Okay I feel really stupid... I've been trying to create a Snake clone. Right now I'm just doing it in the console with a number grid - though it'll be easily be turned to graphics with SFML. Just trying to get the basics done before graphics.

Anyway...okay I was trying to do the snake with a linked list(Which I've never used before). Moves around just fine. Except I must be creating it incorrectly or something. Because I cannot seem to grab the end of the snake's coordinates. It continually thinks it's the same - and I want them in order to make it empty when the end moves.

I know I'm sure I'm doing plenty of unnecessary things. My brains just been fried and I think I know what it is, but just can't solve it. Ready for a brain replacement.

Code:

snake.h

#include <iostream>

#include "grid.h"

class Snake
{
public:
	Snake();

	enum Direction
	{
		UP,
		DOWN,
		LEFT,
		RIGHT,
	};

	void createSnake(Grid &grid);
	void move( Direction direct );
	void grow();

	int getPosX();
	int getPosY();

        ...

private:

	int mPosX;
	int mPosY;
	int mDirection;
	int mEndX;
	int mEndY;

	int getEndX();
	int getEndY();

	void moveNode( Snake *link, int x, int y );

	Snake *next;
	Snake *head;
	Snake *link;
        ...
};

snake.cpp

void Snake::createSnake(Grid &grid)
{
	mGrid = &grid;
	head = new Snake;
	head->next = 0;
	head->mPosX = 10;
	head->mPosY = 10;
	mGrid->setCell(grid.SNAKE, head->mPosX, head->mPosY);

	for( int i = 0; i < 2; i++ )
	{
		this->link = head;
		if( this->link != 0 )
		{
			this->link->next = new Snake;
			this->link = this->link->next;
			this->link->next = 0;
			this->link->mPosX = 11 + i;
			this->link->mPosY = 10;
			mGrid->setCell(mGrid->SNAKE, this->link->mPosX, this->link->mPosY);
		}
	}
	
}

int Snake::getEndX()
{
	this->link = head;
	while ( this->link->next != 0 ) 
	{
		this->link = this->link->next;
		std::cout << "X: " << this->link->mPosX << std::endl;
	}
	return this->link->mPosX;
}

int Snake::getEndY()
{
	this->link = head;
	while ( this->link->next != 0 ) 
	{
		this->link = this->link->next;
	}
	return this->link->mPosY;
}

void Snake::move( Direction direct )
{
	head->mDirection = direct;
	int origX = head->getPosX();
	int origY = head->getPosY();
	if( head->mDirection == LEFT )
	{
		head->mPosX -= 1;
	}
	else if( head->mDirection == RIGHT )
		head->mPosX += 1;
	else if( head->mDirection == UP )
		head->mPosY -= 1;
	else if( head->mDirection == DOWN )
		head->mPosY += 1;

	mGrid->setCell(mGrid->SNAKE, head->mPosX, head->mPosY);

	this->link = head;
	this->link = this->link->next;

	moveNode( this->link, origX, origY );
}

void Snake::moveNode( Snake *link, int x, int y )
{
	int tempX, tempY = 0;
	mEndX = getEndX();
	mEndY = getEndY();
	std::cout << std::endl << std::endl << "EndX: " << mEndX << " EndY: " << mEndY << std::endl << std::endl;

	//if( this->link->next != 0 )
	//{
		tempX = this->link->mPosX;
		tempY = this->link->mPosY;
		this->link->mPosX = x;
		this->link->mPosY = y;
		mGrid->setCell(mGrid->SNAKE, this->link->mPosX, link->mPosY);
		mGrid->setCell(mGrid->EMPTY, mEndX, mEndY);
		if( this->link->next != 0 )
		{
			this->link = this->link->next;
			moveNode( this->link, tempX, tempY );
		}
	//}
	this->link->mPosX = tempX;
	this->link->mPosY = tempY;
	mGrid->setCell(mGrid->SNAKE, this->link->mPosX, link->mPosY);
}

In Console:

http://imgur.com/DhN8kiv

http://imgur.com/8bLSoHw

I had never heard of the deque class, but it does sound interesting.
And yeah, my code does look a tad confusing huh? I didn't originally intend for the snake class to just be one node or look like that...accidentally evolved into it, err devolved.

As to a the Node's, what do you mean a payload? To hold what sort of information, the coordinates and things like that? How would it retrieve it - I'm sorry just a tad confused about it. I'll try to puzzle it out, like I said brain isn't working.
And I've never done a doubly linked list, just single. Hence further confusion.

And in your instance, the snake will grow from the inside out ( inserting in the middle ) ?

So the SnakeNode struct would simply be:

struct SnakeNode
{
    SnakeNode *prev;
    SnakeNode *next;
    //Payload? To a Snake class?
}
SnakeNode *root_node = new SnakeNode;
SnakeNode *tail_node = new SnakeNode;

Most of my confusion was how to correctly pass the head's( or root ) coordinates to the rest of the list, and the tail knowing where it was in order to delete behind it AND either save the node next to last or save the coordinates for where the head turns.

Also yes, Grid is the class that draws the board - it isn't an error in the drawing. ( Also fyi, the snake starts off with 3 nodes, first move to the left it's still 3, second move to the left it starts growing, etc )

Thanks for the reply.

Ohhh, well I'll see if I can puzzle the deque out. Oh okay, the payload isn't the SnakeNode, it's a SnakeSegment - that makes more sense now.

Hm, didn't think about that - that'd probably be easier if I figure it out. Definitely less fiddly work heh.

No I haven't run it through. I mean you see my getEndX() and getEndY() which grab the last node's X and Y - or at least it should. But in the program it stays the same, and I don't know why. Only works the first time, after that it stays the same.

Thanks.

A dequeue is the STL version of a doubly linked list. It can be traversed in either direction. The payload is simply a pointer to whatever you want to store, organized into a struct or class.

That's incorrect. std::list is a doubly linked list. std::deque is a list of arrays.

But yeah, std::deque is the best way to go here. or just use std::queue, since that's what you really need. std::queue is a container wrapper that uses deque by default, under the hood.

That's incorrect. std::list is a doubly linked list. std::deque is a list of arrays.

My bad. That being the case, wouldn't std::list or even std::forward_list be the appropriate container? Random access isn't really necessary for this.

No for two reasons:

1) List has high overhead for creating and deleting nodes. Each list member in a list has an associated node data, and for relatively small containers, this is a large cost.

2) linked lists have poor cache performance. Nodes can be anywhere in memory, and unlike containers built on arrays, the processor cannot pre-fetch the next or previous node. Traversing a list is very slow. For this reason, even use cases that involve removing an element from the middle of a container can be faster for array based containers, despite the need to do a lot of copying, because the const of finding the element to remove is so high.

Therefore unless there is a need to maintain references to container members when an element is inserted and removed, linked lists should not be used without profiling. They can be slow even on large datasets.

// initialize a 4-length snake to these coordinates
dequeue<pair<int,int>> snake{{3,3},{3,4},(4,4},{5,4}};
// possible directions 0-up, 1-right, 2-down, 3-left
unsigned char snake_direction = 0;
// to move the snake one cell forward in current direction
snake.emplace_back(snake.back().first+{0,1,0,-1}[snake_direction],
    snake.back().second+{1,0,-1,0}[snake_direction]);
snake.pop_front();