C++ File handling: Decrypting the contents of a text file

C++ File handling: Exercise-13 with Solution

Write a C++ program to decrypt the contents of a text file encrypted using the above algorithm.

Sample Solution:

C Code:

#include <iostream>   // Including the input/output stream library
#include <fstream>    // Including the file stream library
#include <string>     // Including the string handling library

// Function to display the content of a file
void displayFileContent(const std::string & filename) {
  std::ifstream file(filename); // Open file with given filename for reading
  std::string line; // Declare a string to store each line of text

  if (file.is_open()) { // Check if the file was successfully opened
    std::cout << "File content:" << std::endl; // Displaying a message indicating file content
    while (std::getline(file, line)) { // Read each line from the file
      std::cout << line << std::endl; // Display each line of the file
    }
    file.close(); // Close the file
  } else {
    std::cout << "Failed to open the file." << std::endl; // Display an error message if file opening failed
  }
}

// Function to decrypt a file using a simple algorithm (decrementing ASCII values)
void decryptFile(const std::string & inputFile, const std::string & outputFile) {
  std::ifstream input(inputFile); // Open input file for reading
  std::ofstream output(outputFile); // Open or create output file for writing

  if (input.is_open() && output.is_open()) { // Check if both files were successfully opened
    char ch; // Declare a character variable to read characters from the input file

    while (input.get(ch)) { // Loop through each character in the input file
      ch--; // Simple decryption algorithm: Decrement ASCII value by 1
      output.put(ch); // Write the decrypted character to the output file
    }

    input.close(); // Close the input file
    output.close(); // Close the output file

    std::cout << "File decrypted successfully.\n" << std::endl; // Display a success message
  } else {
    std::cout << "Failed to open the files.\n" << std::endl; // Display an error message if file opening failed
  }
}

int main() {
  std::string inputFile = "encrypted_test.txt"; // Input file (encrypted)
  displayFileContent("encrypted_test.txt"); // Display content of "encrypted_test.txt"
  std::cout << std::endl; // Output a newline for formatting

  std::string outputFile = "decrypted_test.txt"; // Output file (decrypted)
  decryptFile(inputFile, outputFile); // Decrypt "encrypted_test.txt" and write to "decrypted_test.txt"
  displayFileContent("decrypted_test.txt"); // Display content of "decrypted_test.txt"
  std::cout << std::endl; // Output a newline for formatting

  return 0; // Return 0 to indicate successful execution
}

Sample Output:

File content:
D,,!jt!b!ijhi.mfwfm-!hfofsbm.qvsqptf!qsphsbnnjoh!mbohvbhf!dsfbufe!cz!Ebojti!dpnqvufs!tdjfoujtu!Ckbsof!Tuspvtusvq/!♂Gjstu!sfmfbtfe!jo!2:96!bt!bo!fyufotjpo!pg!uif!D!qsphsbnnjoh!mbohvbhf-!ju!ibt!tjodf!fyqboefe!tjhojgjdboumz!pwfs!ujnf/!♂Npefso!D,,!dvssfoumz!ibt!pckfdu.psjfoufe-!hfofsjd-!boe!gvodujpobm!gfbuvsft-!jo!beejujpo!up!gbdjmjujft!gps!mpx.mfwfm!nfnpsz!nbojqvmbujpo/♂Ju!jt!bmnptu!bmxbzt!jnqmfnfoufe!jo!b!dpnqjmfe!mbohvbhf/♂Nboz!wfoepst!qspwjef!D,,!dpnqjmfst-!jodmvejoh!uif!Gsff!Tpguxbsf!Gpvoebujpo-!MMWN-!Njdsptpgu-!Joufm-!Fncbsdbefsp-!Psbdmf-!boe!JCN/

File decrypted successfully.

File content:
C++ is a high-level, general-purpose programming language created by Danish computer scientist Bjarne Stroustrup.
First released in 1985 as an extension of the C programming language, it has since expanded significantly over time.
Modern C++ currently has object-oriented, generic, and functional features, in addition to facilities for low-level memory manipulation.
It is almost always implemented in a compiled language.
Many vendors provide C++ compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, Embarcadero, Oracle, and IBM.

Explanation:

In the above exercise,

• The function decryptFile() takes two parameters: inputFile (the name of the input file to decrypt) and outputFile (the name of the output file to store the decrypted content).
• The program opens the input file using std::ifstream and the output file using std::ofstream.
• Next, it reads each character from the input file using std::ifstream::get and applies a simple decryption algorithm by decrementing the ASCII value of each character by 1.
• The decrypted character is written to the output file using std::ofstream::put.
• Both the input and output files are closed after the entire file has been decrypted.

Note: Content of a file is displayed using displayFileContent("filename.txt").

Flowchart:

CPP Code Editor:

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