SENDTO(3P) POSIX Programmer's Manual SENDTO(3P)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.
NAMEsendto — 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 (over‐
riding 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 pro‐
tocol).
MSG_OOB Sends out-of-band data on sockets that sup‐
port 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 privi‐
leges 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 connec‐
tion-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 path‐
name component names an existing file that is neither a direc‐
tory 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 fam‐
ily.
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 resolu‐
tion 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 ALSOgetsockopt(), 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 Electri‐
cal 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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SENDTO(3P)
