**Course Title:** Modern C++ Programming: Mastering C++ with Best Practices and Advanced Techniques **Section Title:** File I/O and Serialization **Topic:** Write a C++ program that reads from and writes to files, using both text and binary formats. (Lab topic) =========================================================================================== **Overview** --------------- In this lab topic, you will learn how to write a C++ program that reads from and writes to files using both text and binary formats. You will understand the differences between text and binary files, and how to use the `std::fstream` and `std::iomanip` classes to perform file input/output operations. **Text Files vs. Binary Files** ------------------------------ Text files are human-readable files that contain ASCII characters, while binary files are machine-readable files that contain binary data. Text files are useful for storing text data, such as configuration files or logs, while binary files are useful for storing image, audio, or video data. **Using `std::fstream` for File I/O** -------------------------------------- The `std::fstream` class provides a way to read from and write to files in C++. To use `std::fstream`, you need to include the `<fstream>` header file. Here is an example of how to use `std::fstream` to write to a text file: ```cpp #include <fstream> #include <string> int main() { std::ofstream outputFile("example.txt"); if (outputFile.is_open()) { std::string line = "Hello, World!"; outputFile << line << std::endl; outputFile.close(); } else { std::cerr << "Unable to open file"; } return 0; } ``` In this example, we create an `std::ofstream` object called `outputFile` and open the file "example.txt" in write mode. We then write a string to the file using the `<<` operator and close the file using the `close()` method. To read from a text file, you can use the `std::ifstream` class: ```cpp #include <fstream> #include <string> int main() { std::ifstream inputFile("example.txt"); if (inputFile.is_open()) { std::string line; while (inputFile >> line) { std::cout << line << std::endl; } inputFile.close(); } else { std::cerr << "Unable to open file"; } return 0; } ``` In this example, we create an `std::ifstream` object called `inputFile` and open the file "example.txt" in read mode. We then read from the file using the `>>` operator and print the contents to the console. **Using `std::iomanip` for Formatted I/O** ----------------------------------------- The `std::iomanip` class provides a way to perform formatted input/output operations in C++. To use `std::iomanip`, you need to include the `<iomanip>` header file. Here is an example of how to use `std::iomanip` to write to a text file: ```cpp #include <fstream> #include <iomanip> #include <string> int main() { std::ofstream outputFile("example.txt"); if (outputFile.is_open()) { std::string line = "Hello, World!"; outputFile << std::setw(20) << std::left << line << std::endl; outputFile.close(); } else { std::cerr << "Unable to open file"; } return 0; } ``` In this example, we create an `std::ofstream` object called `outputFile` and open the file "example.txt" in write mode. We then write a string to the file using the `<<` operator and format the output using the `std::setw` and `std::left` manipulators. **Writing to Binary Files** --------------------------- To write to a binary file, you can use the `std::ofstream` class with the `std::ios::binary` flag. Here is an example: ```cpp #include <fstream> #include <cstdint> int main() { std::ofstream outputFile("example.bin", std::ios::binary); if (outputFile.is_open()) { uint32_t value = 0x12345678; outputFile.write(reinterpret_cast<char*>(&value), sizeof(value)); outputFile.close(); } else { std::cerr << "Unable to open file"; } return 0; } ``` In this example, we create an `std::ofstream` object called `outputFile` and open the file "example.bin" in binary write mode. We then write a `uint32_t` value to the file using the `write()` method and a pointer cast. **Reading from Binary Files** --------------------------- To read from a binary file, you can use the `std::ifstream` class with the `std::ios::binary` flag. Here is an example: ```cpp #include <fstream> #include <cstdint> int main() { std::ifstream inputFile("example.bin", std::ios::binary); if (inputFile.is_open()) { uint32_t value; inputFile.read(reinterpret_cast<char*>(&value), sizeof(value)); std::cout << "Value: " << value << std::endl; inputFile.close(); } else { std::cerr << "Unable to open file"; } return 0; } ``` In this example, we create an `std::ifstream` object called `inputFile` and open the file "example.bin" in binary read mode. We then read a `uint32_t` value from the file using the `read()` method and a pointer cast. **Best Practices** ------------------- * Always check the status of the file stream after opening it to ensure that it is valid. * Use the `std::ios::binary` flag when reading or writing to binary files. * Use the `std::setw` and `std::left` manipulators to format output. * Always close the file stream after reading or writing to it to free up system resources. **Conclusion** ---------- In this lab topic, you learned how to write a C++ program that reads from and writes to files using both text and binary formats. You understood the differences between text and binary files, and how to use the `std::fstream` and `std::iomanip` classes to perform file input/output operations. We hope this topic has helped you understand file I/O and serialization in C++. If you have any questions or need further clarification, please don't hesitate to ask in the comments below. In the next topic, we will cover "Introduction to exception handling: `try`, `catch`, `throw`". References: * [std::fstream](https://en.cppreference.com/w/cpp/io/fstream) * [std::iomanip](https://en.cppreference.com/w/cpp/io/manip) * [std::ios::binary](https://en.cppreference.com/w/cpp/io/ios_base/openmode) Please leave a comment or ask for help if you need further clarification on any of the concepts covered in this topic.