System Components

Developing a system component for an operating system in C++ involves a wide range of low-level tasks. The relevant Boost libraries will largely depend on the specifics of your project. Some operating systems may not support all of the features of these libraries, and for low-level tasks, it may be more appropriate to use system APIs directly. For higher-level system operations, or cross-platform tasks, Boost libraries have a lot to offer.

Libraries

Here are some Boost libraries that are useful in building system components:

  • Boost.Filesystem : This library provides a portable way of querying and manipulating paths, files, and directories. It can be very helpful for system-level tasks that need to interact with the file system.

  • Boost.ProgramOptions : This library allows program options to be defined, with types and default values, and their values to be retrieved from the command line, from config files, and programmatically.

  • Boost.System : This library provides simple, light-weight error_code objects that encapsulate system-specific "error codes", distinct from C++ exceptions.

  • Boost.Chrono : This library provides a set of handy features for measuring time, which might be useful for system-level tasks that need to measure or manipulate time.

  • Boost.Asio : This library provides a consistent asynchronous model using a modern C++ approach for network and low-level I/O programming. This might be useful for network-related components or any component that interacts with hardware.

  • Boost.Interprocess : This library provides a way of sharing memory and communicating between processes. It’s useful for creating shared memory regions, handling inter-process communication, managing shared objects, and synchronizing processes.

  • Boost.Thread : This library provides a portable interface for multithreading. It includes features for creating and managing threads, mutexes, condition variables, and futures.

  • Boost.Fiber : A fiber is a lightweight thread of execution. Boost.Fiber provides a framework for creating and managing fibers, which can be useful in some system-level programming tasks.

  • Boost.Container : This provides advanced data structures beyond the ones provided by the C++ standard library, which may be useful in certain scenarios.

  • Boost.Process : This library allows you to create child processes, setup their environment and provides means to communicate with them asynchronously through various streams.

Sample System File and Error Handling

Two core features of most systems are in file handling and robust error reporting. For a simpler sample we’ll create an app that uses Boost.Filesystem to manipulate files and directories, and Boost.System to capture and display specific errors.

The following sample creates a directory (example_directory) if it does not exist, writes a file (example_file.txt.) to the directory, reads from the file, and handles system-specific errors. Finally, it cleans up by deleting the file and directory, still handling any errors.

For examples of networking and threading code, refer to Networking and Parallel Computation.

#include <boost/filesystem.hpp>
#include <boost/system/error_code.hpp>
#include <iostream>
#include <fstream>

namespace fs = boost::filesystem;
namespace sys = boost::system;

//  Check and report system-specific errors
void handle_error(const sys::error_code& ec, const std::string& action) {
    if (ec) {
        std::cerr << "Error while " << action << ": " << ec.message()
                  << " (Code: " << ec.value() << ")\n";
    }
}

int main() {
    fs::path dir = "example_directory";
    fs::path file = dir / "example_file.txt";
    sys::error_code ec;

    // Create directory if it doesn't exist
    if (!fs::exists(dir)) {
        fs::create_directory(dir, ec);
        handle_error(ec, "creating directory");
    }

    // Write to the file
    {
        std::ofstream ofs(file.string());
        if (!ofs) {
            std::cerr << "Failed to open file for writing!\n";
            return 1;
        }
        ofs << "Hello, Boost.Filesystem!\n";
    }

    // Read from the file
    {
        std::ifstream ifs(file.string());
        if (!ifs) {
            std::cerr << "Failed to open file for reading!\n";
            return 1;
        }
        std::string content;
        std::getline(ifs, content);
        std::cout << "File content: " << content << '\n';
    }

    // Remove file
    fs::remove(file, ec);
    handle_error(ec, "removing file");

    // Remove directory
    fs::remove(dir, ec);
    handle_error(ec, "removing directory");

    return 0;
}
Note

Boost.Filesystem ensures directory and file management is platform-independent.

Support Configuration Settings

We are now going to include Boost.ProgramOptions to allow configuration settings via command-line arguments and configuration files.

The code now allows users to specify directory and file names, reads settings from a .ini file, and uses default values when one is not specified.

#include <boost/filesystem.hpp>
#include <boost/system/error_code.hpp>
#include <boost/program_options.hpp>
#include <iostream>
#include <fstream>

namespace fs = boost::filesystem;
namespace sys = boost::system;
namespace po = boost::program_options;

//  Check and report system-specific errors
void handle_error(const sys::error_code& ec, const std::string& action) {
    if (ec) {
        std::cerr << "Error while " << action << ": " << ec.message()
                  << " (Code: " << ec.value() << ")\n";
    }
}

int main(int argc, char* argv[]) {
    // Default configuration values
    std::string dir = "default_directory";
    std::string filename = "default_file.txt";
    std::string config_file = "config.ini";

    // Define command-line options
    po::options_description desc("Allowed options");
    desc.add_options()
        ("help,h", "Show help message")
        ("dir,d", po::value<std::string>(&dir), "Directory name")
        ("file,f", po::value<std::string>(&filename), "File name")
        ("config,c", po::value<std::string>(&config_file)->default_value("config.ini"), "Configuration file");

    // Parse command-line options
    po::variables_map vm;
    po::store(po::parse_command_line(argc, argv, desc), vm);
    po::notify(vm);

    if (vm.count("help")) {
        std::cout << desc << std::endl;
        return 0;
    }

    // Read options from configuration file (if available)
    std::ifstream ifs(config_file);
    if (ifs) {
        po::store(po::parse_config_file(ifs, desc), vm);
        po::notify(vm);
    }

    fs::path directory(dir);
    fs::path file = directory / filename;
    sys::error_code ec;

    // Create directory if it doesn't exist
    if (!fs::exists(directory)) {
        fs::create_directory(directory, ec);
        handle_error(ec, "creating directory");
    }

