---
name: "nng_listener_id"
section: "3"
platform: "linux"
package: "libnng-dev"
version: "1.10.1-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nng_listener_id"
---

# nng\_listener\_id(3)

return numeric listener identifier

## NAME

nng\_listener\_id - return numeric listener identifier

## SYNOPSIS

```
#include <nng/nng.h>
int nng_listener_id(nng_listener l);
```

## DESCRIPTION

The `nng_listener_id()` function returns a positive identifier for the listener *l*, if it is valid. Otherwise it returns `-1`.

**Note**\

A listener is considered valid if it was ever created with the `nng_listener_create()` or `nng_listen()` functions. listeners that are allocated on the stack or statically should be initialized with the macro `NNG_LISTENER_INITIALIZER` to ensure that they cannot be confused with a valid listener before they are created properly.

## RETURN VALUES

This function returns the positive value for the listener identifier, or `-1` if the listener is invalid.

## ERRORS

None.

## SEE ALSO

[nng\_listener(5)](/nng_listener/5.md), [nng(7)](/nng/7.md)