text: #ifndef CL_SACHNGOAI_H_
  #define CL_SACHNGOAI_H_
  
  #include "Sach.h"
  
  class SachNgoai : public SachViet
  {
  public:
  		SachNgoai() : SachViet() {}
  		SachNgoai(
  				const str& _ten,
  				const str& _ma_sach,
  				const str& _tac_gia,
  				const str& _nxb,
  				const str& _gia_sach,
  				const str& _isbn
  		) : SachViet(_ten, _ma_sach, _tac_gia, _nxb, _gia_sach), sISBN(_isbn) {}
  		virtual ~SachNgoai() {}
  
  		//Setters
  		inline str& isbn() { return sISBN; }
  
  		//Getters
  		inline const str& isbn() const { return sISBN; }
  
  		//Read, Write data
  		virtual std::ostream& stream_write(std::ostream& os) const;
  		virtual std::istream& stream_read(std::istream& is);
  		virtual std::ifstream& stream_read(std::ifstream& ifs);
  
  private:
  		str sISBN;
  };
  #endif
  