Cosine

Overheal

How do you implement the inverse of cosine (in C++)?

fasty

#include <math.h>
double acos (double x);

Or if you actually want to write your own function, erm... get a maths book! I've forgotten the details!

Overheal

thats just what i needed thanks

(stupid cosine rule)

edit: that would happen to be overload for use with float by any chace?

fasty

Yeah man, there's a float version

float __cdecl acosf( float );

Don't worry about the __cdecl bit.

Just take a look in math.h and you'll see all it can do for you! Mine is in C:\Program Files\Microsoft Visual Studio 9.0\VC\include

Overheal

Awww.... reading? pfft. I have deadlines to meet and chicken to eat!

thanks

fasty

I know, reading up on stuff is crazy talk. My coworkers laugh their heads off when I read the docs and look at source. Real men don't read the instructions apparently!

Overheal

Basically, my code is crashing with an exception saying I am trying to access memory location 0 while i am trying to add an object to a list.

global:

BrickController * pBrickCon; // object that controls a list of Bricks (for Breakout Game)

main(){

...

pBrickCon->Setup(...);

...

    while (myEngine->isRunning()){
       myEngine->drawScene();
       pBrickCon->Update();
       ...
    }
}

using tle::ISprite;

class Brick : public ISpriteWrapper 
{
public:
    Brick(string const & imageName, int x, int y, int id);
    bool Update(Ball *pBall);
};

class BrickController
{
private:
    int xCols, yRows, spacing;
    SLinkedList<Brick*, SListIterator<Brick*>> brickList;
public:
    
    BrickController();
    void Setup(int SCREEN_WIDTH, int SCREEN_HEIGHT, int spacing); //setup list structure of bricks
    bool Update(Ball * pBall); //update bricks.
    ~BrickController(){}
};

Brick::Brick(string const & imageName, int x, int y, int id) :
ISpriteWrapper(imageName, x, y, id) {}

BrickController::BrickController() {}

void BrickController::Setup(int SCREEN_WIDTH, int SCREEN_HEIGHT, int spacing)
{
    ImageResource::s_spriteType = BRICK;
    brickList.insertFirst(new Brick(ImageResource::BRICK_NAME,0,0,ImageResource::s_spriteType));
    SListIterator<Brick*> iter = brickList.begin();
    int width = (*iter)->d_width + spacing; // x-distance between 2 bricks
    int height = (*iter)->d_height + spacing; // y-distance between 2 bricks
    Vector spawn( width + spacing, 0); // A marker used to determine where the next brick is placed.

    for( ; (spawn.x < (SCREEN_WIDTH - width )); spawn.x + width ){
        for( ; (spawn.y < ((SCREEN_HEIGHT / 2) - height + spacing)); spawn.y + height ){
            brickList.insertLast(new Brick(ImageResource::BRICK_NAME,spawn.x,spawn.y,ImageResource::s_spriteType));
        }
    }
}

the crash is occuring at the insertFirst.

fasty

Make sure all the parameters you're passing to the Brick constructor are valid. nesting the new Brick line in insertFirst makes things look tidier, but harder to debug. Is it really insertFirst that's causing the error?

Brick* testBrick = NULL;
testBrick = new Brick(ImageResource::BRICK_NAME,0,0,ImageResource::s_spriteType);
if(testBrick != NULL) brickList.insertFirst(testBrick)
else // do some error handling here

At a guess, I'd have the problem is with ImageResource::BRICK_NAME or more than likely ImageResource::s_spriteType. What type of string is it?

Overheal

Nope I found the error when I tested my Update function by hard-writing it into main: I had never initalised a new BrickController object into the brickCon pointer. Whoopsie!

main(){

..

pBrickCon = new BrickController(); // is what i needed

pBrickCon->Update(...); // somehow this managed to call anyway, and it crashed when it tried to load the class definition of the list.. or something like that.

fasty

Good old null pointers!

Get into the habit of initialising pointers to zero and before you dereference them, make sure it's value is != 0;

MyClass* pMyClass = 0;

// some code, including we assume pMyClass = new MyClass() buy maybe you forgot!

if(pMyClass != 0) pMyClass->SomeFunction();
else // error