What enables an object to initialize itself when it is created?

Answer 1

Object initialisation is taken care of by the object's constructor(s). Initialisation is generally done during the initialisation stage of the constructor (immediately before the body of the constructor). Complex members such as pointers can be initialised to NULL in the initialisation stage. If new memory must be allocated to a member pointer, do it in the body of the constructor. Remember to clean up all allocated memory in the class destructor.

class cMyClass

{

public: // Construction.

cMyClass(); // Default constructor.

cMyClass(const cMyClass & MyClass); // Copy constructor.

cMyClass(const int i); // Overloaded constructor.

~cMyClass(); // Destructor.

private: // Member variables.

int m_int; // An integer.

int * m_pInt; // A pointer to an integer.

};

// Default constructor.

cMyClass::cMyClass(): // Colon indicates initialisation stage.

m_int( 0 ), // Comma-separated list of members to be initialised.

m_pInt( NULL ) // Optional; m_pInt will be initialised in the body.

{

// Body of the constructor:

// m_int is currently initialised to the value zero.

// m_pInt currently points to NULL.

m_pInt = new int;

*m_pInt = 0;

// m_pInt now points to new memory containing the value zero.

// Initialisation is complete!

}

// Copy constructor

cMyClass::cMyClass(const cMyClass & MyClass): // Initialisation

m_int( MyClass.m_int ), // Member list

m_pInt( NULL )

{

// m_int is initialised to the value of MyClass.m_int

// m_pInt currently points to NULL.

m_pInt = new int; // Allocate new memory.

*m_pInt = *MyClass.m_pInt; // Deep-copy the value.

// m_pInt now points to a copy of the value pointed to by MyClass.m_pInt.

// Initialisation is complete!

}

// Overloaded constructor

cMyClass::cMyClass(const int i): // Initialisation.

m_int( i ), // Member list.

m_pInt( NULL )

{

// m_int is initialised to the value of i.

// m_pInt currently points to NULL.

m_pInt = new int;

*m_pInt = 0;

// m_pInt now points to new memory containing the value zero.

// Initialisation is complete!

}

// Destructor. cMyClass::~cMyClass()

{

// Clean up allocated memory.

if( m_pInt ) delete m_pInt;

}