Dynamic Memory Allocation

	Variables explicitly allocated and deallocated at execution time by
	means of two special operators, new and delete.

The HEAP -- the Free Store

	A pool of memory locations reserved for allocation and deallocation
	of dynamic data.

    new <type>;
    new <type> [<int expr>];

    int * returnValue;
    returnValue = new int[40];    // Create an array of 40 integers

    delete ;
    delete [] ;

Memory leak

the loss of available memory space that occurs when dynamic data is allocated but never deallocated.

Inaccessible Object

a dynamic variable on the free store without any pointer pointing to it.

Dangling pointer

a pointer that points to a variable that has been deallocated.

Examples

int* ptr1 = new int;
int* ptr2 = new int;

*ptr2 = 44;
*ptr1 = *ptr2;

ptr1 = ptr2;	// what ptr1 originally pointed becomes inaccessible,
                //    should delete ptr1 first 

delete ptr2;	// ptr1 becomes dangling,
		//    can be avoided by : ptr2 = NULL;

Dynamic Data Examples

class Person {
public:
    string name;      // Person's name
    int age;          // Their age
};                    // Note the annoying semi-colon!!

    Person Me;           // Declare a person
    Me.name = "Chang";   // set their name
    Me.age = 25;         // and age

class Person {
public:
    string name;             // Person's name
    int age;                 // Their age
    Person * father;         // Pointer to father
    Person * mother;         //        and mother
};

  Person * Human;

  Human Alice, Bob;	     // is same as
                             //    Person * Alice, * Bob;     

Making new People

    Person * Alice;
    Alice = new Person;
    Alice->name = "Alice";   // is same as 
                             //    (*Alice).name = "Alice";
    Alice->age  = 20;        //    (*Alice).age  = 20;

We can make parents for Alice:

    Alice->father = new Person;
    Alice->mother = new Person;

And we could continue making ancestors ...

    (Alice->father)->father = new Person;
    ((Alice->father)->father)->mother = new Person;