---
name: "sd_bus_message_get_signature"
section: "3"
platform: "linux"
package: "systemd-libs"
version: "262.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_message_get_signature"
---

# sd\_bus\_message\_get\_signature(3)

Query bus message signature

## 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.

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel.

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)