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 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 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.   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 .