Back to General and Gameplay Programming

Isn't it possible to use the - operator in a constructor argument?

General and Gameplay Programming Programming

Started by JWColeman December 01, 2009 11:58 PM

11 comments, last by InvalidPointer 14 years, 4 months ago

JWColeman

147

Author

December 01, 2009 11:58 PM


Plane left(-100,0);

Because that bit of code right there gives me this error:

c:\users\jonathan\documents\nehegl\logic.h(14) : error C2059: syntax error : '-'

Here is the structure I'm trying to create:


struct Plane
{
	Plane(int x, int y)
	{
		position.x = x;
		position.y = y;
		normal = position.normal();
	}
	Vector2 position;
	Vector2 normal;
};

I could be wrong, but last time I checked you could use operators in arguments?

My Frogger Challenge Project - Gogger

Endurion

5,545

December 02, 2009 12:02 AM

Of course that's possible. Show the constructor call.

Fruny: Ftagn! Ia! Ia! std::time_put_byname! Mglui naflftagn std::codecvt eY'ha-nthlei!,char,mbstate_t>

JWColeman

147

Author

December 02, 2009 12:04 AM

I'm just trying to initialize these planes so I can test my plane intersection function:

class Logic{public:	Logic();	Plane left(-100,0);	void move_paddle(Vector2 direction, Paddle & gamePaddle);	void check_collision();private:		bool collision2d(Vector2 & a_min, Vector2 & a_max, Vector2 & b_min, Vector2 & b_max);	bool planeCollision2d(Plane & boundingPlane, Vector2 & objectPosition);	void check_paddle_collision();	void reverse_y_velocity(Vector2 & velocity);	void reverse_x_velocity(Vector2 & velocity);	Ball * ball;	Player * player1;	Player * player2;};

My Frogger Challenge Project - Gogger

Black Knight

769

December 02, 2009 12:06 AM

Are you doing anything that is listed here :

linky

Seeing more code would help too :)

You can't init a member inside the class declaration you need to do it at the class' constructor initializer list.

class Logic{public:	Logic():left(-100,0) {}	Plane left;	void move_paddle(Vector2 direction, Paddle & gamePaddle);	void check_collision();private:		bool collision2d(Vector2 & a_min, Vector2 & a_max, Vector2 & b_min, Vector2 & b_max);	bool planeCollision2d(Plane & boundingPlane, Vector2 & objectPosition);	void check_paddle_collision();	void reverse_y_velocity(Vector2 & velocity);	void reverse_x_velocity(Vector2 & velocity);	Ball * ball;	Player * player1;	Player * player2;};

[ShadowyTree][MyPortfolio]

JWColeman

147

Author

December 02, 2009 12:08 AM

#ifndef PLANE_H#define PLANE_H#include "Vector2.h"struct Plane{	Plane(int x, int y)	{		position.x = x;		position.y = y;		normal = position.normal();	}	Vector2 position;	Vector2 normal;};#endif

And

#ifndef LOGIC_H#define LOGIC_H#include "Paddle.h"#include "Ball.h"#include "Vector2.h"#include "Ray.h"#include "Plane.h"#include "Player.h"class Logic{public:	Logic();	Plane left(-100,0);	void move_paddle(Vector2 direction, Paddle & gamePaddle);	void check_collision();private:		bool collision2d(Vector2 & a_min, Vector2 & a_max, Vector2 & b_min, Vector2 & b_max);	bool planeCollision2d(Plane & boundingPlane, Vector2 & objectPosition);	void check_paddle_collision();	void reverse_y_velocity(Vector2 & velocity);	void reverse_x_velocity(Vector2 & velocity);	Ball * ball;	Player * player1;	Player * player2;};#endif

My Frogger Challenge Project - Gogger

JWColeman

147

Author

December 02, 2009 12:09 AM

Oooooohhhhhs, understood!

My Frogger Challenge Project - Gogger

JWColeman

147

Author

December 02, 2009 12:12 AM

Quote:Original post by Black Knight
Are you doing anything that is listed here :

linky

Seeing more code would help too :)

You can't init a member inside the class declaration you need to do it at the class' constructor initializer list.

