Manpages - zmq_connect.3

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.

0MQ provides the the following transports:

tcp

unicast transport using TCP, see *zmq_tcp*(7)

ipc

local inter-process communication transport, see *zmq_ipc*(7)

inproc

local in-process (inter-thread) communication transport, see *zmq_inproc*(7)

pgm, epgm

reliable multicast transport using PGM, see *zmq_pgm*(7)

vmci

virtual machine communications interface (VMCI), see *zmq_vmci*(7)

udp

unreliable unicast and multicast using UDP, see *zmq_udp*(7)

Every 0MQ socket type except ZMQ_PAIR and ZMQ_CHANNEL supports one-to-many and many-to-one semantics. The precise semantics depend on the socket type and are defined in *zmq_socket*(3).

Note

for most transports and socket types the connection is not performed immediately but as needed by 0MQ. 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 ZMQ_PAIR and ZMQ_CHANNEL sockets are an exception, as they do not automatically reconnect to endpoints.

Note

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.

Note

for some socket types, multiple connections to the same endpoint don’t really make sense (see https://github.com/zeromq/libzmq/issues/788). For those socket types, any attempt to connect to an already connected endpoint is silently ignored (i.e., returns zero). This behavior applies to ZMQ_DEALER, ZMQ_SUB, ZMQ_PUB, and ZMQ_REQ socket types.

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

EINVAL

The endpoint supplied is invalid.

EPROTONOSUPPORT

The requested transport protocol is not supported.

ENOCOMPATPROTO

The requested transport protocol is not compatible with the socket type.

ETERM

The 0MQ context associated with the specified socket was terminated.

ENOTSOCK

The provided socket was invalid.

EMTHREAD

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);

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

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