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sendmsg(2)
NAME
  sendmsg - Sends a message from a socket using a message structure

SYNOPSIS
  #include <sys/socket.h>
  ssize_t sendmsg (
	  int socket,
	  const struct msghdr *message,
	  int flags );

  [Digital]  The following definition of the sendmsg) function does not
  conform to current standards and is supported only for backward
  compatibility (see standards(5)):

  int sendmsg (
	  int socket,
	  struct msghdr *message,
	  int flags );


STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  sendmsg():  XPG4-UNIX

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  socket    Specifies the socket descriptor.

  message   Points to a msghdr structure, containing pointers to both the
	    destination address for the outgoing message and to buffers
	    containing ancillary data. The format of the address is
	    determined by the behavior requested for the socket.

	    [Digital] If the compile-time option _SOCKADDR_LEN is defined
	    before the <sys/socket.h> header file is included, the msghdr
	    structure takes 4.4BSD behavior.  Otherwise, the default 4.3BSD
	    msghdr structure is used.

	    In 4.4BSD, the msghdr structure has a separate msg_flags field
	    for holding flags from the received message.  In addition, the
	    msg_accrights field is generalized into a msg_control field.  See
	    the recvmsg() function for more information.

	    If _SOCKADDR_LEN is defined, the 4.3BSD msghdr structure is
	    defined with the name omsghdr.

  flags	    Allows the sender to control the message transmission.  The
	    <sys/socket.h> file contains the flags values.  The flags value
	    to send a call is formed by a logical OR of one or both of the
	    following values:

	    MSG_OOB	   Processes out-of-band data on sockets that support
			   out-of-band data.

	    MSG_DONTROUTE  Sends without using routing tables.	(Not
			   recommended, for debugging purposes only.)

DESCRIPTION
  The sendmsg() function sends messages through connected or unconnected
  sockets using the msghdr message structure.  This minimizes the number of
  directly supplied parameters to the function call. The <sys/socket.h> file
  contains the msghdr structure and defines the structure members.

  To broadcast on a socket, the application program must first issue a
  setsockopt() function using the SO_BROADCAST option to gain broadcast
  permissions.

NOTES
  [Digital]  When compiled in the X/Open UNIX environment, calls to the
  sendmsg() function are internally renamed by prepending _E to the function
  name. When you are debugging a module that includes the sendmsg() function
  and for which _XOPEN_SOURCE_EXTENDED has been defined, use _Esendmsg to
  refer to the sendmsg() call.	See standards(5) for further information.

RETURN VALUES
  Upon successful completion, the sendmsg() function returns the number of
  characters sent.  Otherwise, a value of -1 is returned and errno is set to
  indicate the error.

ERRORS
  If the sendmsg() function fails, errno may be set to one of the following
  values:

  [EACCESS]	 Search permission is denied for a component of the path
		 prefix; or write access to the named socket is denied.

  [EAFNOSUPPORT] Addresses in the specified address family cannot be used
		 with this socket.

  [EBADF]	 The socket parameter is not valid.

  [ECONNRESET]	 A connection was forcibly closed by a peer.

  [EINTR]	 A signal interrupted sendmsg before any data was
		 transmitted.

  [EINVAL]	 The sum of the iov_len values overflows an ssize_t.

  [EIO]		 An I/O error occurred while reading from or writing to the
		 file system.

  [ELOOP]	 Too many symbolic links were encountered in translating the
		 pathname in the socket address.

  [EMSGSIZE]	 The message is too large to be sent all at once, as the
		 socket requires.

  [ENAMETOOLONG] A component of the 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.

  [ENOTCONN]	 A socket is connection-oriented but is not connected.

  [ENOTDIR]	 A component of the path prefix of the pathname in address
		 is not a directory.

  [ENOTSOCK]	 The socket parameter refers to a file, not 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-oriented and the peer is closed or shut down for
		 reading. In the latter case, and 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 sendmsg() function.

RELATED INFORMATION
  Functions: recv(2), recvfrom(2), recvmsg(2), send(2), sendto(2),
  shutdown(2), socket(2), select(2), getsockopt(2), setsockopt(2)

  Standards: standards(5)