= zmq_connect(3)


== NAME
zmq_connect - create outgoing connection from socket


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


== 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 xref:zmq_tcp.adoc[zmq_tcp]
'ipc':: local inter-process communication transport, see xref:zmq_ipc.adoc[zmq_ipc]
'inproc':: local in-process (inter-thread) communication transport, see xref:zmq_inproc.adoc[zmq_inproc]
'pgm', 'epgm':: reliable multicast transport using PGM, see xref:zmq_pgm.adoc[zmq_pgm]
'vmci':: virtual machine communications interface (VMCI), see xref:zmq_vmci.adoc[zmq_vmci]
'udp':: unreliable unicast and multicast using UDP, see xref:zmq_udp.adoc[zmq_udp]

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
xref:zmq_socket.adoc[zmq_socket]

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
xref:zmq_socket.adoc[zmq_socket] 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
The _zmq_connect()_ function returns zero if successful. Otherwise it returns
`-1` 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.
*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
.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
* xref:zmq_bind.adoc[zmq_bind]
* xref:zmq_socket.adoc[zmq_socket]
* xref:zmq.adoc[zmq]


== AUTHORS
This page was written by the 0MQ community. To make a change please
read the 0MQ Contribution Policy at <https://zeromq.org/how-to-contribute/>.
