Question

If I have the following C++ classes:

class FileIOBase
{
  //regular file operations
  //
  //virtual fstream / ifstream / ofstream getStream();  ???
  //
  bool open(const std::string &path);
  bool isOpen() const;
  void close();
  ...
};

class InputFile : FileIOBase
{
  size_t read(...);
  ifstream getStream();
};

class OutputFile : FileIOBase
{
  size_t write(...);
  ofstream getStream();
};

class InputOutputFile : virtual InputFile, virtual OutputFile
{
  fstream getStream();
};

The classes just encapsulate standard in, out, in/out file streams and their operations.

Is there any way to make getStream() part of the interface and move it into FileIOBase?

Answer 1

I think you mean to make those return values references instead of values. If that is the case, you can have getStream in the base class return a ios&, then you can have the specific functions return fstream&, ifstream& and ofstream&s because they are covariant with ios&:

class FileIOBase
{
  ...
  bool open(const std::string &path);
  bool isOpen() const;
  void close();

  virtual ios& getStream() = 0;
  ...
};

class InputFile : FileIOBase
{
  size_t read(...);
  ifstream& getStream();
};

class OutputFile : FileIOBase
{
  size_t write(...);
  ofstream& getStream();
};

class InputOutputFile : virtual InputFile, virtual OutputFile
{
  fstream& getStream();
};