---
name: "sd_bus_message_is_empty"
section: "3"
platform: "linux"
package: "libsystemd-dev"
version: "257.13-1~deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_message_get_signature"
---

# sd\_bus\_message\_is\_empty(3)

Query bus message signature

Part of [sd\_bus\_message\_get\_signature(3)](/sd_bus_message_get_signature/3.md).

## NAME

sd\_bus\_message\_get\_signature, sd\_bus\_message\_is\_empty, sd\_bus\_message\_has\_signature - Query bus message signature

## SYNOPSIS

```
#include <systemd/sd-bus.h>
```

**const char\* sd\_bus\_message\_get\_signature(sd\_bus\_message \****message***, int** *complete***);**

**int sd\_bus\_message\_is\_empty(sd\_bus\_message \****message***);**

**int sd\_bus\_message\_has\_signature(sd\_bus\_message \****message***, const char \****signature***);**

## DESCRIPTION

**sd\_bus\_message\_get\_signature()** returns the signature of message *message*. If *complete* is true, the signature of the whole message is returned, and just the signature of the currently open container otherwise.

**sd\_bus\_message\_is\_empty()** returns true if the message is empty, i.e. when its signature is empty.

**sd\_bus\_message\_has\_signature()** returns true if the signature of the message *message* matches given *signature*. Parameter *signature* may be **NULL**, this is treated the same as an empty string, which is equivalent to calling **sd\_bus\_message\_is\_empty()**.

## RETURN VALUE

On success, **sd\_bus\_message\_get\_signature()** returns the signature, and **NULL** on error.

The other functions return 0 or a positive integer on success. On failure, they return a negative errno-style error code.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

The *message* parameter is **NULL**.

**NULL**

The *message* parameter is **NULL**.

## NOTES

Functions described here are available as a shared library, which can be compiled against and linked to with the **libsystemd** [**pkg-config**(1)](/pkg-config/1.md) file.

The code described here uses [**getenv**(3)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) from a parallel thread. It is recommended to only do calls to **setenv()** from an early phase of the program when no other threads have been started.

## HISTORY

**sd\_bus\_message\_get\_signature()**, **sd\_bus\_message\_is\_empty()**, and **sd\_bus\_message\_has\_signature()** were added in version 240.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_message\_new**(3)](/sd_bus_message_new/3.md)