Question

A file filter reads an input file, transforms it in some way, and writes the results to an out-put 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 doFilter(ifstream &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 transform(char ch)

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

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

#include<iostream>

#include<fstream>

using namespace std;

//abstract Filter class

class Filter{

                public:

                //defining pure virtual function

                virtual void doFilter(ifstream &in, ofstream &out)=0;

};

//EncryptionFilter class

class EncryptionFilter: public Filter{

                private:

                //encryption key

                int key;

                public:

                //contstructor taking encryption key

                EncryptionFilter(int k){

                                key=k;

                }

                //method to apply filter

                void doFilter(ifstream &in, ofstream &out){

                                char ch;

                                //reading all characters one by one until eof

                                while(in.get(ch)){

                                               //transforming ch

                                               ch=transform(ch);

                                               //writing to output stream

                                               out<<ch;

                                }

                }

                //method to transform a character

                char transform(char ch){

                                //checking if ch is lower case

                                if(ch>='a' && ch<='z'){

                                               //adding key value

                                               ch+=key;

                                               //wrapping around if ch >'z'

                                               if(ch>'z'){

                                                               int index=ch-'z';

                                                               ch='a'+index;

                                               }

                                }

                                //doing the same for upper case

                                else if(ch>='A' && ch<='Z'){

                                               ch+=key;

                                               if(ch>'Z'){

                                                               int index=ch-'Z';

                                                               ch='A'+index;

                                               }

                                }

                                return ch;

                }

};

//UpperCaseFilter class

class UpperCaseFilter: public Filter{

                private:

                int key;

                public:

                UpperCaseFilter(){

                               

                }

               

                void doFilter(ifstream &in, ofstream &out){

                                char ch;

                                while(in.get(ch)){

                                               ch=transform(ch);

                                               out<<ch;

                                }

                }

                char transform(char ch){

                                //if ch is lower case, converting to upper case

                                if(ch>='a' && ch<='z'){

                                               int index=ch-'a';

                                               ch='A'+index;

                                }

                                return ch;

                }

};

//UnchangedFilter class

class UnchangedFilter: public Filter{

                private:

                int key;

                public:

                UnchangedFilter(){

                               

                }

               

                void doFilter(ifstream &in, ofstream &out){

                                char ch;

                                while(in.get(ch)){

                                               ch=transform(ch);

                                               out<<ch;

                                }

                }

                char transform(char ch){

                                //returning ch with no changes

                                return ch;

                }

};

int main(){

                //creating objects for each Filter

                EncryptionFilter encFilter(3);

                UpperCaseFilter upFilter;

                UnchangedFilter unchangedFilter;

                //asking user to enter an input file name

                cout<<"Enter input file name: "<<endl;

                string filename;

                cin>>filename;

                //opening input file, verifying if it is opened correctly

                ifstream inFile1(filename.c_str());

                if(!inFile1){

                                cout<<"Input file not found!"<<endl;

                                return 0;

                }

               

                //opening three output files for writing the filtered results

                ofstream outFile1("output1.txt");

                ofstream outFile2("output2.txt");

                ofstream outFile3("output3.txt");

               

                //applying each filter, storing in each output file

                encFilter.doFilter(inFile1,outFile1);          

                //resetting ifstream pointer to point to the beginning of file

                inFile1.close();

                inFile1.clear();

                inFile1.open(filename);

               

                upFilter.doFilter(inFile1,outFile2);

                inFile1.close();

                inFile1.clear();

                inFile1.open(filename);

                unchangedFilter.doFilter(inFile1,outFile3);

                inFile1.close();

                inFile1.clear();

                //closing each file, saving output

                outFile1.close();

                outFile2.close();

                outFile3.close();

                return 0;

}

/*OUTPUT*/

Enter input file name:

input.txt

//input.txt

some text

in this file

some

more text

following

some text

in this file

some

more text

following

//output1.txt

vrph whbw

lq wklv iloh

vrph

pruh whbw

iroorzlqj

vrph whbw

lq wklv iloh

vrph

pruh whbw

iroorzlqj

//output2.txt

SOME TEXT

IN THIS FILE

SOME

MORE TEXT

FOLLOWING

SOME TEXT

IN THIS FILE

SOME

MORE TEXT

FOLLOWING

//output3.txt

some text

in this file

some

more text

following

some text

in this file

some

more text

following