CODEWITHSUNDEEP
c++
alxcyl
alxcyl

Reputation: 2722

Changing a private member variable does not affect the whole class

I have a class, in it is a private member variable called which is an int. For some reason, if I change its value in a method (on the constructor, for example), it will change just fine. But if I change it on a different method and use printf to output what its contents are on yet another different method, the value is not carried over and is changed into a very very large number.

Header:

class Fruit {
   private:
      int m_fruitState; // 0 = IDLE, 1 = GROWING, 2 = READY, 3 = FALLEN, 4 = ROTTEN
      int m_fruitTimer;

    public:
       Fruit ( );

       int getFruitState( ); // Returns m_fruitState
       void setFruitState( int fState );

       void growFruit( CCTime dt ); // Called every 1 second (CCTime is a cocos2d-x class)
    };

CPP

#include "Fruit.h"

Fruit::Fruit( ) {
   // Set other member variables
   this -> setFruitState( 0 );  // m_fruitState = 0
   this -> m_fruitTimer = 0;
   this -> m_fruitSprite -> schedule( schedule_selector( Fruit::growFruit ), 1.0 ); // m_fruitSprite is a CCSprite (a cocos2d-x class). This basically calls growFruit() every 1 second
}

int getFruitState( ) {
   return this -> m_fruitState;
}

void setFruitState( int state ) {
   this -> m_fruitState = state;
}

void growFruit( CCTime dt ) {
   this -> m_fruitTimer++;
   printf( "%d seconds have elapsed.", m_fruitTimer );
   printf( "STATE = %d", this -> m_fruitState ); // Says my m_fruitState is a very big number

   // This if condition never becomes true, because at this point, m_fruitState = a very big number
   if ( this -> getfruitState( ) == 0 ) { // I even changed this to m_fruitState == 0, still the same
      if ( this -> m_fruitTimer == 5 ) { // check if 5 seconds have elapsed
         this -> setFruitState( 1 );
         this -> m_fruitTimer = 0;
      }
   }
}

And then on the main, I make an instance of MyClass.

I have no idea why that happens. Why does C++ do that and how do I fix it? Thanks in advance.

Upvotes: 0

Views: 2658

Answers (2)

molbdnilo
molbdnilo

Reputation: 66441

The "selector" argument to schedule should be a SEL_SCHEDULE, where

typedef void(CCObject::* SEL_SCHEDULE)(float)

i.e it should be a member function of a CCObject.
It is also supposed to be a member of the object you call schedule on, otherwise the target when it's called will be wrong.

I suspect that this

this -> m_fruitSprite -> schedule( schedule_selector( Fruit::growFruit ), 1.0 );

causes a call to Fruit::growFruit with this pointing at the sprite, not the fruit, which leads to all kinds of unpleasantness.
(Note that schedule_selector does a C-style cast, which means that it's inherently unsafe. Don't use it.)

Upvotes: 3

David Schwartz
David Schwartz

Reputation: 182819

     changeInt( int newInt );       // Assume newInt = 5

Remove the int from the above line.

  void doSomething( ); {

Remove the ; from the above line.

Update: Now you're missing a ; from the end of the header file. Fixing all the obvious bugs (that would likely keep it from even compiling), it works fine for me. Either there's still a difference between the code you pasted and the real code, or you've found a compiler bug.

Constructor: myInt = 0
changeInt( int ) : myInt = 5
After constructor and calling changeInt(), myInt = 5

Upvotes: 3

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