It's non-standard (although we have tried to get it added to the next Cxx standard) but you can use __attribute__((cleanup)) here. In systemd code it is common to write this as:
_cleanup_free_ float *x = malloc (...);
Since cleanups are supported by both GCC and Clang it's not a real problem to use them on Linux, BSD and MacOS. We recently added them to libvirt, have used them in libguestfs for a long time, and as I mention above they are used in systemd for years. They are also applicable to many other cases such as automatically closing files at the end of the current scope.
