SD_BUS_NEW(3)

  .SH "NAME" sd_bus_new, sd_bus_ref, sd_bus_unref, sd_bus_unrefp - Create a new bus object and create or destroy references to it
  .SH "SYNOPSIS"

#include <systemd/sd-bus.h>

      .HP u int sd_bus_new(sd_bus **bus);
      .HP u sd_bus *sd_bus_ref(sd_bus *bus);
      .HP u sd_bus *sd_bus_unref(sd_bus *bus);
      .HP u void sd_bus_unrefp(sd_bus **bus);

  .SH "DESCRIPTION"

    .PP 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).
    .PP In most cases, it is a better idea to invoke 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 calls not only allocate a bus object but also start the connection to a well-known bus in a single function invocation.
    .PP sd_bus_ref() increases the reference counter of bus by one.
    .PP 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.
    .PP 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 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)
                    fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
            ...
    }

    .PP sd_bus_ref(), sd_bus_unref() and sd_bus_unrefp() execute no operation if the passed in bus object is NULL.

  .SH "RETURN VALUE"

    .PP On success, sd_bus_new() returns 0 or a positive integer. On failure, it returns a negative errno-style error code.
    .PP sd_bus_ref() always returns the argument.
    .PP sd_bus_unref() always returns NULL.

  .SH "ERRORS"

    .PP Returned errors may indicate the following problems:

      .PP -ENOMEM

            Memory allocation failed.
          .RE

      .SH "NOTES"

        .PP sd_bus_new() and other functions described here are available as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

      .SH "SEE ALSO"

        .PP systemd(1), sd-bus(3), sd_bus_default_user(3), sd_bus_default_system(3), sd_bus_open_user(3), sd_bus_open_system(3)

NOTES

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