__uuidof in C Master Volume Windows

Question

I want to change master volume with C, but __uuidof is only for C++; what can I use instead of that?

const CLSID CLSID_MMDeviceEnumerator = __uuidof(MMDeviceEnumerator);
const IID IID_IMMDeviceEnumerator = __uuidof(IMMDeviceEnumerator);
hr = CoCreateInstance(
     CLSID_MMDeviceEnumerator, NULL,
     CLSCTX_ALL, IID_IMMDeviceEnumerator,
     (void**)&deviceEnumerator);

I only found that: Alternative to __uuidof in C

Answer 1

CLSID_MMDeviceEnumerator and IID_IMMDeviceEnumerator are defined in your API's header file, i.e. <mmdeviceapi.h>.

You have to use these definitions in your C code, instead of __uuidof, as this is only available for C++ code.

Note that you need to include <initguid.h> before <mmdeviceapi.h>:

#include <initguid.h>
#include <mmdeviceapi.h>

Then this code should work:

hr = CoCreateInstance(
    &CLSID_MMDeviceEnumerator, (*)
    NULL,
    CLSCTX_ALL, 
    &IID_IMMDeviceEnumerator,  (*)
    (void**)&deviceEnumerator
);

(*) Note that I've used the & (address-of), since in C++ you have references, but in C code you need to be explicit using pointers.