# sd_bus_new

## NAME



           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
    


## SYNOPSIS



           **#include <systemd/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******[1].
           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.
    


## NOTES



           Functions described here are available as a shared library, which
           can be compiled against and linked to with the
           **libsystemd pkg-config**(1) file.
    
           The code described here uses getenv(3), which is declared to be
           not multi-thread-safe. This means that the code calling the
           functions described here must not call setenv(3) 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.
    


## NOTES



            1. Clean-up Variable Attribute
               https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
    


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