*** Source Snippet Removed ***

Also, if I want to do more than one, do I use another : to separate them? Or something else? Because it gives me an error if I do this:

	Logic():left(-100,0):right(100,0):top(0,100):bottom(0,-100)	{		player1 = new Player;		player2 = new Player;		ball = new Ball;	}

Sorry I'm a noob at this syntax, never used this feature before, surprisingly lol

My Frogger Challenge Project - Gogger

JWColeman

147

Author

December 02, 2009 12:14 AM

a ,! I figured it out, lol I post faster than I edit my code lol

My Frogger Challenge Project - Gogger

JWColeman

147

Author

December 02, 2009 12:15 AM

IT WORKS!!!

void Logic::check_collision(){ if(ball->getVelocity().x > 0)		{			if (collision2d(ball->getMinimum(), ball->getMaximum(), player2->paddle->getMinimum(), player2->paddle->getMaximum()))			{				reverse_x_velocity(ball->getVelocity());			}			else if(planeCollision2d(right, ball->getLocation()))			{				reverse_x_velocity(ball->getVelocity());				ball->getLocation().x = 0;				ball->getLocation().y = 0;				player1->goal();			}		}		if(ball->getVelocity().x < 0)		{			if (collision2d(ball->getMinimum(), ball->getMaximum(), player1->paddle->getMinimum(), player1->paddle->getMaximum()))			{				reverse_x_velocity(ball->getVelocity());			}			else if(planeCollision2d(left, ball->getLocation()))			{				reverse_x_velocity(ball->getVelocity());				ball->getLocation().x = 0;				ball->getLocation().y = 0;				player2->goal();			}		}		if(ball->getVelocity().y > 0)		{			if (planeCollision2d(top, ball->getLocation()))			{				reverse_y_velocity(ball->getVelocity());			}		}		if(ball->getVelocity().y < 0)		{			if (planeCollision2d(bottom, ball->getLocation()))			{				reverse_y_velocity(ball->getVelocity());			}		}	}

My Frogger Challenge Project - Gogger

Black Knight

769

December 02, 2009 12:39 AM

Also you are allocating dynamically but I don't see your destructor so that memory is not freed.

You should have a destructor that deletes these guys
player1 = new Player;
player2 = new Player;
ball = new Ball;

Logic::~Logic()
{
delete player1;
delete player2;
delete ball;
}

Though player and ball being a member of logic doesn't make much sense :)

You should also watch out for memory leaks that might occur in your constructor.The thing is in C++ when a class throws an exception from the constructor its destructor is never called.So imagine what happens when
player1 = new Player;
player2 = new Player;

allocate memory and then new Ball;(constructor of Ball) throws an exception.This means ~Logic will not be called and you won't be able to delete player1 and player2.

Here is an example that shows this :

#include <iostream>#include <string>#include <exception>#include <memory>using std::cout;using std::endl;class Player{public : 	Player()	{		cout<<"Player constructor called"<<endl;	}	~Player()	{		cout<<"Player destructor called"<<endl;	}	};class Ball{public : 	Ball()	{		throw std::runtime_error("Ball threw exception");		cout<<"Ball constructor called"<<endl;	}	~Ball()	{		cout<<"Ball destructor called"<<endl;	}};class Logic{public:	Logic():	  player1(new Player()),	  player2(new Player()),	  ball(new Ball())	{		}	~Logic()	{			}	Player* player1;	Player* player2;	Ball* ball;};int main(){		try	{		Logic gameLogic;	}	catch(const std::runtime_error& e)	{		cout<<e.what()<<endl;	}				return 0;}

And here is how it is fixed by using a shared_ptr

#include <iostream>#include <string>#include <exception>#include <memory>using std::cout;using std::endl;class Player;class Ball;typedef std::tr1::shared_ptr<Player> PlayerPtr;typedef std::tr1::shared_ptr<Ball> BallPtr;class Player{public : 	Player()	{		cout<<"Player constructor called"<<endl;	}	~Player()	{		cout<<"Player destructor called"<<endl;	}	};class Ball{public : 	Ball()	{		throw std::runtime_error("Ball threw exception");		cout<<"Ball constructor called"<<endl;	}	~Ball()	{		cout<<"Ball destructor called"<<endl;	}};class Logic{public:	Logic():	  player1(new Player()),	  player2(new Player()),	  ball(new Ball())	{		}	~Logic()	{			}	PlayerPtr player1;	PlayerPtr player2;	BallPtr ball;};int main(){		try	{		Logic gameLogic;	}	catch(const std::runtime_error& e)	{		cout<<e.what()<<endl;	}				return 0;}

To understand how this works you need to read on stack unwinding and what happens when an exception is thrown.

[ShadowyTree][MyPortfolio]

Isn't it possible to use the - operator in a constructor argument?

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Isn't it possible to use the - operator in a constructor argument?

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines