Question

Earlier i moved some data to a singleton object, GamePropertiesManager. In this class i define a variable called _gameSpeed and in the class constructor i use an intialisation list to set it to 1 as default.

In another class i have an update loop that, (outside of my control), will always update as frequently as possible. I intended to, and successfully used a ‘speed’ variable to slow down the updating. This worked by, say, setting it to 2 the game would only update every other call to onUpdate.. I might make sense if you look at the contents of PlayState::onUpdate() below (I posted the whole cpp under the advice of a commenter):

#include "PlayState.hpp"
#include "PlayerController.hpp"
#include "AIController.hpp"

#include <stdlib.h>
#include <time.h>

//testin
#include <iostream>

/// Implement PlayState

PlayState::PlayState()
{}
PlayState::~PlayState()
{}

bool PlayState::onCreate()
{
   _gameProperties = GamePropertiesManager::GetInstance();

   _frameCounter = 0;
   application.addKeyListener( *this );
   _collisionFlag = false;

   //snakes created, intialising a pointer to fruit managaer, controller and opposing snake
   _player1 = new Snake();
   _player2 = new Snake();
   _player1->Initialise(&_fruitManager, new PlayerController(_player1), _player2);
   _player2->Initialise(&_fruitManager, new AIController(_player2), _player1);

   return true;
}
bool PlayState::onDestroy()
{
   return true;
}

void PlayState::onEntry()
{
   //seed to randomise food positions later
    srand ( time(0) );
}

void PlayState::onExit()
{

}

void PlayState::onUpdate()
{
   //TODO: rename _snake speed and maybe make it global gamespeed
   ++_frameCounter; //FrameCounter can be used to slow the snake down
   if(_frameCounter >= _gameProperties->GetGameSpeed())
   {

       //updating
       _fruitManager.UpdateFruits();
      _player1->Update(&_collisionFlag);
      _player2->Update(&_collisionFlag);

      if (_collisionFlag)
         application.setState("gameover");

      _frameCounter = 0;
   }

}

void PlayState::onRender( Canvas& c )
{
   _player1->Draw(c);
   _player2->Draw(c);

    _fruitManager.DrawFruits(c);
}

bool PlayState::onKey (const KeyEvent& key)
{
if( key.key_state == KeyEvent::KB_DOWN ){

    switch (key.key){
         case KeyEvent::KB_ESC_KEY:
            application.exit();
            break;
        case 'p':
            application.setState("pause");
            break;
      }
}
   return true;
}

_gameProperties is a pointer to a/the GamePropertiesManager which i assign in PlayState::onCreate(), when my class PlayState is first created..

The actual GamePropertiesManager class looks like this:

#include "GamePropertiesManager.hpp"

GamePropertiesManager* GamePropertiesManager::_instance = NULL;

GamePropertiesManager* GamePropertiesManager::GetInstance()
{
   if (!_instance) //instance not yet created
      _instance = new GamePropertiesManager();

   return _instance;
}

void GamePropertiesManager::Destroy()
{
   delete _instance;
   _instance = 0;
}

GamePropertiesManager::GamePropertiesManager() :
   _gameMode(PLAYERVSCOM), _player1Name("Player 1"), _player2Name("Player 2"),
      _player1Score(0), _player2Score(0), _matchSurvivor("NONE"), _gameSpeed(1)
{

}

unsigned int GamePropertiesManager::GetGameSpeed()
{
   return _gameSpeed;
}

My problem is that, when i change the value of _gameSpeed in the initialisation list to any value aside from (1) my program crashes at runtime. I find this particularly odd as i was previously comparing _frameCounter to both hard coded values other than 1 and a speed variable set to values other than 1 and the program ran fine as expected. Any ideas about the problem?

Hope i explained myself well enough, appreciate your help!

Answer 1

The reason is almost certainly because for any value other than 1, in the first call to PlayState::onUpdate the if check won’t run, most likely leaving something uninitialized.