modbus_new_tcp(3)
=================


NAME
----
modbus_new_tcp - create a libmodbus context for TCP/IPv4


SYNOPSIS
--------
*modbus_t *modbus_new_tcp(const char *'ip', int 'port');*


DESCRIPTION
-----------
The *modbus_new_tcp()* function shall allocate and initialize a modbus_t
structure to communicate with a Modbus TCP IPv4 server.

The _ip_ argument specifies the IP address of the server to which the client
wants to establish a connection. A NULL value can be used to listen any addresses in
server mode.

The _port_ argument is the TCP port to use. Set the port to
`MODBUS_TCP_DEFAULT_PORT` to use the default one (502). It’s convenient to use a
port number greater than or equal to 1024 because it’s not necessary to have
administrator privileges.


RETURN VALUE
------------
The function shall return a pointer to a *modbus_t* structure if
successful. Otherwise it shall return NULL and set errno to one of the values
defined below.


ERRORS
------
*EINVAL*::
An invalid IP address was given.

*ENOMEM*::
Out of memory. Possibly, the application hits its memory limit and/or whole
system is running out of memory.


EXAMPLE
-------
[source,c]
-------------------
modbus_t *ctx;

ctx = modbus_new_tcp("127.0.0.1", 1502);
if (ctx == NULL) {
    fprintf(stderr, "Unable to allocate libmodbus context\n");
    return -1;
}

if (modbus_connect(ctx) == -1) {
    fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
    modbus_free(ctx);
    return -1;
}
-------------------

SEE ALSO
--------
linkmb:modbus_tcp_listen[3]
linkmb:modbus_free[3]


AUTHORS
-------
The libmodbus documentation was written by Stéphane Raimbault
<stephane.raimbault@gmail.com>
