CPP Arrays and the Free Store

Using objects in arrays

• Any object, whether built-in or user defined, can be stored in an array.
• Accessing member data in an array of objects is a two-step process.
  1. Identify the member of the array by using the index operator ([ ]).
  2. Add the member operator (.) to access the particular member variable.

  Cow Farm[6];
  int i;
  for (i = 0; i < 6; i++){
  // The Farm[i] returns the object of a Cow
     Farm[i].setAge(2*i +1);
  }

Declaring Arrays on the Free Store.

• As for any object, you can declare an array of object on the free store with the new keyword.

  Cow *pFarm = new Cow[500];  // pFarm is a pointer to an array of 500 Cow objects
  Cow *pCow = pFarm;          // pCow points to pFarm[0]
  pCow->setAge(10);           // set pFarm[0] to 10
  pCow++;                     // advance to pFarm[1]
  pCow->setAge(20);           // set pFarm[1] to 20

• Be aware of that:

  Cow   pOne[50];             // Is an array of 50 Cow objects
  Cow * pTwo[50];             // Is an array of 50 pointers to Cow objects
  Cow * pThree = new Cow[50]; // Is a pointer to an array of 50 Cow objects
  

  Please remember that pOne and pThree have instances of Cow, but pTwo is only an array with no Cow object instance.
• You find an program example in the Aggregation and Delegation session.