_i_t_e and _w_r_i_t_e_v 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 _i_o_v 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, _w_r_i_t_e_v may return one of the following errors:
[EINVAL] _I_o_v_c_n_t was less than or equal to 0, or
greater than 16.
[EINVAL] One of the _i_o_v__l_e_n values in the _i_o_v array
was negative.
Printed 12/27/86 May 14, 1986 2
WRITE(2) UNIX Programmer's Manual WRITE(2)
[EINVAL] The sum of the _i_o_v__l_e_n values in the _i_o_v
array overflowed a 32-bit integer.
SEE ALSO
fcntl(2), lseek(2), open(2), pipe(2), select(2)
Printed 12/27/86 May 14, 1986 3