C++ inheritance design: avoid member duplication

Question

Let's assume that one has two C++ classes that support read-only and write-only operations on a file descriptor respectively.

class ReadFd {
 public:
  ssize_t read( /* */ ) {
    // read from file_descriptor_
  }
 protected:
  int file_descriptor_;
};

class WriteFd {
 public:
  ssize_t write(/* */) {
    // write to file_descriptor_
  }
 protected:
  int file_descriptor_;
};

Now suppose one would like to define a class ReadWriteFd that supports both read and write operations.

My question is how to design such read-write class to avoid code duplication?

I cannot inherit from both ReadFd and WriteFd because obviously I need just one file_descriptor_. The real situation that I encountered a bit more complicated but the concept here reflects it rather close.

Answer 1

Add a third class, base to both ReadFd and WriteFd, whose only purpose is to contain the descriptor variable (and possibly other things common to both reading and writing).