Chapter 15, Problem 9PC

File Filter

A file filter reads an input file, transforms it in some way, and writes the results to an output File. Write an abstract file filter class that defines a pure virtual function for transforming a character. Create one derived class of your file filter class that performs encryption, another that transforms a file to all uppercase, and another that creates an unchanged copy of the original file. The class should have the following member function:

void doFilterfifstream &in, ofstream &out)

This function should be called to perform the actual filtering. The member function for transforming a single character should have the prototype:

char transformfehar ch)

The encryption class should have a constructor that takes an integer as an argument and uses it as the encryption key.