C++ File handling: Sort text file lines alphabetically

Last update on December 20 2024 12:29:16 (UTC/GMT +8 hours)

Write a C++ program to sort the lines of a text file in alphabetical order.

Sample Solution:

C Code:

#include <iostream>   // Including the input/output stream library
#include <fstream>    // Including the file stream library
#include <vector>     // Including the vector container
#include <algorithm>  // Including algorithms like 'sort'
#include <iterator>   // Including iterator operations

// 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
  }
}

int main() {
  std::ifstream inputFile("test1.txt");  // Open the input file named "test1.txt" for reading
  displayFileContent("test1.txt");  // Display content of "test1.txt"
  std::ofstream outputFile("sorted_test1.txt");  // Create or overwrite the output file named "sorted_test1.txt" for writing

  if (inputFile.is_open() && outputFile.is_open()) {  // Check if both input and output files were successfully opened
    std::vector<std::string> lines;  // Vector to store the lines of the file
    std::string line;  // Declare a string variable to store each line of text

    while (std::getline(inputFile, line)) {  // Read each line from the input file and store it in the vector
      lines.push_back(line);  // Push each line to the vector
    }

    std::sort(lines.begin(), lines.end());  // Sort the lines in alphabetical order

    std::copy(lines.begin(), lines.end(), std::ostream_iterator<std::string>(outputFile, "\n"));  // Write the sorted lines to the output file

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

    std::cout << "\nLines sorted successfully.\n" << std::endl;  // Display a success message
    displayFileContent("sorted_test1.txt");  // Display content of "sorted_test1.txt"
  } else {
    std::cout << "\nFailed to open the files." << std::endl;  // Display an error message if file opening failed
  }

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

Sample Output:

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

Lines sorted 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.
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.
Modern C++ currently has object-oriented, generic, and functional features, in addition to facilities for low-level memory manipulation.

Explanation:

In the above exercise -

• Open the input file using std::ifstream and the output file using std::ofstream.
• Use a vector lines to store the input file lines. Read each line from the input file using std::getline() and push it into the vector.
• Use the std::sort() function from the <algorithm> library to sort the lines in alphabetical order.
• Write the sorted lines to the output file using std::copy() and std::ostream_iterator.
• After running the program, the input file lines will be sorted in alphabetical order and written to the output file.

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

Flowchart:

CPP Code Editor:

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