IAudioEndpointVolume has no member named GetMasterVolumeLevelScalar - c++

Question

Consider this program:
#include <stdio.h>
#include <windows.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>
#include <math.h>
int main() {
IAudioEndpointVolume *wh;
IMMDevice *ya;
IMMDeviceEnumerator *xr;
CoInitialize(0);
CoCreateInstance(__uuidof(MMDeviceEnumerator), 0, CLSCTX_INPROC_SERVER,
__uuidof(IMMDeviceEnumerator), (void**)&xr);
xr->GetDefaultAudioEndpoint(eRender, eConsole, &ya);
ya->Activate(__uuidof(IAudioEndpointVolume), CLSCTX_ALL, 0, (void**)&wh);
float zu;
wh->GetMasterVolumeLevelScalar(&zu);
printf("%d\n", (int) round(100 * zu));
}
I can compile it as C++ with no issue:
x86_64-w64-mingw32-g++ vol.cpp -lole32
However if I try to compile it as C:
x86_64-w64-mingw32-gcc vol.c -lole32
I get errors such as:
error: ‘IAudioEndpointVolume’ has no member named ‘GetMasterVolumeLevelScalar’
This program does not seem to be particularly “C++”, so what is causing the
problem? Also, can I change something so that it compiles as C?

Answer 1

This seems to do it:
#include <stdio.h>
#include <initguid.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>
#include <math.h>
int main() {
IAudioEndpointVolume *wh;
IMMDevice *ya;
IMMDeviceEnumerator *xr;
CoInitialize(0);
CoCreateInstance(&CLSID_MMDeviceEnumerator, 0, CLSCTX_INPROC_SERVER,
&IID_IMMDeviceEnumerator, (void**)&xr);
xr->lpVtbl->GetDefaultAudioEndpoint(xr, eRender, eConsole, &ya);
ya->lpVtbl->Activate(ya, &IID_IAudioEndpointVolume, CLSCTX_ALL,
0, (void**)&wh);
float zu;
wh->lpVtbl->GetMasterVolumeLevelScalar(wh, &zu);
printf("%d\n", (int) round(100 * zu));
}
Changes:
#include <initguid.h>
&CLSID_MMDeviceEnumerator instead of __uuidof(MMDeviceEnumerator)
lpVtbl->GetDefaultAudioEndpoint instead of GetDefaultAudioEndpoint
Source