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Man Pages
MODBUS_TCP_LISTEN(3) libmodbus Manual MODBUS_TCP_LISTEN(3)

modbus_tcp_listen - create and listen a TCP Modbus socket (IPv4)

int modbus_tcp_listen(modbus_t *ctx, int nb_connection );

The modbus_tcp_listen() function shall create a socket and listen to maximum nb_connection incoming connections on the specified IP address. The context _ctx _must be allocated and initialized with modbus_new_tcp(3) before to set the IP address to listen, if IP address is set to NULL, any addresses will be listen.

The function shall return a new socket if successful. Otherwise it shall return -1 and set errno.

For detailed examples, see source files in tests directory:
•unit-test-server.c, simple but handle only one connection
•bandwidth-server-many-up.c, handles several connections at once
...
/* 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);

modbus_new_tcp(3) modbus_tcp_accept(3) modbus_tcp_pi_listen(3)

The libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com>
12/20/2018 libmodbus v3.1.4

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