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static class vs this?

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Started by nuclear123 March 30, 2011 06:26 PM

21 comments, last by Hodgman 13 years ago

nuclear123

119

Author

March 30, 2011 06:26 PM

is there a difference/overhead in doing this....



class Log

{

private: // no members

public:

       void createLog( );

};



int main()

{



Log log1;

log1.createLog();



}







class Log

{

private: // no members

public:

       static void createLog( );

};





int main()

{

Log::createLog();

}

is this the same exact code? or does the non static one create useless overhead and is bad code/slower

frob

46,221

March 30, 2011 07:12 PM

No, they are not the same.

A static member function does not operate on an object.
A non-static member function must have an object, which is automatically passed to the function as the this pointer.

The performance difference between the two is very nearly nothing.

Generally you use a static member function when you want a function to be part of a class interface but you won't actually reference a part of the object. For example, you may use it to look up common values.

I'm guessing that eventually createLog is going to modify the state of a Log object, so it shouldn't be a static function.

way2lazy2care

793

March 30, 2011 07:22 PM

This looks eerily like you are going to implement singletons...

NicoG

172

March 30, 2011 07:26 PM

If you want Log to be available with the same instance everywhere, think about using a Singleton.



class Log : public boost::noncopyable

{

private:

 	Log()

	{}



public:

 	static Log& getInstance()

	{

 		static Log OnlyOne;

 		return OnlyOne;

	}



	void createLog() 

	{

 		// .....

	}



   void logIt(int, string&)

   {}

};



#define LOGERROR(s)	Log::getInstance().logIt(L_ERROR, s)



int main()

{

	Log::getInstance().createLog();

	LOGERROR("I am feeling depressed.");

}

Static Values can also be used to define Strings or things used over the whole program:



class Math

{

	static double PI;

};



double Math::PI = 3.14159265;



int main()

{

	using namespace std;

	cout << "PI is exactly: " << Math::PI << endl;

}

If you say "pls", because it is shorter than "please", I will say "no", because it is shorter than "yes"
http://nightlight2d.de/

Zakwayda

2,389

March 31, 2011 05:17 AM

If you want Log to be available with the same instance everywhere, think about using a Singleton.

Why not just use a global?

Hodgman

52,717

March 31, 2011 05:35 AM

I'd expect a modern compiler to create the same code for both cases.

The only difference is that one is an evil global, and one isn't.

. 22 Racing Series .

rip-off

11,000

March 31, 2011 09:42 AM

If logging is your bottleneck then you are doing it wrong. In any case with logging the slow part is usually the I/O, not the function calls themselves. Don't micro optimise unless you have a performance problem and you have exhausted macro optimisations.

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NicoG

172

March 31, 2011 09:59 AM

[quote name='NicoG' timestamp='1301513209' post='4792295']
If you want Log to be available with the same instance everywhere, think about using a Singleton.

Why not just use a global?
[/quote]

Of course could he use a global, but in my eyes a singleton provides a cleaner access-interface.

If you say "pls", because it is shorter than "please", I will say "no", because it is shorter than "yes"
http://nightlight2d.de/

rip-off

11,000

March 31, 2011 10:58 AM

I believe a Singleton provides a worse interface. It tends to be more verbose, and it is harder to create sub-system local log instances. For example, you might want to set the log verbosity of your graphics subsystem to high, while keeping others low. For low complexity games, I'd probably just use simple procedure calls rather than create a class at all. Any state can be kept in an anonymous namespace.

Or just use std::cout, std::cerr and std::clog directly. I might modify their rdbuf() to output to a in-game console or to a file, or I might use OS-level pipes to capture the output to a file.

blog | twitter

NicoG

172

March 31, 2011 11:09 AM

I believe a Singleton provides a worse interface. It tends to be more verbose, and it is harder to create sub-system local log instances. For example, you might want to set the log verbosity of your graphics subsystem to high, while keeping others low. For low complexity games, I'd probably just use simple procedure calls rather than create a class at all. Any state can be kept in an anonymous namespace.

Or just use std::cout, std::cerr and std::clog directly. I might modify their rdbuf() to output to a in-game console or to a file, or I might use OS-level pipes to capture the output to a file.

When you use a singleton, it is guaranteed that you cannot access the singleton before it is created. Hence getInstance().
You don't have that guarantee with static globals.

I use such a logging singleton for creating html logs. You can represent debugging data much better with that when you are unable to pause the process because it depends on timing etc, which is esp. the case when you are doing games. Well, at least it is an easy method to achieve this.
I made myself a class log and logwriter. logwriter can be derived and output any format such as csv, text or html.

If you say "pls", because it is shorter than "please", I will say "no", because it is shorter than "yes"
http://nightlight2d.de/

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