C++ Programming Consider the following scheme for encrypting a text file. The or
ID: 3871858 • Letter: C
Question
C++ Programming
Consider the following scheme for encrypting a text file. The original file is split into two new files. One of the two new files will contain all the characters in the original file in odd position and the other new file will contain all the characters in the original file in even position. That is, the first file would contain the first, third, fifth, seventh, etc. characters from the original and the other file would contain the second, fourth, sixth, etc. characters. For example, if the original file contained the text: That's all folks! then the first file would contain: Ta' l ok! and the second file would contain: htsalfls
For this assignment you are to implement the encryption and decryption functions for such a scheme and write a driver program to test them.
The first function
void split(char sourceFile[], char destFile1[], char destFile2[]);
should:
1. Open sourceFile as an input file stream,
2. Open destFile1 and destFile2 as output file streams
3. Read each character from sourceFile and
4. If it's an even numbered character (starting at 0), place it in destFile1
5. Else place it in destFile2
6. Close the files
The second function
void merge(char sourceFile1[], char sourceFile2[], char destFile[]);
should reverse the previous process.
To test these two functions, your main function should do the following:
1) Ask the user for the name of the input file.
2) Ask the user for the names of the two half files.
3) Call the split function with the filenames as parameters.
4) Ask the user for the name for the recombined file.
5) Call the merge function with the appropriate filenames as parameters.
Your program should also:
Give detailed directions and warnings to the user.
Be readable with appropriate documentation and formatting.
Explanation / Answer
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
using namespace std;
// -- Function Headers --
//Pre: 'sourceFile' is location of the file to encrypt.
// 'destFile1' and 'destFile2' are the locations of the files to store the encrypted data.
//Post: Files 'destFile1' and 'destFile2' have been created/overwritten with the encrypted data.
void split(const char sourceFile[], const char destFile1[], const char destFile2[]);
//Pre: 'sourceFile1' and 'sourceFile2' are the location of the encrypted data.
// 'destFile' is the location used to store the decrypted file.
//Post: 'destFile' has been created/overwritten with the decrypted data.
void merge(const char sourceFile1[], const char sourceFile2[], const char destFile[]);
// * Helper Functions *
//Pre: Location/name of the file to validate.
//Post: If input file doesn't exist or we are denied permissions to access it, an error message is returned to the user
// and the program exits.
void validateInFile(const char fileName[]);
//Pre: 'iStream' is the memory address of the ifstream to open.
// 'fileName' is the location/name of the file to open the stream with.
//Post: 'iStream' has been created OR opening of stream failed and program has exited.
void createInStream(ifstream &iStream, const char fileName[]);
//Pre: Location/name of the file to validate.
//Post: Checks if the output file exists. If it does, a warning it prompted to the user.
// if user opts to quit, the program exits.
void validateOutFile(const char fileName[]);
//Pre: 'oStream' is the memory address of the ofstream to open.
// 'fileName' is the location/name of the file to open the stream with.
//Post: 'oStream' has been created OR opening of stream failed and program has exited.
void createOutStream(ofstream &oStream, const char fileName[]);
// -- Program entry point --
int main()
{
int input;
//Will be used to hold the locations/names of the files to be used in the split/merge functions.
string fileName[3];
cout << "This program can be used for file encryption/decryption ";
cout << "The program can encrypt a file by splitting it's ";
cout << " characters into two seperate files. ";
cout << "The program can also decrypt your encrypted files ";
cout << " by re-attaching them back into one file. ";
cout << "What would you like to do? ";
cout << "1. Encrypt a file ";
cout << "2. Decrypt a set of files ";
cout << "3. Exit ";
cout << "Your input: ";
if (!(cin >> input))
{
cout << "Invalid input. Program will now exit ";
return 0;
}
switch (input)
{
//user has opted to encrypt an existing file.
case 1:
cout << " Enter the name of the source file to encrypt: ";
cin >> fileName[0];
validateInFile(fileName[0].c_str());
cout << "Enter the name of the first destination file for output: ";
cin >> fileName[1];
//Warn user if output already exists and that it will be overwritten. If user opts to quit, program will exit.
