c#开发的客户端，如何调用c++开发的sdk dll库

//初始化TRTC SDK 
//调用链路：WindowsFormsApp1.exe(c#) -> RTCManager.dll(c#) -> TRTCWrapper.dll(c++) -> liteav.dll(c++，要调用的目标dll)
int nRet = RTCWrapper.InitWrapper();

public static class RTCWrapper
{
        /// <summary>
        /// 初始化TRTC
        /// </summary>
        /// <returns>1成功，0失败</returns>
        [DllImport("TRTCWrapper.dll", EntryPoint = "InitWrapper")]
        public static extern int InitWrapper();
}

//初始化TRTC
extern "C" __declspec(dllexport) int _stdcall InitWrapper();

_declspec(dllexport) int _stdcall InitWrapper()
{
    trtcInstance = TRTCCloudCore::GetInstance();
 
    if (trtcInstance)
    {
        trtcInstance->Init();
        return 1;
    }
    else
        return 0;
}

TRTCCloudCore* TRTCCloudCore::GetInstance()
{
    if (m_instance == NULL) {
        engine_mex.lock();
        if (m_instance == NULL)
        {
            m_instance = new TRTCCloudCore();
        }
        engine_mex.unlock();
    }
    return m_instance;
}
 
TRTCCloudCore::TRTCCloudCore()
{
    trtc_module_ = nullptr;
    if (trtc_module_ != nullptr) return;
 
    HMODULE hmodule = NULL;
    GetModuleHandleEx(
        GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
        L"TRTCModule", &hmodule);
 
    char module_path[MAX_PATH] = { 0 };
    ::GetModuleFileNameA(hmodule, module_path, _countof(module_path));
 
    std::string module_dir = GetPathNoExt(module_path);
    if (module_dir.length() == 0) {
        LINFO(L"TRTC GetModule Path Error");
        return;
    }
 
    std::string module_full_path = module_dir + "liteav.dll";
 
    trtc_module_ =
        ::LoadLibraryExA(module_full_path.c_str(), NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
}

//注册SDK的callback
RTCDelegate rtcDelegate = new RTCDelegate();
RTCWrapper.AddTRTCMsgCallBack(rtcDelegate.rtcCallBack);

enum TRTC_MSG
{
    TRTC_MSG_onEnterRoom = 1,
    TRTC_MSG_onExitRoom,
    TRTC_MSG_onRemoteUserEnterRoom,
    TRTC_MSG_onRemoteUserLeaveRoom,
    TRTC_MSG_onError,
    TRTC_MSG_onWarning
    //TODO 补齐TRTC的回调
};
 
namespace RTCManager
{
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    public delegate void RTCWrapperCallback(int trtcModule, int errCode, [In, MarshalAs(UnmanagedType.LPStr)] string errMsg);
 
 
    public class RTCDelegate
    {
        public RTCWrapperCallback rtcCallBack = null;
 
        public RTCDelegate()
        {
            Setcallback();
        }
 
        private void RTCWrapperCallbackFun(int trtcModule, int errCode, [In, MarshalAs(UnmanagedType.LPStr)] string errMsg)
        {
            TRTC_MSG trtcMsg = (TRTC_MSG)trtcModule;
            switch (trtcMsg)
            {
                case TRTC_MSG.TRTC_MSG_onEnterRoom:
                    break;
                default:
                    break;
 
            }
        }
 
        public void Setcallback()
        {
            rtcCallBack = RTCWrapperCallbackFun;
        }
         
    }
}

/// <summary>
/// 注册TRTC通用回调
/// </summary>
/// <param name="callback">通用回调</param>
/// <returns></returns>
[DllImport("TRTCWrapper.dll", EntryPoint = "AddTRTCMsgCallBack")]
public static extern void AddTRTCMsgCallBack(RTCWrapperCallback callback);

//注册TRTC通用回调
extern "C" __declspec(dllexport) void _stdcall AddTRTCMsgCallBack(TRTCMsgCallback messageCallback);

_declspec(dllexport) void _stdcall AddTRTCMsgCallBack(TRTCMsgCallback messageCallback)
{
    if(trtcInstance)
        trtcInstance->MessageCallBack = messageCallback;
    //else 输出错误日志
}

typedef void(*TRTCMsgCallback)(int trtcModule, int errCode, const wchar_t* errMsg);
 
TRTCMsgCallback MessageCallBack = nullptr;

void TRTCCloudCore::onEnterRoom(int result)
{
    if (MessageCallBack)
        MessageCallBack(TRTC_MSG_onEnterRoom, result, L"");
}

private void button1_Click(object sender, EventArgs e)
{
            IntPtr hwnd = this.Handle;
            RTCWrapper.EnterRoom(0,
                "",
                "",
                0);
            RTCWrapper.StartLocalPreview(hwnd);
            RTCWrapper.StartLocalAudio();
}

[DllImport("TRTCWrapper.dll", EntryPoint = "StartLocalPreview")]
public static extern void StartLocalPreview(IntPtr hwnd);

//开启本地预览
extern "C" __declspec(dllexport) void _stdcall StartLocalPreview(HWND hwnd);

_declspec(dllexport) void _stdcall StartLocalPreview(HWND hwnd)
{
    if (trtcInstance)
        trtcInstance->startPreview(hwnd);
    //else 输出错误日志
}

void TRTCCloudCore::startPreview(HWND hwnd)
{
    if (m_pCloud == nullptr)
        return;
 
    if (m_bStartLocalPreview)
        return;
 
    if (!hwnd)
        return;
 
    m_pCloud->startLocalPreview(hwnd);
    m_bStartLocalPreview = true;
}