sd_bus_new

elogind
sd_bus_new 3
sd_bus_new sd_bus_ref sd_bus_unref sd_bus_unrefp sd_bus_close_unref sd_bus_close_unrefp sd_bus_flush_close_unref sd_bus_flush_close_unrefp Create a new bus object and create or destroy references to it

    #include <elogind/sd-bus.h>

int `sd_bus_new` sd_bus **bus sd_bus *`sd_bus_ref` sd_bus *bus sd_bus *`sd_bus_unref` sd_bus *bus sd_bus *`sd_bus_close_unref` sd_bus *bus sd_bus *`sd_bus_flush_close_unref` sd_bus *bus void `sd_bus_unrefp` sd_bus **busp void `sd_bus_close_unrefp` sd_bus **busp void `sd_bus_flush_close_unrefp` sd_bus **busp

## Description

`sd_bus_new()` creates a new bus object. This object is reference-counted, and will be destroyed when all references are gone. Initially, the caller of this function owns the sole reference and the bus object will not be connected to any bus. To connect it to a bus, make sure to set an address with sd_bus_set_address 3 or a related call, and then start the connection with sd_bus_start 3.

In most cases, it is better to use sd_bus_default_user 3, sd_bus_default_system 3 or related calls instead of the more low-level `sd_bus_new()` and `sd_bus_start()`. The higher-level functions not only allocate a bus object but also start the connection to a well-known bus in a single function call.

`sd_bus_ref()` increases the reference counter of bus by one.

`sd_bus_unref()` decreases the reference counter of bus by one. Once the reference count has dropped to zero, bus is destroyed and cannot be used anymore, so further calls to `sd_bus_ref()` or `sd_bus_unref()` are illegal.

`sd_bus_unrefp()` is similar to `sd_bus_unref()` but takes a pointer to a pointer to an sd_bus object. This call is useful in conjunction with GCC's and LLVM's Clean-up Variable Attribute. Note that this function is defined as an inline function. Use a declaration like the following, in order to allocate a bus object that is freed automatically as the code block is left:

    {
      __attribute__((cleanup(sd_bus_unrefp))) sd_bus *bus = NULL;
      int r;
      …
      r = sd_bus_default(&bus);
      if (r < 0) {
        errno = -r;
        fprintf(stderr, "Failed to allocate bus: %m\n");
      }
      …
    }

`sd_bus_ref()` and `sd_bus_unref()` execute no operation if the argument is `NULL`. `sd_bus_unrefp()` will first dereference its argument, which must not be `NULL`, and will execute no operation if that is `NULL`.

`sd_bus_close_unref()` is similar to `sd_bus_unref()`, but first executes sd_bus_close 3, ensuring that the connection is terminated before the reference to the connection is dropped and possibly the object freed.

`sd_bus_flush_close_unref()` is similar to `sd_bus_unref()`, but first executes sd_bus_flush 3 as well as sd_bus_close 3, ensuring that any pending messages are synchronously flushed out before the reference to the connection is dropped and possibly the object freed. This call is particularly useful immediately before exiting from a program as it ensures that any pending outgoing messages are written out, and unprocessed but queued incoming messages released before the connection is terminated and released.

`sd_bus_close_unrefp()` is similar to `sd_bus_close_unref()`, but may be used in GCC's and LLVM's Clean-up Variable Attribute, see above. Similarly, `sd_bus_flush_close_unrefp()` is similar to `sd_bus_flush_close_unref()`.

## Return Value

On success, `sd_bus_new()` returns 0 or a positive integer. On failure, it returns a negative errno-style error code.

`sd_bus_ref()` always returns the argument.

`sd_bus_unref()` and `sd_bus_flush_close_unref()` always return `NULL`.

### Errors

Returned errors may indicate the following problems:

`-ENOMEM`

  Memory allocation failed.

## History

`sd_bus_new()`, `sd_bus_ref()`, and `sd_bus_unref()` were added in version 209.

`sd_bus_unrefp()` was added in version 229.

`sd_bus_flush_close_unref()` and `sd_bus_flush_close_unrefp()` were added in version 240.

`sd_bus_close_unref()` and `sd_bus_close_unrefp()` were added in version 241.

## See Also

elogind 8, sd-bus 3, sd_bus_default_user 3, sd_bus_default_system 3, sd_bus_open_user 3, sd_bus_open_system 3, sd_bus_close 3