The following example returns the group memberships in the current process’s access token

#include "stdafx.h"
#include <Windows.h>
#include <Iads.h>
#include <AdsHlp.h>

int _tmain(int argc, _TCHAR* argv[])
{
	DWORD i, dwSize;
	HANDLE hToken;
	PTOKEN_GROUPS pGroupInfo;
	PTOKEN_USER pUserInfo = NULL;
    HRESULT hr;

    hr = CoInitialize(NULL);
    if(SUCCEEDED(hr))
    {
		// Open a handle to the access token for the calling process.
		if (OpenProcessToken (GetCurrentProcess(), TOKEN_QUERY, &hToken))
		{
			dwSize = 0;
			GetTokenInformation (hToken, TokenUser, NULL, dwSize, &dwSize);
			if (pUserInfo = (PTOKEN_USER) GlobalAlloc (GPTR, dwSize))
			{
				// Call GetTokenInformation again to get the group information.
				if (!GetTokenInformation (hToken, TokenUser, pUserInfo, dwSize, &dwSize)) 
				{
					GlobalFree (pUserInfo);
					pUserInfo = NULL;
				}
			}
			dwSize = 0;
			GetTokenInformation (hToken, TokenGroups, NULL, dwSize, &dwSize);
			if (pGroupInfo = (PTOKEN_GROUPS) GlobalAlloc (GPTR, dwSize))
			{
				if (GetTokenInformation (hToken, TokenGroups, pGroupInfo, dwSize, &dwSize)) 
				{
					static WCHAR szName[1024], szDomain[1024];

					for (i=0; i < pGroupInfo->GroupCount; i++)
					{
						if (pGroupInfo->Groups[i].Attributes & SE_GROUP_ENABLED)
						{
							BOOL bEqual = FALSE;
							if (EqualDomainSid (pUserInfo->User.Sid, pGroupInfo->Groups[i].Sid, &bEqual)) 
							{
								if (bEqual)
								{
									DWORD	dwName, dwDomain;
									SID_NAME_USE SidNameUse;
									dwName = 1024;
									dwDomain = 1024;
									if (LookupAccountSid (NULL, pGroupInfo->Groups[i].Sid, szName, &dwName, szDomain, &dwDomain, &SidNameUse))
										wprintf(L"%s\n",szName);
								}
							}
						}
					}
				}
				GlobalFree (pGroupInfo);
			}
			if (pUserInfo != NULL) 
				GlobalFree (pUserInfo);
			
			//Close the access token handle
			CloseHandle (hToken);
		}
	}
    CoUninitialize();
    return 0;
}