SENDTO(3)                  POSIX Programmer's Manual                 SENDTO(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.1-2017, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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 .



IEEE/The Open Group                  2017                            SENDTO(3)
