C#接收C++dll可变长字节或者字符指针char*

extern "C"      __declspec(dllexport)   char  *  GetFileByteArray(wchar_t * BinfilePath, wchar_t *BinfileName,int indexFile, int * length)
 {

       
     char *chBinfilePath= nullptr, *chBinfileName = nullptr;
     wchar_tTranstoChar(BinfilePath, &chBinfilePath);
     wchar_tTranstoChar(BinfileName, &chBinfileName);

     char a[] = "13345zh中文 hello";
        //前提条件需要 返回变长的指针
     int  fileCount = sizeof(a);
        
     char  *att = new char[fileCount];
     memcpy(att, a, fileCount);

     *length = fileCount-1; // C#获得长度 

     free(chBinfilePath);
     free(chBinfileName);
    
     return  att;// C# 获得指针
    
 }

        [DllImport("BASECORELIBRARY.dll", CharSet = CharSet.Unicode, CallingCOnvention= CallingConvention.StdCall)]
        public static extern IntPtr GetFileByteArray(string BinfilePath, string BinfileName, int indexFile,ref  int length);




 int length = 0;
          
            IntPtr piBuf = InvokeDLL.GetFileByteArray(newFilePath, toBinName, 0, ref length);
            
            byte[] arrayBuf = new byte[length];
            Marshal.Copy(piBuf,arrayBuf,0, length);

            string st=  Encoding.Default.GetString(arrayBuf);
            Console.WriteLine(st);