Call a method of a static member for initialization in C++

Question

I have a class that has a static member object. Initializing that static object means setting some of its parameter to a specific value; but this is done by a function from that object. i do not know how to do it if it is static. Any help?

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To be more specific I have a static boost logger object per class. It has a ClasName attribute and setting this to the name_of_the_class value is done by add_attribute("ClassName", boost::log::attributes::constant<std::string>("MyClass")) function. What is the best way to initialize the static logger? I have done:

typedef boost::log::sources::severity_logger< severity_levels > BoostLogger;

class MyClass
{
private:
  static BoostLogger m_logger;

public:
  MyClass()
  {
    MyClass::m_logger.add_attribute("ClassName", boost::log::attributes::constant<std::string>("MyClass"));
  }
}

BoostLogger MyClass::m_logger; // And here I cannot call the add_attribute() function

I know that this is done every time I instantiate the class, so: What is the best way to do it?

Answer 1

You can initialise the logger once eg with a static variable in your constructor:

MyClass()
{
  static bool logger_initialised = false;
  if (!logger_initialised)
  {
    MyClass::m_logger.add_attribute("ClassName", boost::log::attributes::constant<std::string>("MyClass"));
    logger_initialised = true;
  }
}

Note that this is not thread-safe. But if you do not use threads, it will work and the logger will be initialised one time but only if you instantiate MyClass .

Answer 2

if BoostLogger doesn't provide the constructor to add_attribute you may create your own function for that, something like:

class MyClass
{
private:
    static BoostLogger m_logger;
};

BoostLogger CreateBoostLoggerWithClassName(const std::string& className)
{
    BoostLogger logger;
    logger.add_attribute(
        "ClassName",
        boost::log::attributes::constant<std::string>(className));
    return logger;
}

BoostLogger MyClass::m_logger = CreateBoostLoggerWithClassName("MyClass");

Answer 3

First of all look at the BOOST_LOG_GLOBAL_LOGGER

Here is corrected version of your code.

MyClass.h:

class MyClass
{
private:
  static BoostLogger m_logger;  /*  This is declaration, not definition.
                                    You need also define the member somewhere */

public:
  MyClass() /*  So far as this is constructor, it may be called more than once,
                I think adding new static function will be better */
  {
    // MyClass::m_logger.add_attribute("ClassName", boost::log::attributes::constant<std::string>("MyClass"));
    // AddAttribute("ClassName"); Uncomment this line if you're really need to add attribute in constructor
  }

  static void AddAttribute(std::string name) /* this function has been added as advice,
                                                if you're going add attributes as you
                                                did in question,
                                                remove function, and uncomment first              line in the constructor */
  {
    MyClass::m_logger.add_attribute(name, boost::log::attributes::constant<std::string>("MyClass"));
  }
}

MyClass.cpp:

BoostLogger MyClass::m_logger = BoostLogger(); // This is definition of static member item

Answer 4

Instead of an add_attribute call, make it so that you can fully initialise BoostLogger with its constructor. Then simply provide the necessary argument when you define it.