20 How to Write a C++ Class

1. Log Class

Logging is crucial during development and debugging, and it serves as a great example.

#include <iostream>

class Log
{
public:  // public methods, variables, and static variables can be separated
    const int LogLevelError = 0;
    const int LogLevelWarning = 1;
    const int LogLevelInfo = 2;
private:
    int m_LogLevel = LogLevelInfo;  // stands for member
public:
    void SetLevel(int level)
    {
        m_LogLevel = level; // helps distinguish between member variables and local variables
    }

    void Error(const char* message)
    {
        if (m_LogLevel >= LogLevelError)
            std::cout << "[ERROR]:" << message << std::endl;
    }

    void Warn(const char* message)
    {
        if (m_LogLevel >= LogLevelWarning)
            std::cout << "[WARNING]:" << message << std::endl;
    }

    void Info(const char* message)
    {
        if (m_LogLevel >= LogLevelInfo)
        std::cout << "[INFO]:" << message << std::endl;
    }
};

int main()
{
    Log log;
    log.SetLevel(log.LogLevelWarning);  // m_LogLevel = 1
    log.Warn("Hello!");
    log.Error("Hello!");
    log.Info("Hello");    // Warn + Error 
    std::cin.get();
}

This code is quite rough, but it follows a general approach. That is, first write the methods and variables that might be used in main, and then expand the class. Later, we will learn how to improve it.

class Log
{
public:
    enum Level
    {
        LevelError = 0, LevelWarning, LevelInfo
    };
private:
    Level m_LogLevel = LevelInfo;  
public:
    void SetLevel(Level level)
    {
        m_LogLevel = level; 
    }

    void Error(const char* message)
    {
        if (m_LogLevel >= LevelError)
            std::cout << "[ERROR]:" << message << std::endl;
    }

    void Warn(const char* message)
    {
        if (m_LogLevel >= LevelWarning)
            std::cout << "[WARNING]:" << message << std::endl;
    }

    void Info(const char* message)
    {
        if (m_LogLevel >= LevelInfo)
            std::cout << "[INFO]:" << message << std::endl;
    }
};

int main()
{
    Log log;
    log.SetLevel(log.LevelError);  // m_LogLevel = 0, Log::LevelError
    log.Warn("Hello!");
    log.Error("Hello!");
    log.Info("Hello");    // Warn + Error 
    std::cin.get();
}