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modbus_tcp_listen

Name

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

Synopsis

int modbus_tcp_listen(modbus_t *ctx, int nb_connection);

Description

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 before to set the IP address to listen, if IP address is set to NULL or '0.0.0.0', any addresses will be listen.

Return value

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

Example

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);

See also