ZMQ_RECV - Online Linux Manual PageSection : 3
Updated : 01/21/2023
Source : 0MQ 4​.3​.4
Note : 0MQ Manual

NAMEzmq_recv − receive a message part from a socket

SYNOPSISint zmq_recv (void *socket, void *buf, size_t len, int flags);

DESCRIPTIONThe zmq_recv() function shall receive a message from the socket referenced by the socket argument and store it in the buffer referenced by the buf argument​. Any bytes exceeding the length specified by the len argument shall be truncated​. If there are no messages available on the specified socket the zmq_recv() function shall block until the request can be satisfied​. The flags argument is a combination of the flags defined below: The buf argument may be null if len is zero​. ZMQ_DONTWAIT Specifies that the operation should be performed in non−blocking mode​. If there are no messages available on the specified socket, the zmq_recv() function shall fail with errno set to EAGAIN​.

Multi−part messagesA 0MQ message is composed of 1 or more message parts​. 0MQ ensures atomic delivery of messages: peers shall receive either all message parts of a message or none at all​. The total number of message parts is unlimited except by available memory​. An application that processes multi−part messages must use the ZMQ_RCVMORE zmq_getsockopt(3) option after calling zmq_recv() to determine if there are further parts to receive​.

RETURN VALUEThe zmq_recv() function shall return number of bytes in the message if successful​. Note that the value can exceed the value of the len parameter in case the message was truncated​. If not successful the function shall return −1 and set errno to one of the values defined below​.

ERRORSEAGAIN Either the timeout set via the socket−option ZMQ_RCVTIMEO (see zmq_setsockopt(3)) has been reached (flag ZMQ_DONTWAIT not set) without being able to read a message from the socket or there are no messages available at the moment (flag ZMQ_DONTWAIT set) and the operation would block​. ENOTSUP The zmq_recv() operation is not supported by this socket type​. EFSM The zmq_recv() operation cannot be performed on this socket at the moment due to the socket not being in the appropriate state​. This error may occur with socket types that switch between several states, such as ZMQ_REP​. See the messaging patterns section of zmq_socket(3) for more information​. ETERM The 0MQ context associated with the specified socket was terminated​. ENOTSOCK The provided socket was invalid​. EINTR The operation was interrupted by delivery of a signal before a message was available​.

EXAMPLEReceiving a message from a socket. char buf [256]; nbytes = zmq_recv (socket, buf, 256, 0); assert (nbytes != −1);

SEE ALSOzmq_send(3) zmq_getsockopt(3) zmq_setsockopt(3) zmq_socket(7) zmq(7)

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