SENDTO
Section: POSIX Programmer's Manual (3P)
Updated: 2013
Index
Return to Main Contents
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
sendto
--- send a message on a socket
SYNOPSIS
#include <sys/socket.h>
ssize_t sendto(int socket, const void *message, size_t length,
int flags, const struct sockaddr *dest_addr,
socklen_t dest_len);
DESCRIPTION
The
sendto()
function shall send a message through a connection-mode or
connectionless-mode socket.
If the socket is a connectionless-mode socket, the message shall be sent
to the address specified by
dest_addr
if no pre-specified peer address has been set. If a peer address has
been pre-specified, either the message shall be sent to the address
specified by
dest_addr
(overriding the pre-specified peer address), or the function shall
return -1 and set
errno
to
[EISCONN].
If the socket is connection-mode,
dest_addr
shall be ignored.
The
sendto()
function takes the following arguments:
- socket
-
Specifies the socket file descriptor.
- message
-
Points to a buffer containing the message to be sent.
- length
-
Specifies the size of the message in bytes.
- flags
-
Specifies the type of message transmission. Values of this argument
are formed by logically OR'ing zero or more of the following flags:
-
- MSG_EOR
-
Terminates a record (if supported by the protocol).
- MSG_OOB
-
Sends out-of-band data on sockets that support out-of-band data. The
significance and semantics of out-of-band data are protocol-specific.
- MSG_NOSIGNAL
-
Requests not to send the SIGPIPE signal if an attempt to send is made
on a stream-oriented socket that is no longer connected. The
[EPIPE]
error shall still be returned.
- dest_addr
-
Points to a
sockaddr
structure containing the destination address. The length and format of
the address depend on the address family of the socket.
- dest_len
-
Specifies the length of the
sockaddr
structure pointed to by the
dest_addr
argument.
If the socket protocol supports broadcast and the specified address is
a broadcast address for the socket protocol,
sendto()
shall fail if the SO_BROADCAST option is not set for the socket.
The
dest_addr
argument specifies the address of the target.
The
length
argument specifies the length of the message.
Successful completion of a call to
sendto()
does not guarantee delivery of the message. A return value of -1
indicates only locally-detected errors.
If space is not available at the sending socket to hold the message to
be transmitted and the socket file descriptor does not have O_NONBLOCK
set,
sendto()
shall block until space is available. If space is not available at the
sending socket to hold the message to be transmitted and the socket
file descriptor does have O_NONBLOCK set,
sendto()
shall fail.
The socket in use may require the process to have appropriate
privileges to use the
sendto()
function.
RETURN VALUE
Upon successful completion,
sendto()
shall return the number of bytes sent. Otherwise, -1 shall be
returned and
errno
set to indicate the error.
ERRORS
The
sendto()
function shall fail if:
- EAFNOSUPPORT
-
Addresses in the specified address family cannot be used with this
socket.
- EAGAIN or EWOULDBLOCK
-
The socket's file descriptor is marked O_NONBLOCK and the requested
operation would block.
- EBADF
-
The
socket
argument is not a valid file descriptor.
- ECONNRESET
-
A connection was forcibly closed by a peer.
- EINTR
-
A signal interrupted
sendto()
before any data was transmitted.
- EMSGSIZE
-
The message is too large to be sent all at once, as the socket
requires.
- ENOTCONN
-
The socket is connection-mode but is not connected.
- ENOTSOCK
-
The
socket
argument does not refer to a socket.
- EOPNOTSUPP
-
The
socket
argument is associated with a socket that does not support one or more
of the values set in
flags.
- EPIPE
-
The socket is shut down for writing, or the socket is connection-mode
and is no longer connected. In the latter case, and if the socket is of
type SOCK_STREAM or SOCK_SEQPACKET and the MSG_NOSIGNAL flag is not set,
the SIGPIPE signal is generated to the calling thread.
If the address family of the socket is AF_UNIX, then
sendto()
shall fail if:
- EIO
-
An I/O error occurred while reading from or writing to the file
system.
- ELOOP
-
A loop exists in symbolic links encountered during resolution of the
pathname in the socket address.
- ENAMETOOLONG
-
The length of a component of a pathname is longer than
{NAME_MAX}.
- ENOENT
-
A component of the pathname does not name an existing file or the
pathname is an empty string.
- ENOTDIR
-
A component of the path prefix of the pathname in the socket address
names an existing file that is neither a directory nor a symbolic link
to a directory, or the pathname in the socket address contains at
least one non-<slash>
character and ends with one or more trailing
<slash>
characters and the last pathname component names an existing file that
is neither a directory nor a symbolic link to a directory.
The
sendto()
function may fail if:
- EACCES
-
Search permission is denied for a component of the path prefix; or
write access to the named socket is denied.
- EDESTADDRREQ
-
The socket is not connection-mode and does not have its peer address
set, and no destination address was specified.
- EHOSTUNREACH
-
The destination host cannot be reached (probably because the host is
down or a remote router cannot reach it).
- EINVAL
-
The
dest_len
argument is not a valid length for the address family.
- EIO
-
An I/O error occurred while reading from or writing to the file
system.
- EISCONN
-
A destination address was specified and the socket is already
connected.
- ENETDOWN
-
The local network interface used to reach the destination is down.
- ENETUNREACH
-
No route to the network is present.
- ENOBUFS
-
Insufficient resources were available in the system to perform the
operation.
- ENOMEM
-
Insufficient memory was available to fulfill the request.
If the address family of the socket is AF_UNIX, then
sendto()
may fail if:
- ELOOP
-
More than
{SYMLOOP_MAX}
symbolic links were encountered during resolution of the pathname in
the socket address.
- ENAMETOOLONG
-
The length of a pathname exceeds
{PATH_MAX},
or pathname resolution of a symbolic link produced an intermediate
result with a length that exceeds
{PATH_MAX}.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The
select()
and
poll()
functions can be used to determine when it is possible to send more
data.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
getsockopt(),
poll(),
pselect(),
recv(),
recvfrom(),
recvmsg(),
send(),
sendmsg(),
setsockopt(),
shutdown(),
socket()
The Base Definitions volume of POSIX.1-2008,
<sys_socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
|
|
- Running on 
-
:
: 