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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.
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 connectionless-mode, the
       message shall be sent to the address specified  by  dest_addr.  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 argu-
              ment are formed by logically OR'ing zero or more of the  follow-
              ing 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.

       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, the SIGPIPE signal is gener-
              ated 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
              A  component of a pathname exceeded {NAME_MAX} characters, or an
              entire pathname exceeded {PATH_MAX} characters.
       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 is not 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.  This error may or may not be returned for connection
              mode sockets.
       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
              Pathname  resolution of a symbolic link produced an intermediate
              result whose length 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(), recv(), recvfrom(), recvmsg(), select(), send(),
       sendmsg(), setsockopt(), shutdown(),  socket(),  the  Base  Definitions
       volume of IEEE Std 1003.1-2001, <sys/socket.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  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 .

IEEE/The Open Group                  2003                           SENDTO(3P)