---
name: "zmq_connect_peer"
section: "3"
platform: "linux"
package: "zeromq"
version: "4.3.5-3"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/zmq_connect_peer"
---

# zmq\_connect\_peer(3)

create outgoing connection from socket and return the connection routing id in thread-safe and atomic way.

## NAME

zmq\_connect\_peer - create outgoing connection from socket and return the connection routing id in thread-safe and atomic way.

## SYNOPSIS

**uint32\_t zmq\_connect\_peer (void** *\*socket***, const char** *\*endpoint***);**

## DESCRIPTION

The *zmq\_connect\_peer()* function connects a *ZMQ\_PEER* socket to an *endpoint* and then returns the endpoint *routing\_id*.

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.

The function is supported only on the *ZMQ\_PEER* socket type and would return 0 with *errno* set to *ENOTSUP* otherwise.

The *zmq\_connect\_peer()* support the following transports:

*tcp*

unicast transport using TCP, see [**zmq\_tcp**(7)](/zmq_tcp/7.md)

*ipc*

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

*inproc*

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

*ws*

unicast transport using WebSockets, see **zmq\_ws**(7)

*wss*

unicast transport using WebSockets over TLS, see **zmq\_wss**(7)

## RETURN VALUE

The *zmq\_connect\_peer()* function returns the peer *routing\_id* if successful. Otherwise it returns 0 and sets *errno* to one of the values defined below.

## ERRORS

**EINVAL**

The endpoint supplied is invalid.

**EPROTONOSUPPORT**

The requested *transport* protocol is not supported with *ZMQ\_PEER*.

**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.

**ENOTSUP**

The socket is not of type *ZMQ\_PEER*.

**EFAULT**

The *ZMQ\_IMMEDIATE* option is set on the socket.

## EXAMPLE

**Connecting a peer socket to a TCP transport and sending a message**.

```
/* Create a ZMQ_SUB socket */
void *socket = zmq_socket (context, ZMQ_PEER);
assert (socket);
/* Connect it to the host server001, port 5555 using a TCP transport */
uint32_t routing_id = zmq_connect (socket, "tcp://server001:5555");
assert (routing_id == 0);
/* Sending a message to the peer  */
zmq_msg_t msg;
int rc = zmq_msg_init_data (&msg, "HELLO", 5, NULL, NULL);
assert (rc == 0);
rc = zmq_msg_set_routing_id (&msg, routing_id);
assert (rc == 0);
rc = zmq_msg_send (&msg, socket, 0);
assert (rc == 5);
rc = zmq_msg_close (&msg);
assert (rc == 0);
```

## SEE ALSO

[**zmq\_connect**(3)](/zmq_connect/3.md) [**zmq\_bind**(3)](/zmq_bind/3.md) [**zmq\_socket**(3)](/zmq_socket/3.md) [**zmq**(7)](/zmq/7.md)

## 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**.