Sends bytes through a socket to any other socket.
    The $QIO equivalent is the IO$_WRITEVBLK function.
    Format
      #include  <types.h>
      #include  <socket.h>
      int sendto  ( int s, char *msg, int len, int flags, struct
                  sockaddr *to, int tolen ); (_DECC_V4_SOURCE)
      ssize_t sendto  ( int s, const void *msg, size_t len, int
                      flags, const struct sockaddr *to, size_t tolen
                      ); (not_DECC_V4_SOURCE)

1  –  Arguments

 s
    A socket descriptor created with the socket() function.
 msg
    A pointer to a buffer containing the data to be sent.
 len
    The length of the data pointed to by the msg argument.
 flags
    Can be either 0 or MSG_OOB. If it is MSG_OOB, the data is sent
    out of band. Data can be received before other pending data on
    the receiving socket if the receiver specifies MSG_OOB in the
    flag argument of its recv(), recvfrom()  or recvmsg() call.
 to
    Points to the address structure of the socket to which the data
    is to be sent.
 tolen
    The length of the address pointed to by the to argument.

2  –  Description

    This function can be used on sockets to send data to named
    sockets. The data in the msg buffer is sent to the socket whose
    address is specified in the to argument, and the address of
    socket s is provided to the receiving socket. The receiving
    socket gets the data using the read(), recv(),  recvfrom(), or
    recvmsg() function.
    Normally the sendto() function blocks if there is no space for
    the incoming data in the buffer. It waits until the buffer space
    becomes available. If the socket is set to nonblocking and there
    is no space for the data, the sendto() function fails with the
    EWOULDBLOCK error.
    If the message is too large to be sent in one piece, and the
    socket type is SOCK_DGRAM, which requires that messages be sent
    in one piece, sendto() fails with the EMSGSIZE error.
    If the address specified is a INADDR_BROADCAST address, then the
    SO_BROADCAST socket option must have been set and the process
    must have SYSPRV or BYPASS privilege for the I/O operation to
    succeed.
    A success return from the sendto() does not guarantee that
    the data has been received by the peer. All errors (except
    EWOULDBLOCK) are detected locally. To determine when it is
    possible to send more data, use the select() function.
    Related Functions
    See also read(), recv(),  recvfrom(), recvmsg(), socket(),  and
    getsockopt().

3  –  Return Values

    n                  The number of bytes sent. This value normally
                       equals len.
    -1                 Error; errno is set to indicate the error.

4  –  Errors

    EAFNOSUPPORT       Addresses in the specified address family
                       cannot be used with this socket.
    EBADF              The socket descriptor is invalid.
    ECONNRESET         A connection was forcibly closed by a peer.
    EDESTADDRREQ       You did not specify a destination address for
                       the connectionless socket and no peer address
                       is set.
    EFAULT             An invalid user space address is specified for
                       an argument.
    EHOSTUNREACH       The destination host is unreachable.
    EINTR              A signal interrupted sendto() before any data
                       was transmitted.
    EINVAL             The tolen argument is not a valid size for the
                       specified address family.
    EISCONN            The connection-oriented socket for which a
                       destination address was specified is already
                       connected.
    EMSGSIZE           The message is too large to be sent all at
                       once, as the socket requires.
    ENETDOWN           The local network connection is not
                       operational.
    ENETUNREACH        The destination network is unreachable.
    ENOBUFS            The system has insufficient resources to
                       complete the call.
    ENOMEM             The system did not have sufficient memory to
                       fulfill the request.
    ENOTCONN           The socket is connection-oriented but is not
                       connected.
    ENOTSOCK           The socket descriptor is invalid.
    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 is
                       connection oriented, and the peer is closed or
                       shut down for reading. In the latter case, if
                       the socket is of type SOCK_STREAM, the SIGPIPE
                       signal is generated to the calling process.
    EWOULDBLOCK        The socket is marked nonblocking, and no space
                       is available for the sendto() function.