modbus_new_tcp
Name
modbus_new_tcp - create a libmodbus context for TCP/IPv4
Synopsis
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
modbus_t *ctx;
ctx = modbus_new_tcp("127.0.0.1", 502);
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;
}