What's wrong with this GetDefaultAudioEndpoint program? - c++

Question

Here's a very simple program using the function:
#include <windows.h>
#include <tchar.h>
#include <atlstr.h>
#include <mmdeviceapi.h>
#include <devicetopology.h>
#include <functiondiscoverykeys.h>
#include <iostream>
using namespace std;
int main()
{
HRESULT hr;
CComPtr<IMMDeviceEnumerator> pMMDeviceEnumerator;
pMMDeviceEnumerator->GetDefaultAudioEndpoint(eCapture, eMultimedia, 0);
//cout << hr;
return 0;
}
When I try to run this, I get the following error:
Debug Assertion Failed!
Program: ...
File: c:\program files\microsoft visual studio 8\vc\atlmfc\include\atlcomcli.h
Line: 154
Expression: p!=0
What's wrong with this? I'm just now trying to learn how to use this function. Thanks!
EDIT:
I've changed the program to this:
//#include <windows.h>
//#include <tchar.h>
#include <atlstr.h>
#include <mmdeviceapi.h>
//#include <devicetopology.h>
//#include <functiondiscoverykeys.h>
#include <iostream>
using namespace std;
// helper class to CoInitialize/CoUninitialize
class CCoInitialize {
private:
HRESULT m_hr;
public:
CCoInitialize(PVOID pReserved, HRESULT &hr)
: m_hr(E_UNEXPECTED) { hr = m_hr = CoInitialize(pReserved); }
~CCoInitialize() { if (SUCCEEDED(m_hr)) { CoUninitialize(); } }
};
int main()
{
CComPtr<IMMDeviceEnumerator> pMMDeviceEnumerator;
HRESULT hr = pMMDeviceEnumerator.CoCreateInstance(__uuidof(MMDeviceEnumerator));
if (FAILED(hr)) {
cout << "failed" << endl;
return __LINE__;
}
CCoInitialize ci(NULL, hr);
pMMDeviceEnumerator->GetDefaultAudioEndpoint(eCapture, eMultimedia, 0);
//cout << hr;
return 0;
}
When I run it, I get the output of "failed". What's happening?
EDIT:
Alright, now I've changed the code enough to get it running all the way through without any failures. i.e.,
HRESULT hr = S_OK;
cout << hr;
// initialize COM
CCoInitialize ci(NULL, hr);
if (FAILED(hr)) {
cout << "failed1" << endl;
return __LINE__;
}
cout << hr;
// get enumerator
CComPtr<IMMDeviceEnumerator> pMMDeviceEnumerator;
hr = pMMDeviceEnumerator.CoCreateInstance(__uuidof(MMDeviceEnumerator));
if (FAILED(hr)) {
cout << "failed2" << endl;
return __LINE__;
}
cout << hr;
// get default render/capture endpoints
CComPtr<IMMDevice> pRenderEndpoint;
hr = pMMDeviceEnumerator->GetDefaultAudioEndpoint(eRender, eConsole, &pRenderEndpoint);
if (FAILED(hr)) {
cout << "failed3" << endl;
return __LINE__;
}
cout << hr;
return 0;
Some of the trouble I was having earlier with this example (see comments on the answers) was fixed just by removing some of the code. But as I run this new body of the main() function, I get the output "0000", meaning that cout << hr always evaluates to "0". Is this a good thing? What info can I get about the default device now? hr. and hr-> don't really bring up any menus, so I'm kind of in the dark. Thanks!

Answer 1

pMMDeviceEnumerator variable holds a pointer, which is NULL. When you try to call an interface method on this pointer, -> operator checks this nullness and issues an assertion failure.
Windows SDK samples show how to use this function and API, check them under: \Samples\multimedia\audio, e.g. osd sample.
This sample is a Win32-based application that demonstrates the use of the Vista APIs for monitoring the default audio output device and
its current volume setting. The sample is written in C++.
OSD does not run on earlier versions of Windows, including Windows XP, Windows 2000, Windows Me, and Windows 98.
UPD: Things in main one needs to reach the GetDefaultAudioEndpoint API call - Sample: find out if your default audio playback and audio capture devices are on the same hardware.