'\" t
.\"     Title: modbus_tcp_listen
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 02/28/2020
.\"    Manual: libmodbus Manual
.\"    Source: libmodbus v3.1.6
.\"  Language: English
.\"
.TH "MODBUS_TCP_LISTEN" "3" "02/28/2020" "libmodbus v3\&.1\&.6" "libmodbus Manual"
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.SH "NAME"
modbus_tcp_listen \- create and listen a TCP Modbus socket (IPv4)
.SH "SYNOPSIS"
.sp
\fBint modbus_tcp_listen(modbus_t *\fR\fB\fIctx\fR\fR\fB, int \fR\fB\fInb_connection\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fBmodbus_tcp_listen()\fR function shall create a socket and listen to maximum \fInb_connection\fR incoming connections on the specified IP address\&. The context _ctx _must be allocated and initialized with \fBmodbus_new_tcp\fR(3) before to set the IP address to listen, if IP address is set to NULL or \fI0\&.0\&.0\&.0\fR, any addresses will be listen\&.
.SH "RETURN VALUE"
.sp
The function shall return a new socket if successful\&. Otherwise it shall return \-1 and set errno\&.
.SH "EXAMPLE"
.sp
For detailed examples, see source files in tests directory:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
unit\-test\-server\&.c, simple but handle only one connection
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
bandwidth\-server\-many\-up\&.c, handles several connections at once
.RE
.sp
.if n \{\
.RS 4
.\}
.nf
\&.\&.\&.

/* To listen any addresses on port 502 */
ctx = modbus_new_tcp(NULL, 502);

/* Handle until 10 established connections */
server_socket = modbus_tcp_listen(ctx, 10);

/* Clear the reference set of socket */
FD_ZERO(&refset);

/* Add the server socket */
FD_SET(server_socket, &refset);

if (select(server_socket + 1, &refset, NULL, NULL, NULL) == \-1) {
}

\&.\&.\&.

close(server_socket);
modbus_free(ctx);
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBmodbus_new_tcp\fR(3) \fBmodbus_tcp_accept\fR(3) \fBmodbus_tcp_pi_listen\fR(3)
.SH "AUTHORS"
.sp
The libmodbus documentation was written by Stéphane Raimbault <stephane\&.raimbault@gmail\&.com>