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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.1‐2017, <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 .