    // Write to the file
    {
        std::ofstream ofs(file.string());
        if (!ofs) {
            std::cerr << "Failed to open file for writing!\n";
            return 1;
        }
        ofs << "Hello, Boost.Program_Options and Boost.Filesystem!\n";
    }

    // Read from the file
    {
        std::ifstream ifs(file.string());
        if (!ifs) {
            std::cerr << "Failed to open file for reading!\n";
            return 1;
        }
        std::string content;
        std::getline(ifs, content);
        std::cout << "File content: " << content << '\n';
    }

    // Remove file
    fs::remove(file, ec);
    handle_error(ec, "removing file");

    // Remove directory
    fs::remove(directory, ec);
    handle_error(ec, "removing directory");

    return 0;
}

The command line options accepted by the sample are:

Option Description

--dir or -d

Specify the directory.

--file or -f

Specify the filename.

--config or -c

Specify the configuration file.

--help or -h

Display available options.

The following is an example config.ini file:

dir = my_directory
file = my_file.txt

The following command lines show how to run with defaults, run with options specified manually, and then run with a config file:

./program

./program --dir=my_data --file=data.txt

./program --config=my_config.ini

Time the System Operations

It might be important to record the time taken for system operations, both in testing and in the operation of a system app. So, let’s integrate Boost.Chrono to measure the time taken for key filesystem operations, such as creating directories, writing to files, reading files, and deleting files.

#include <boost/filesystem.hpp>
#include <boost/system/error_code.hpp>
#include <boost/program_options.hpp>
#include <boost/chrono.hpp>
#include <iostream>
#include <fstream>

namespace fs = boost::filesystem;
namespace sys = boost::system;
namespace po = boost::program_options;
namespace chrono = boost::chrono;

//  Check and report system-specific errors
void handle_error(const sys::error_code& ec, const std::string& action) {
    if (ec) {
        std::cerr << "Error while " << action << ": " << ec.message()
                  << " (Code: " << ec.value() << ")\n";
    }
}

int main(int argc, char* argv[]) {
    // Default configuration values
    std::string dir = "default_directory";
    std::string filename = "default_file.txt";
    std::string config_file = "config.ini";

    // Define command-line options
    po::options_description desc("Allowed options");
    desc.add_options()
        ("help,h", "Show help message")
        ("dir,d", po::value<std::string>(&dir), "Directory name")
        ("file,f", po::value<std::string>(&filename), "File name")
        ("config,c", po::value<std::string>(&config_file)->default_value("config.ini"), "Configuration file");

    // Parse command-line options
    po::variables_map vm;
    po::store(po::parse_command_line(argc, argv, desc), vm);
    po::notify(vm);

    if (vm.count("help")) {
        std::cout << desc << std::endl;
        return 0;
    }

    // Read options from configuration file (if available)
    std::ifstream ifs_config(config_file);
    if (ifs_config) {
        po::store(po::parse_config_file(ifs_config, desc), vm);
        po::notify(vm);
    }

    fs::path directory(dir);
    fs::path file = directory / filename;
    sys::error_code ec;

    // Measure time for directory creation
    auto start = chrono::steady_clock::now();
    if (!fs::exists(directory)) {
        fs::create_directory(directory, ec);
        handle_error(ec, "creating directory");
    }
    auto end = chrono::steady_clock::now();
    std::cout << "Directory creation took: "
              << chrono::duration_cast<chrono::microseconds>(end - start).count()
              << " microseconds\n";

    // Measure time for writing to file
    start = chrono::steady_clock::now();
    {
        std::ofstream ofs(file.string());
        if (!ofs) {
            std::cerr << "Failed to open file for writing!\n";
            return 1;
        }
        ofs << "Hello, Boost.Program_Options, Boost.Filesystem, and Boost.Chrono!\n";
    }
    end = chrono::steady_clock::now();
    std::cout << "File writing took: "
              << chrono::duration_cast<chrono::microseconds>(end - start).count()
              << " microseconds\n";

    // Measure time for reading from file
    start = chrono::steady_clock::now();
    {
        std::ifstream ifs(file.string());
        if (!ifs) {
            std::cerr << "Failed to open file for reading!\n";
            return 1;
        }
        std::string content;
        std::getline(ifs, content);
        std::cout << "File content: " << content << '\n';
    }
    end = chrono::steady_clock::now();
    std::cout << "File reading took: "
              << chrono::duration_cast<chrono::microseconds>(end - start).count()
              << " microseconds\n";

    // Measure time for file deletion
    start = chrono::steady_clock::now();
    fs::remove(file, ec);
    handle_error(ec, "removing file");
    end = chrono::steady_clock::now();
    std::cout << "File deletion took: "
              << chrono::duration_cast<chrono::microseconds>(end - start).count()
              << " microseconds\n";

    // Measure time for directory deletion
    start = chrono::steady_clock::now();
    fs::remove(directory, ec);
    handle_error(ec, "removing directory");
    end = chrono::steady_clock::now();
    std::cout << "Directory deletion took: "
              << chrono::duration_cast<chrono::microseconds>(end - start).count()
              << " microseconds\n";

    return 0;
}
Note

This code measures execution time in microseconds for each operation.

The following is example output from running our sample.

$ ./program --dir=my_data --file=myfile.txt
Directory creation took: 187 microseconds
File writing took: 112 microseconds
File content: Hello, Boost.Program_Options, Boost.Filesystem, and Boost.Chrono!
File reading took: 98 microseconds
File deletion took: 75 microseconds
Directory deletion took: 88 microseconds

Adding timing features to your system operations will help you maintain more robust and performance-aware code, so as code is updated you will have built in the checks and balances so that if something goes awry - you will be able to capture and correct it early in the development cycle.

See Also

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