从Windows系统服务获取活动用户的注册表信息

首先，对“活动用户”的定义是，当前拥有桌面的用户。对于Windows XP及其以后的系统，即使是可以多个用户同时登录了，拥有桌面的也仅仅只有一个。
如果系统级服务调用Windows API来获取注册表键值的时候，直接以HKEY_CURRENT_USER为参数，则取到的并不是活动用户的注册表信息，而是系统用户的注册表信息，即，位于HKEY_LOCAL_MACHINE之下的。那么如何以系统服务的身份获取活动用户（真正的HKEY_CURRENT_USER）之下的注册表信息呢？主要有以下这么几步：

1. 系统服务程序调用 WTSGetActiveConsoleSessionId() 以获取当前活动用户的sessionId.
2. 以此sessionId为参数，调用 WTSQueryUserToken() 以获取当前活动用户的 hUserToken.
3. 以此hUserToken为参数，调用 DuplicateTokenEx() 以复制一个token，如hFakeToken.
4. 以此hFakeToken为参数，调用 ImpersonateLoggedOnUser() 以模拟活动用户登录的环境.
5. 调用 RegOpenCurrentUser() 以打开活动用户的 HKEY_CURRENT_USER.
6. 调用 RegOpenKeyEx() 以获取指定位置的注册表键值.

以QT和Windows API来实现的代码如下：

void GetUserRegistryFromSystemService()
{
#ifdef Q_OS_WIN

    DWORD sessionId = WTSGetActiveConsoleSessionId();
    qInfo() << "Session ID = " << sessionId;

    wchar_t * ppUserName[100];
    DWORD sizeOfUserName;
    WTSQuerySessionInformation(WTS_CURRENT_SERVER_HANDLE, sessionId, WTSUserName, ppUserName, &sizeOfUserName);
    qInfo() << "Windows User Name = " << QString::fromWCharArray(*ppUserName);

    std::wstring strValueOfBinDir = L"Unknown Value";
    LONG regOpenResult = ERROR_SUCCESS;

    HANDLE hUserToken = NULL;
    HANDLE hFakeToken = NULL;

    if (WTSQueryUserToken(sessionId, &hUserToken))
    {
         if (DuplicateTokenEx(hUserToken, TOKEN_ASSIGN_PRIMARY | TOKEN_ALL_ACCESS, 0, SecurityImpersonation, TokenPrimary, &hFakeToken) == TRUE)
         {
            if (ImpersonateLoggedOnUser(hFakeToken))
            {
                HKEY hKey;

                regOpenResult = RegOpenCurrentUser(KEY_READ, &hKey);
                if (regOpenResult != ERROR_SUCCESS)
                {
                    qCritical() << "Failed to call RegOpenCurrentUser(), Error is " << regOpenResult;
                }

                HKEY hSubKey;

                RegOpenKeyEx(hKey,
                             TEXT("Software\\Baidu\\BaiduYunGuanjia"),
                             0,
                             KEY_READ,
                             &hSubKey);
                GetStringRegKey(hSubKey, TEXT("installDir"), strValueOfBinDir, TEXT("Unknown"));

                RevertToSelf();
            }
            else
            {
                qCritical() << "Failed to ImpersonateLoggedOnUser...";
            }
            CloseHandle(hFakeToken);
        }
        else
        {
            qCritical() << "Failed to call DuplicateTokenEx...";
        }
        CloseHandle(hUserToken);
    }
    else
    {
        qCritical() << "Failed to get the user token of session " << sessionId;
    }

    qInfo() << "The value of Registry is " << QString::fromWCharArray( strValueOfBinDir.c_str() );

#endif
}

最后，取注册表信息一些方法：

HKEY hKey;
LONG lRes = RegOpenKeyExW(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Perl", 0, KEY_READ, &hKey);
bool bExistsAndSuccess (lRes == ERROR_SUCCESS);
bool bDoesNotExistsSpecifically (lRes == ERROR_FILE_NOT_FOUND);

std::wstring strValueOfBinDir;
std::wstring strKeyDefaultValue;
GetStringRegKey(hKey, L"BinDir", strValueOfBinDir, L"bad");
GetStringRegKey(hKey, L"", strKeyDefaultValue, L"bad");

LONG GetStringRegKey(HKEY hKey, const std::wstring &strValueName, std::wstring &strValue, const std::wstring &strDefaultValue)
{
    strValue = strDefaultValue;
    WCHAR szBuffer[512];
    DWORD dwBufferSize = sizeof(szBuffer);
    ULONG nError;
    nError = RegQueryValueExW(hKey, strValueName.c_str(), 0, NULL, (LPBYTE)szBuffer, &dwBufferSize);
    if (ERROR_SUCCESS == nError)
    {
        strValue = szBuffer;
    }
    return nError;
}

LONG GetDWORDRegKey(HKEY hKey, const std::wstring &strValueName, DWORD &nValue, DWORD nDefaultValue)
{
    nValue = nDefaultValue;
    DWORD dwBufferSize(sizeof(DWORD));
    DWORD nResult(0);
    LONG nError = ::RegQueryValueExW(hKey,
        strValueName.c_str(),
        0,
        NULL,
        reinterpret_cast(&nResult),
        &dwBufferSize);
    if (ERROR_SUCCESS == nError)
    {
        nValue = nResult;
    }
    return nError;
}


LONG GetBoolRegKey(HKEY hKey, const std::wstring &strValueName, bool &bValue, bool bDefaultValue)
{
    DWORD nDefValue((bDefaultValue) ? 1 : 0);
    DWORD nResult(nDefValue);
    LONG nError = GetDWORDRegKey(hKey, strValueName.c_str(), nResult, nDefValue);
    if (ERROR_SUCCESS == nError)
    {
        bValue = (nResult != 0) ? true : false;
    }
    return nError;
}