ZMQ\_CONNECT(3) 0MQ Manual ZMQ\_CONNECT(3)

# [NAME](#NAME)

zmq\_connect - create outgoing connection from socket

# [SYNOPSIS](#SYNOPSIS)

**int zmq\_connect (void \*socket, const char \*endpoint);**

# [DESCRIPTION](#DESCRIPTION)

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)](/man/os/zeromq/zmq_tcp.7)

*ipc*

local inter-process communication transport, see [**zmq\_ipc**(7)](/man/os/zeromq/zmq_ipc.7)

*inproc*

local in-process (inter-thread) communication transport, see [**zmq\_inproc**(7)](/man/os/zeromq/zmq_inproc.7)

*pgm*, *epgm*

reliable multicast transport using PGM, see [**zmq\_pgm**(7)](/man/os/zeromq/zmq_pgm.7)

*vmci*

virtual machine communications interface (VMCI), see [**zmq\_vmci**(7)](/man/os/zeromq/zmq_vmci.7)

*udp*

unreliable unicast and multicast using UDP, see [**zmq\_udp**(7)](/man/os/zeromq/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)](/man/os/zeromq/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)](/man/os/zeromq/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.

# [RETURN VALUE](#RETURN_VALUE)

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

# [ERRORS](#ERRORS)

**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.

# [EXAMPLE](#EXAMPLE)

**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](#SEE_ALSO)

[**zmq\_bind**(3)](/man/os/zeromq/zmq_bind.3) [**zmq\_socket**(3)](/man/os/zeromq/zmq_socket.3) [**zmq**(7)](/man/os/zeromq/zmq.7)

# [AUTHORS](#AUTHORS)

This page was written by the 0MQ community. To make a change please read the 0MQ Contribution Policy at **http://www.zeromq.org/docs:contributing**.

08/29/2026 0MQ 4.3.5

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Document: zmq_connect(3) from zeromq 4.3.5-r13 (Chainguard OS)
Source: https://github.com/zeromq/libzmq