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C++ << operator use within class

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Started by breakspirit October 13, 2011 03:38 AM

4 comments, last by bubu LV 12 years, 6 months ago

breakspirit

100

Author

October 13, 2011 03:38 AM

Hey guys, please help me accomplish the following: I have a class called GameSimulation and I have the << operator set up so i can do

GameSimulation gameObject;

gameObject << "some text";

and the game will output that text in a specific way. Well, that works fine if i do that in main. However, how do i do the same thing from within the class?
For example, here's a function in the class definition:

 void GameSimulation::setUpNewPlayer(Player *player) 

{ 	gameWorld[player->location[0]] [player->location[1]] = player->sprite;   

       ???? << "New player has been set up.  There are now " << playerList.size() << " players online\n";

 }

What do I put in place of the question marks to make it use the GameSimulation::operator << (std::string textString) method that's in the same class? Thanks for your help.

Edit: I tried 'this' and '*this' and neither worked.

NumberXaero

2,625

October 13, 2011 04:15 AM

Try making the insertion operator a friend function.

<br>class GameSimulation

{

	public:   



    	friend GameSimulation&amp; operator &lt;&lt; (GameSimulation&amp; lhs, const char* s);



    	void Test()

    	{    	

        	*this &lt;&lt; "Test Text";

    	}

};



inline GameSimulation&amp; operator &lt;&lt; (GameSimulation&amp; lhs, const char* s)

{

   // do something



return lhs;

}<br>

Edit: the forum is not formatting or something.

breakspirit

100

Author

October 13, 2011 04:28 AM

Try making the insertion operator a friend function.   class GameSimulation { public: friend GameSimulation& operator << (GameSimulation& lhs, const char* s); void Test() { *this << "Test Text"; } }; inline GameSimulation& operator << (GameSimulation& lhs, const char* s) { // do something return lhs; }  Edit: the forum is not formatting or something.

That has indeed worked, thank you. I've got a couple questions though:
Why make the char* a const?
Is there any reason I shouldn't do a string instead of a character? Using character, it only outputs the first character. Using string, it outputs the whole string. I just want to make sure there isn't some good reason not to do the following:

inline GameSimulation& operator << (GameSimulation& lhs, std::string inputString)

{

//some stuff here



	std::cout << inputString;



	return lhs;

}

NumberXaero

2,625

October 13, 2011 04:37 AM

Use string, I just wrote const char* for that example, writing it as a friend function was the main point.

breakspirit

100

Author

October 13, 2011 04:43 AM

Gotcha, thanks for the help.

I'll avoid creating a new thread and just ask a followup question here:

Suppose I want the << operator to work with multiple data types and not just strings. Would I have to overload the function repeatedly for every operator I'd want like this;

inline GameSimulation& operator << (GameSimulation& lhs, const std::string inputString)

{

	//stuff

}



inline GameSimulation& operator << (GameSimulation& lhs, const int inputInt)

{

	//stuff

}

Or is there a way to make the input value something more generic? Thanks.

bubu LV

1,436

October 13, 2011 05:17 AM

It depends on what you want to do in "stuff". If you want to perform operation which is defined for all types you are passing, then it is possible:

template <class T>

inline GameSimulation& operator << (GameSimulation& lhs, const T& input)

{

    std::cout << input;

    return lhs;

}

In this example std::cout can process with << operator both types - int and std::string, so this will work as long as std::cout has appropriate << operator.

If your types need to be processed differently, then you must create separate functions, or at least extract this different functionality in separate function (like std::cout does for << ).

L. Spiro

25,818

October 13, 2011 05:31 AM

Hey guys, please help me accomplish the following: I have a class called GameSimulation and I have the << operator set up so i can do
GameSimulation gameObject; gameObject << "some text";

and the game will output that text in a specific way. Well, that works fine if i do that in main. However, how do i do the same thing from within the class?
For example, here's a function in the class definition:
void GameSimulation::setUpNewPlayer(Player *player) { gameWorld[player->location[0]] [player->location[1]] = player->sprite; ???? << "New player has been set up. There are now " << playerList.size() << " players online\n"; }
What do I put in place of the question marks to make it use the GameSimulation::operator << (std::string textString) method that's in the same class? Thanks for your help.

Edit: I tried 'this' and '*this' and neither worked.

(*this) << "New player has been set up. There are now " << playerList.size() << " players online\n";

L. Spiro

I restore Nintendo 64 video-game OST’s into HD! https://www.youtube.com/channel/UCCtX_wedtZ5BoyQBXEhnVZw/playlists?view=1&sort=lad&flow=grid

C++ << operator use within class

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