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File I/O

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File Input/Output (I/O) is a crucial aspect of programming that allows a program to read from and write to files. This module will cover the basics of file handling in C++, including opening, reading, writing, and closing files.

Key Concepts

  1. File Streams: C++ uses file streams to perform file I/O operations.

    • ifstream: Input file stream for reading files.
    • ofstream: Output file stream for writing files.
    • fstream: File stream capable of both reading and writing.

  2. Opening Files: Files can be opened using the open() method or by passing the file name to the stream's constructor.

  3. Reading from Files: Data can be read from files using various methods like >>, getline(), and read().

  4. Writing to Files: Data can be written to files using the << operator or the write() method.

  5. Closing Files: Always close files using the close() method to free up resources.

Practical Examples

Opening and Closing Files

#include <iostream>
#include <fstream>

int main() {
    std::ifstream inputFile("example.txt"); // Open file for reading
    std::ofstream outputFile("output.txt"); // Open file for writing

    if (!inputFile) {
        std::cerr << "Error opening input file!" << std::endl;
        return 1;
    }

    if (!outputFile) {
        std::cerr << "Error opening output file!" << std::endl;
        return 1;
    }

    // Perform file operations here

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

    return 0;
}

Reading from Files

#include <iostream>
#include <fstream>
#include <string>

int main() {
    std::ifstream inputFile("example.txt");
    std::string line;

    if (!inputFile) {
        std::cerr << "Error opening file!" << std::endl;
        return 1;
    }

    while (std::getline(inputFile, line)) {
        std::cout << line << std::endl; // Print each line to the console
    }

    inputFile.close();
    return 0;
}

Writing to Files

#include <iostream>
#include <fstream>

int main() {
    std::ofstream outputFile("output.txt");

    if (!outputFile) {
        std::cerr << "Error opening file!" << std::endl;
        return 1;
    }

    outputFile << "Hello, World!" << std::endl;
    outputFile << "Writing to a file in C++." << std::endl;

    outputFile.close();
    return 0;
}

Practical Exercises

Exercise 1: Reading and Writing

Task: Write a program that reads from a file named input.txt and writes its contents to a file named output.txt.

Solution:

#include <iostream>
#include <fstream>
#include <string>

int main() {
    std::ifstream inputFile("input.txt");
    std::ofstream outputFile("output.txt");
    std::string line;

    if (!inputFile) {
        std::cerr << "Error opening input file!" << std::endl;
        return 1;
    }

    if (!outputFile) {
        std::cerr << "Error opening output file!" << std::endl;
        return 1;
    }

    while (std::getline(inputFile, line)) {
        outputFile << line << std::endl;
    }

    inputFile.close();
    outputFile.close();
    return 0;
}

Exercise 2: Counting Words

Task: Write a program that reads a file named text.txt and counts the number of words in the file.

Solution:

#include <iostream>
#include <fstream>
#include <string>

int main() {
    std::ifstream inputFile("text.txt");
    std::string word;
    int wordCount = 0;

    if (!inputFile) {
        std::cerr << "Error opening file!" << std::endl;
        return 1;
    }

    while (inputFile >> word) {
        wordCount++;
    }

    std::cout << "Number of words: " << wordCount << std::endl;

    inputFile.close();
    return 0;
}

Common Mistakes and Tips

  • Forgetting to Close Files: Always ensure that files are closed after operations to avoid resource leaks.
  • Checking File Open Status: Always check if the file was successfully opened before performing any operations.
  • Handling File Paths: Be mindful of the file paths, especially when working with relative paths. Ensure the file exists in the specified location.

Conclusion

In this section, we covered the basics of file I/O in C++. You learned how to open, read, write, and close files using file streams. Practical examples and exercises were provided to reinforce these concepts. In the next module, we will delve into more advanced topics in C++ programming.

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