'\" t
.\"     Title: zmq_recvmsg
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 10/23/2023
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 4.3.5
.\"  Language: English
.\"
.TH "ZMQ_RECVMSG" "3" "10/23/2023" "0MQ 4\&.3\&.5" "0MQ Manual"
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.SH "NAME"
zmq_recvmsg \- receive a message part from a socket
.SH "SYNOPSIS"
.sp
\fBint zmq_recvmsg (void \fR\fB\fI*socket\fR\fR\fB, zmq_msg_t \fR\fB\fI*msg\fR\fR\fB, int \fR\fB\fIflags\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fIzmq_recvmsg()\fR function shall receive a message part from the socket referenced by the \fIsocket\fR argument and store it in the message referenced by the \fImsg\fR argument\&. Any content previously stored in \fImsg\fR shall be properly deallocated\&. If there are no message parts available on the specified \fIsocket\fR the \fIzmq_recvmsg()\fR function shall block until the request can be satisfied\&. The \fIflags\fR argument is a combination of the flags defined below:
.PP
\fBZMQ_DONTWAIT\fR
.RS 4
Specifies that the operation should be performed in non\-blocking mode\&. If there are no messages available on the specified
\fIsocket\fR, the
\fIzmq_recvmsg()\fR
function shall fail with
\fIerrno\fR
set to EAGAIN\&.
.RE
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.sp
this API method is deprecated in favor of zmq_msg_recv(3)\&.
.sp .5v
.RE
.SS "Multi\-part messages"
.sp
A 0MQ message is composed of 1 or more message parts\&. Each message part is an independent \fIzmq_msg_t\fR in its own right\&. 0MQ ensures atomic delivery of messages: peers shall receive either all \fImessage parts\fR of a message or none at all\&. The total number of message parts is unlimited except by available memory\&.
.sp
An application that processes multi\-part messages must use the \fIZMQ_RCVMORE\fR \fBzmq_getsockopt\fR(3) option after calling \fIzmq_recvmsg()\fR to determine if there are further parts to receive\&.
.SH "RETURN VALUE"
.sp
The \fIzmq_recvmsg()\fR function shall return number of bytes in the message if successful\&. Otherwise it shall return \-1 and set \fIerrno\fR to one of the values defined below\&.
.SH "ERRORS"
.PP
\fBEAGAIN\fR
.RS 4
Either the timeout set via the socket\-option ZMQ_RCVTIMEO (see
\fBzmq_setsockopt\fR(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\&.
.RE
.PP
\fBENOTSUP\fR
.RS 4
The
\fIzmq_recvmsg()\fR
operation is not supported by this socket type\&.
.RE
.PP
\fBEFSM\fR
.RS 4
The
\fIzmq_recvmsg()\fR
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
\fImessaging patterns\fR
section of
\fBzmq_socket\fR(3)
for more information\&.
.RE
.PP
\fBETERM\fR
.RS 4
The 0MQ
\fIcontext\fR
associated with the specified
\fIsocket\fR
was terminated\&.
.RE
.PP
\fBENOTSOCK\fR
.RS 4
The provided
\fIsocket\fR
was invalid\&.
.RE
.PP
\fBEINTR\fR
.RS 4
The operation was interrupted by delivery of a signal before a message was available\&.
.RE
.PP
\fBEFAULT\fR
.RS 4
The message passed to the function was invalid\&.
.RE
.SH "EXAMPLE"
.PP
\fBReceiving a message from a socket\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
/* Create an empty 0MQ message */
zmq_msg_t msg;
int rc = zmq_msg_init (&msg);
assert (rc == 0);
/* Block until a message is available to be received from socket */
rc = zmq_recvmsg (socket, &msg, 0);
assert (rc != \-1);
/* Release message */
zmq_msg_close (&msg);
.fi
.if n \{\
.RE
.\}
.PP
\fBReceiving a multi-part message\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
int more;
size_t more_size = sizeof (more);
do {
    /* Create an empty 0MQ message to hold the message part */
    zmq_msg_t part;
    int rc = zmq_msg_init (&part);
    assert (rc == 0);
    /* Block until a message is available to be received from socket */
    rc = zmq_recvmsg (socket, &part, 0);
    assert (rc != \-1);
    /* Determine if more message parts are to follow */
    rc = zmq_getsockopt (socket, ZMQ_RCVMORE, &more, &more_size);
    assert (rc == 0);
    zmq_msg_close (&part);
} while (more);
.fi
.if n \{\
.RE
.\}
.sp
.SH "SEE ALSO"
.sp
\fBzmq_recv\fR(3) \fBzmq_send\fR(3) \fBzmq_getsockopt\fR(3) \fBzmq_setsockopt\fR(3) \fBzmq_socket\fR(7) \fBzmq\fR(7)
.SH "AUTHORS"
.sp
This page was written by the 0MQ community\&. To make a change please read the 0MQ Contribution Policy at \m[blue]\fBhttp://www\&.zeromq\&.org/docs:contributing\fR\m[]\&.