libzmq/doc/zmq_send.txt

zmq_send(3)
===========


NAME
----
zmq_send - send a message on a socket


SYNOPSIS
--------
*int zmq_send (void '*socket', zmq_msg_t '*msg', int 'flags');*


DESCRIPTION
-----------
The _zmq_send()_ function shall queue the message referenced by the 'msg'
argument to be sent to the socket referenced by the 'socket' argument.  The
'flags' argument is a combination of the flags defined below:

*ZMQ_NOBLOCK*::
Specifies that the operation should be performed in non-blocking mode. If the
message cannot be queued on the underlying _message queue_ associated with
'socket', the _zmq_send()_ function shall fail with 'errno' set to EAGAIN.

*ZMQ_SNDMORE*::
Specifies that the message being sent is a multi-part message, and that further
message parts are to follow. Refer to the section regarding multi-part messages
below for a detailed description.

NOTE: A successful invocation of _zmq_send()_ does not indicate that the
message has been transmitted to the network, only that it has been queued on
the _message queue_ associated with the socket and 0MQ has assumed
responsibility for the message.


Multi-part messages
~~~~~~~~~~~~~~~~~~~
A 0MQ message is composed of 1 to N message parts; each message part is an
independent 'zmq_msg_t' in its own right. The total number of message parts is
unlimited. Consequently, wherever this documentation uses the term _message_ it
may be substituted for _message part_.

An application wishing to send a multi-part message does so by specifying the
'ZMQ_SNDMORE' flag to _zmq_send()_. The presence of this flag indicates to 0MQ
that the message being sent is a multi-part message and that more message parts
are to follow. When the application wishes to send the final message part it
does so by calling _zmq_send()_ without the 'ZMQ_SNDMORE' flag; this indicates
that no more message parts are to follow.

0MQ shall ensure the atomicity of a multi-part message; peers shall receive
either all _message parts_ of a multi-part message or none at all.


RETURN VALUE
------------
The _zmq_send()_ function shall return zero if successful. Otherwise it shall
return `-1` and set 'errno' to one of the values defined below.


ERRORS
------
*EAGAIN*::
Non-blocking mode was requested and the message cannot be queued at the moment.
*ENOTSUP*::
The _zmq_send()_ operation is not supported by this socket type.
*EFSM*::
The _zmq_send()_ operation cannot be performed on this socket at the moment due
to the socket not being in the appropriate state.  This error may occur with
socket types that switch between several states, such as ZMQ_REP.  See the
_messaging patterns_ section of linkzmq:zmq_socket[3] for more information.
*ETERM*::
The 0MQ 'context' associated with the specified 'socket' was terminated.


EXAMPLE
-------
.Filling in a message and sending it to a socket
----
/* Create a new message, allocating 6 bytes for message content */
zmq_msg_t msg;
int rc = zmq_msg_init_size (&msg, 6);
assert (rc == 0);
/* Fill in message content with 'AAAAAA' */
memset (zmq_msg_data (&msg), 'A', 6);
/* Send the message to the socket */
rc = zmq_send (socket, &msg, 0);
assert (rc == 0);
----

.Sending a multi-part message
----
/* Send a multi-part message consisting of three parts to socket */
rc = zmq_send (socket, &part1, ZMQ_SNDMORE);
rc = zmq_send (socket, &part2, ZMQ_SNDMORE);
/* Final part; no more parts to follow */
rc = zmq_send (socket, &part3, 0);
----


SEE ALSO
--------
linkzmq:zmq_recv[3]
linkzmq:zmq_socket[7]
linkzmq:zmq[7]


AUTHORS
-------
The 0MQ documentation was written by Martin Sustrik <sustrik@250bpm.com> and
Martin Lucina <mato@kotelna.sk>.