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zmq_sendmsg - send a message part on a socket
*int zmq_sendmsg (void '*socket', zmq_msg_t '*msg', int 'flags');*
The _zmq_sendmsg()_ 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:
Specifies that the operation should be performed in non-blocking mode. If the
message cannot be queued on the 'socket', the _zmq_sendmsg()_ function shall
fail with 'errno' set to EAGAIN.
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.
The _zmq_msg_t_ structure passed to _zmq_sendmsg()_ is nullified during the
call. If you want to send the same message to multiple sockets you have to copy
it using (e.g. using _zmq_msg_copy()_).
NOTE: A successful invocation of _zmq_sendmsg()_ does not indicate that the
message has been transmitted to the network, only that it has been queued on
the 'socket' and 0MQ has assumed responsibility for the message.
Multi-part messages
A 0MQ message is composed of 1 or more message parts. Each message
part is an independent 'zmq_msg_t' in its own right. 0MQ ensures atomic
delivery of messages; peers shall receive either all _message parts_ of a
message or none at all. The total number of message parts is unlimited except
by available memory.
An application that sends multipart messages must use the _ZMQ_SNDMORE_ flag
when sending each data part except the final one.
The _zmq_sendmsg()_ function shall return number of bytes in the message
if successful. Otherwise it shall return `-1` and set 'errno' to one of the
values defined below.
Non-blocking mode was requested and the message cannot be sent at the moment.
The _zmq_sendmsg()_ operation is not supported by this socket type.
The _zmq_sendmsg()_ 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.
The 0MQ 'context' associated with the specified 'socket' was terminated.
The provided 'socket' was invalid.
The operation was interrupted by delivery of a signal before the message was
Invalid message.
Message cannot be routed to the destination specified as the peer is either
dead or disconnected. This error makes sense only with ZMQ_ROUTER socket.
.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_sendmsg (socket, &msg, 0);
assert (rc == 6);
.Sending a multi-part message
/* Send a multi-part message consisting of three parts to socket */
rc = zmq_sendmsg (socket, &part1, ZMQ_SNDMORE);
rc = zmq_sendmsg (socket, &part2, ZMQ_SNDMORE);
/* Final part; no more parts to follow */
rc = zmq_sendmsg (socket, &part3, 0);
+This man page was written by Martin Sustrik <>, Martin
+Lucina <> and Pieter Hintjens <>.
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