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 (con-
       sult 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 con-
       nectionless-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 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.


       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, 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
              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  speci-
              fied.

       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.  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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    SENDTO(3P)