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RTTI in Logging and Debugging

How can I use RTTI to implement a robust logging system that provides detailed type information for debugging?

Implementing a robust logging system using RTTI can greatly enhance debugging by providing detailed type information. Here's an approach to create such a system:

Define a base Loggable class:

#include <typeinfo>
#include <string>

class Loggable {
 public:
  virtual ~Loggable() = default;
  virtual std::string getLogInfo() const {
    return std::string("Type: ") +
      typeid(*this).name();
  }
};

Implement a Logger class:

#include <typeinfo>
#include <string>
#include <chrono>
#include <iostream>


class Loggable {/*...*/}

class Logger {
 public:
  enum class LogLevel {
    DEBUG, INFO, WARNING, ERROR
  };

  static void log(
    LogLevel level,
    const Loggable& obj,
    const std::string& message
  ) {
    std::ostringstream oss;
    oss << getCurrentTimestamp() << " ["
      << getLevelString(level) << "] "
      << obj.getLogInfo() << " - " << message;
    std::cout << oss.str() << std::endl;
  }

  static std::string getCurrentTimestamp() {
    using namespace std::chrono;
    auto now = system_clock::now();
    auto time = system_clock::to_time_t(now);
    std::stringstream ss;
    ss << std::put_time(
      std::localtime(&time), "%Y-%m-%d %H:%M:%S"
    );
    return ss.str();
  }

  static std::string getLevelString(
    LogLevel level) {
    switch (level) {
      case LogLevel::DEBUG:
        return "DEBUG";
      case LogLevel::INFO:
        return "INFO";
      case LogLevel::WARNING:
        return "WARNING";
      case LogLevel::ERROR:
        return "ERROR";
      default:
        return "UNKNOWN";
    }
  }
};

Create loggable classes:

#include <typeinfo>
#include <string>
#include <chrono>
#include <iostream>


class Loggable {/*...*/}


class Logger {/*...*/}

class Player : public Loggable {
 public:
  Player(const std::string& name, int health)
    : name_(name), health_(health) {}

  std::string getLogInfo() const override {
    std::ostringstream oss;
    oss << Loggable::getLogInfo() << ", Name: "
      << name_ << ", Health: " << health_;
    return oss.str();
  }

  void takeDamage(int Damage) {
    // ...
  }

 private:
  std::string name_;
  int health_;
};

class Item : public Loggable {
 public:
  Item(const std::string& name, int value)
    : name_(name), value_(value) {}

  std::string getLogInfo() const override {
    std::ostringstream oss;
    oss << Loggable::getLogInfo() << ", Name: "
      << name_ << ", Value: " << value_;
    return oss.str();
  }

 private:
  std::string name_;
  int value_;
};

Implement a template function for logging types that do not inherit from Loggable:

#include <typeinfo>
#include <string>
#include <chrono>
#include <iostream>


class Loggable {/*...*/}


class Logger {/*...*/}


class Player : public Loggable {/*...*/}


class Item : public Loggable {/*...*/}

template <typename T>
void logValue(
  Logger::LogLevel level,
  const T& value,
  const std::string& message
) {
  std::ostringstream oss;
  oss << "Type: " << typeid(value).name()
    << ", Value: " << value;
  std::cout << Logger::getCurrentTimestamp()
    << " [" << Logger::getLevelString(level)
    << "] " << oss.str() << " - "
    << message << std::endl;
}

Use the logging system:

#include <typeinfo>
#include <string>
#include <chrono>
#include <iostream>


class Loggable {/*...*/}


class Logger {/*...*/}


class Player : public Loggable {/*...*/}


class Item : public Loggable {/*...*/}


void logValue(/*...*/) {/*...*/}

int main() {
  Player player("Alice", 100);
  Logger::log(Logger::LogLevel::INFO,
    player, "Player created");

  Item sword("Excalibur", 1000);
  Logger::log(Logger::LogLevel::DEBUG,
    sword, "Item acquired");

  player.takeDamage(20);
  Logger::log(Logger::LogLevel::WARNING,
    player, "Player took damage");

  int score = 5000;
  logValue(Logger::LogLevel::INFO, score,
    "Current score");

  std::string gameState = "Level 2";
  logValue(Logger::LogLevel::DEBUG, gameState,
    "Game state changed");

  try {
    throw std::runtime_error("Game crash");
  } catch (const std::exception& e) {
    Logger::log(Logger::LogLevel::ERROR,
      player, std::string("Exception: ") + e.what());
  }
}
2024-06-24 03:54:24 [INFO] Type: class Player, Name: Alice, Health: 100 - Player created
2024-06-24 03:54:24 [DEBUG] Type: class Item, Name: Excalibur, Value: 1000 - Item acquired
2024-06-24 03:54:24 [WARNING] Type: class Player, Name: Alice, Health: 100 - Player took damage
2024-06-24 03:54:24 [INFO] Type: int, Value: 5000 - Current score
2024-06-24 03:54:24 [DEBUG] Type: class std::string, Value: Level 2 - Game state changed
2024-06-24 03:54:24 [ERROR] Type: class Player, Name: Alice, Health: 100 - Exception: Game crash

This logging system uses RTTI in several ways:

  1. The base Loggable class uses typeid to provide the type name of derived classes.
  2. The logValue template function uses typeid to get type information for non-Loggable types.
  3. The Logger class provides a consistent interface for logging both Loggable and non-Loggable types.

Benefits of this approach:

  • Detailed type information: The system provides the actual type of objects being logged, which is especially useful for polymorphic types.
  • Extensibility: New Loggable classes can easily be added by inheriting from the Loggable base class and overriding the getLogInfo method.
  • Flexibility: The system can log both Loggable objects and primitive types.
  • Consistency: All log entries include timestamps, log levels, and type information.

Considerations:

  • Performance: RTTI operations have a runtime cost. In performance-critical sections, you might want to disable detailed logging or use compile-time alternatives.
  • Readability: The typeid().name() output is implementation-defined and might not be human-readable. You might need to use a demangling function for better readability.
  • Memory usage: Storing detailed type information for all objects might increase memory usage. Consider implementing a way to control logging verbosity.

To further enhance this system, you could:

  • Add file output capabilities to the Logger class.
  • Implement log filtering based on log levels or object types.
  • Use a thread-safe logging mechanism for multi-threaded applications.
  • Integrate with a more comprehensive logging framework like spdlog or Boost.Log.

By using RTTI in your logging system, you can create a powerful debugging tool that provides detailed type information at runtime, greatly aiding in the development and maintenance of complex C++ applications.

Run Time Type Information (RTTI) and typeid()

Learn to identify and react to object types at runtime using RTTI, dynamic casting and the typeid() operator

View Full Lesson

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