dynamic_cast from ostream to ofstream is causing segmentation fault

In the code below I am trying to create a Logging application which outputs to either cout or to a selected file.

1. I used ostream to hold either a ofstream object or cout.
2. in the Destructor of CLog i want to close the file if ostream object is not cout.

3. but dynamic_cast from ostream to ofstream is causing segmentation fault.
   
   what can be the issue that is causing Segmentation Fault ?
   

   CLog(std::ostream & streamObj = std::cout);
   
   CLog::CLog(std::ostream & streamObj) 
   {
   
   }
   
   CLog::~CLog() 
   {
      if (pStreamObj != NULL && &(std::cout)!= pStreamObj) //if the streamObj is a file stream 
      {
          dynamic_cast<std::ofstream&>(*pStreamObj).close();
   
          delete pStreamObj;
      }
   }