---
name: "modbus_new_tcp_pi"
section: "3"
platform: "linux"
package: "libmodbus-dev"
version: "3.1.6-2.1"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/modbus_new_tcp_pi"
---

# modbus\_new\_tcp\_pi(3)

create a libmodbus context for TCP Protocol Independent

## NAME

modbus\_new\_tcp\_pi - create a libmodbus context for TCP Protocol Independent

## SYNOPSIS

**modbus\_t \*modbus\_new\_tcp\_pi(const char \****node***, const char \****service***);**

## DESCRIPTION

The **modbus\_new\_tcp\_pi()** function shall allocate and initialize a modbus\_t structure to communicate with a Modbus TCP IPv4 or IPv6 server.

The *node* argument specifies the host name or IP address of the host to connect to, eg. "192.168.0.5" , "::1" or "server.com". A NULL value can be used to listen any addresses in server mode.

The *service* argument is the service name/port number to connect to. To use the default Modbus port use the string "502". On many Unix systems, 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**

The node string is empty or has been truncated. The service string is empty or has been truncated.

**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_pi("::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

[**modbus\_new\_tcp**(3)](/modbus_new_tcp/3.md) [**modbus\_tcp\_pi\_listen**(3)](/modbus_tcp_pi_listen/3.md) [**modbus\_free**(3)](/modbus_free/3.md)

## AUTHORS

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