add virtual destructor to iseekstream

include/rabit/io.h

@@ -19,6 +19,8 @@ namespace utils {
 /*! \brief interface of i/o stream that support seek */
 class ISeekStream: public IStream {
  public:
+  // virtual destructor
+  virtual ~ISeekStream(void) {}
   /*! \brief seek to certain position of the file */
   virtual void Seek(size_t pos) = 0;
   /*! \brief tell the position of the stream */

rabit-learn/io/hdfs-inl.h

@@ -23,7 +23,7 @@ class HDFSStream : public utils::ISeekStream {
              bool disconnect_when_done)
       : fs_(fs), at_end_(false),
         disconnect_when_done_(disconnect_when_done) {
-    int flag;
+    int flag = 0;
     if (!strcmp(mode, "r")) {
       flag = O_RDONLY;
     } else if (!strcmp(mode, "w"))  {