ØMQ Manual - ØMQ/4.2.2


zmq_connect - create outgoing connection from socket


int zmq_connect (void *socket, const char *endpoint);


The zmq_connect() function connects the socket to an endpoint and then accepts incoming connections on that endpoint.

The endpoint is a string consisting of a transport :// followed by an address. The transport specifies the underlying protocol to use. The address specifies the transport-specific address to connect to.

ØMQ provides the the following transports:

unicast transport using TCP, see zmq_tcp(7)
local inter-process communication transport, see zmq_ipc(7)
local in-process (inter-thread) communication transport, see zmq_inproc(7)
pgm, epgm
reliable multicast transport using PGM, see zmq_pgm(7)
virtual machine communications interface (VMCI), see zmq_vmci(7)

Every ØMQ socket type except ZMQ_PAIR supports one-to-many and many-to-one semantics. The precise semantics depend on the socket type and are defined in zmq_socket(3).

for most transports and socket types the connection is not performed immediately but as needed by ØMQ. Thus a successful call to zmq_connect() does not mean that the connection was or could actually be established. Because of this, for most transports and socket types the order in which a server socket is bound and a client socket is connected to it does not matter. The first exception is when using the inproc:// transport: you must call zmq_bind() before calling zmq_connect(). The second exception are ZMQ_PAIR sockets, which do not automatically reconnect to endpoints.

following a zmq_connect(), for socket types except for ZMQ_ROUTER, the socket enters its normal ready state. By contrast, following a zmq_bind() alone, the socket enters a mute state in which the socket blocks or drops messages according to the socket type, as defined in zmq_socket(3). A ZMQ_ROUTER socket enters its normal ready state for a specific peer only when handshaking is complete for that peer, which may take an arbitrary time.

Return value

The zmq_connect() function returns zero if successful. Otherwise it returns -1 and sets errno to one of the values defined below.


The endpoint supplied is invalid.
The requested transport protocol is not supported.
The requested transport protocol is not compatible with the socket type.
The ØMQ context associated with the specified socket was terminated.
The provided socket was invalid.
No I/O thread is available to accomplish the task.


Connecting a subscriber socket to an in-process and a tcp transport

/* Create a ZMQ_SUB socket */
void *socket = zmq_socket (context, ZMQ_SUB);
assert (socket);
/* Connect it to an in-process transport with the address 'my_publisher' */
int rc = zmq_connect (socket, "inproc://my_publisher");
assert (rc == 0);
/* Connect it to the host server001, port 5555 using a TCP transport */
rc = zmq_connect (socket, "tcp://server001:5555"); assert (rc == 0);

See also

zmq_bind(3) zmq_socket(3) zmq(7)


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