validateOutFile(fileName[1].c_str());
cout << "Enter the name of the second destination file for output: ";
cin >> fileName[2];
validateOutFile(fileName[2].c_str());
split(fileName[0].c_str(), fileName[1].c_str(), fileName[2].c_str());
break;
//User has opted to decrypt an already encrypted file.
case 2:
cout << " Ensure the source files are in the correct order, or decryption will fail. ";
cout << "Enter the name of the first source file to decrypt: ";
cin >> fileName[0];
validateInFile(fileName[0].c_str());
cout << "Enter the name of the second source file to decrypt: ";
cin >> fileName[1];
validateInFile(fileName[1].c_str());
cout << "Enter the name of the destination file for output: ";
cin >> fileName[2];
validateOutFile(fileName[2].c_str());
merge(fileName[0].c_str(), fileName[1].c_str(), fileName[2].c_str());
break;
//User has opted to exit program.
case 3:
return 0;
default:
cout << "Option " << input << " is non-existant. Program will now exit ";
return 0;
}
return 0;
}
void split(const char sourceFile[], const char destFile1[], const char destFile2[])
{
ifstream inStream;
createInStream(inStream, sourceFile);
ofstream outStream1;
createOutStream(outStream1, destFile1);
ofstream outStream2;
createOutStream(outStream2, destFile2);
//charCount is used to determine odd/even characters which will determine which stream the
//input character will be written to.
int charCount = 1;
char currentRead;
while (inStream.get(currentRead))
{
if ((charCount++) % 2 != 0)
outStream1.put(currentRead);
else
outStream2.put(currentRead);
}
cout << " "" << sourceFile << "" has been successfully encrypted and ";
cout << "Files "" << destFile1 << "" and "" << destFile2 << "" have been successfully created. ";
inStream.close();
outStream1.close();
outStream2.close();
}
void merge(const char sourceFile1[], const char sourceFile2[], const char destFile[])
{
ifstream inStream1;
createInStream(inStream1, sourceFile1);
ifstream inStream2;
createInStream(inStream2, sourceFile2);
ofstream outStream;
createOutStream(outStream, destFile);
char inChar1, inChar2;
while (inStream1.get(inChar1))
{
outStream.put(inChar1);
//Since second stream may possibly be one character shorter than the first stream,
//do a seperate check to ensure we are still getting a character from it as well.
if (inStream2.get(inChar2))
outStream.put(inChar2);
}
cout << " Files "" << sourceFile1 << "" and "" << sourceFile2 << "" have been successfully decrypted and ";
cout << """ << destFile << "" has been successfully created. ";
inStream1.close();
inStream2.close();
outStream.close();
}
void validateInFile(const char fileName[])
{
ifstream stream;
//create the stream. if stream creation was successful, the file in turn is valid.
//if stream fails, file is invalid and program will exit.
createInStream(stream, fileName);
stream.close();
}
void createInStream(ifstream &iStream, const char fileName[])
{
iStream.open(fileName);
if (!iStream.good())
{
cout << "File "" << fileName << "" doesn't exist or has invalid permissions. ";
cout << "Program will now exit. ";
exit(EXIT_FAILURE);
}
}
void validateOutFile(const char fileName[])
{
ifstream stream(fileName);
if (stream.good())
{
string userInput;
cout << "File "" << fileName << "" already exists. ";
cout << "If you continue, this file will be overwritten. ";
cout << "Do you wish to continue (y/n)? ";
cin >> userInput;
if (userInput == "y")
{
stream.close();
return;
}
else
exit(EXIT_SUCCESS);
}
stream.close();
}
void createOutStream(ofstream &oStream, const char fileName[])
{
oStream.open(fileName);
if (!oStream.good())
{
cout << "Error creating output file"" << fileName << "". ";
cout << "Program will now exit. ";
exit(EXIT_FAILURE);
}
}
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