求教：C#调用C++写的DLL 关于 unsigned char*的声明问题

1、SDK.H 中有声明以下函数//回调
typedef bool (CALLBACK *DataCallBack)(int index, int type, BYTE *pData, int len, int param1, int param2);
//设置回调
DLL_EXPORT int WAPA_IPC_SetDataCallBack(DataCallBack fData);
//连接摄像机
DLL_EXPORT int WAPA_IPC_Login(char *sCameraIp, int dataFormat);
//初始化解码器
DLL_EXPORT int WAPA_IPC_InitDec(int index, int width, int height, int encodeFormat, int dataFormat);
//解码
DLL_EXPORT int WAPA_IPC_Dec(int index, unsigned char *istream, int istream_size, unsigned char *ostream);
//拍照并保存
DLL_EXPORT int WAPA_IPC_OnPhoto(int index, unsigned char* pImageBuf, int width, int height, int dataFormat, char* fileName = NULL);
2、我在C#中声明如下publlic class WAPAMethods
{
//回调
public unsafe delegate bool DataCallBack(int index, int mode, byte* data, int len, int w, int h);
        /// <summary>
        /// 设置事件回调函数
        /// </summary>
        /// <param name="fEvent"></param>
        /// <returns></returns>
        [DllImport(WAPA_DLL, EntryPoint = "WAPA_IPC_SetEventCallBack", CallingConvention = CallingConvention.Cdecl)]
        public static extern int WAPA_IPC_SetEventCallBack(EventCallBack fEvent);
        /// <summary>
        /// 连接到录像机
        /// </summary>
        /// <param name="sCameraIp">IP地址</param>
        /// <param name="dataFormat">0：解码前数据；1：YUYV格式数据；2：RGB格式数据</param>
        /// <returns></returns>
        [DllImport(WAPA_DLL, EntryPoint = "WAPA_IPC_Login", CallingConvention = CallingConvention.Cdecl)]
        public static extern int WAPA_IPC_Login(string sCameraIp, int dataFormat);
        /// <summary>
        /// 初始化解码器
        /// </summary>
        /// <param name="index"></param>
        /// <param name="width">图像宽</param>
        /// <param name="height">图像高</param>
        /// <param name="encodeFormat">压缩数据格式 264：H.264；265：MPEG4</param>
        /// <param name="dataFormat">输出的数据格式 1：YUYV；2：RGB</param>
        /// <returns></returns>
        [DllImport(WAPA_DLL, EntryPoint = "WAPA_IPC_InitDec", CallingConvention = CallingConvention.Cdecl)]
        public static extern int WAPA_IPC_InitDec(int index, int width, int height, int encodeFormat, int dataFormat);
        /// <summary>
        /// 解码
        /// </summary>
        /// <param name="index">解码器索引号</param>
        /// <param name="istream">编码数据</param>
        /// <param name="istream_size">编码的数据大小</param>
        /// <param name="ostream">解码后的数据</param>
        /// <returns></returns>
        [DllImport(WAPA_DLL, EntryPoint = "WAPA_IPC_Dec", CallingConvention = CallingConvention.Cdecl)]
        //DLL_EXPORT int WAPA_IPC_Dec(int index, unsigned char *istream, int istream_size, unsigned char *ostream);
        public static extern unsafe int WAPA_IPC_Dec(int index, byte* istream, int istream_size, byte* ostream);
        //拍照. pImageBuf:返回的数据. dataFormat:YUYV,RGB
        [DllImport(WAPA_DLL, EntryPoint = "WAPA_IPC_OnPhoto", CallingConvention = CallingConvention.Cdecl)]
        public static extern unsafe int WAPA_IPC_OnPhoto(int index,byte* pImageBuf, int width, int height, int dataFormat, string fileName = null);}3、在Winform中调用public partial class Form1 : Form
{
        private WAPAMethods.DataCallBack _dataCallBack;
        private unsafe byte* frameBuf;
        private unsafe void Form1_Load(object sender, EventArgs e)
        {
            _dataCallBack = DataOnReceived;
            WAPAMethods.WAPA_IPC_SetDataCallBack(_dataCallBack);
            Reconnected();
        }
        public void Reconnected()
        {
            //连接摄像机
            _cameraIndex = WAPAMethods.WAPA_IPC_Login(_ip,2);
            if(_cameraIndex==206)return;
            //连接成功后初始化解码器
            WAPAMethods.WAPA_IPC_InitDec(_cameraIndex, 1280, 960, 264, 2);
        }
        private unsafe bool DataOnReceived(int index, int mode, byte* data, int len, int w, int h)
        {
            //解码
            var ret = WAPAMethods.WAPA_IPC_Dec(index,data, len, frameBuf);
            //拍照
            ret = WAPAMethods.WAPA_IPC_OnPhoto(index, frameBuf, w, h, 2, null);
            return true;
        }
}
问题来了：frameBuf应该是解码后的视频指针地址，可现在神马也没有，断点显示是0x000000，请问这个unsigned char *的参数要怎么声明？C++C#DLL