What are data members and members function?

Answer 1

The correct terminology is member variables and member methods. They are both members of a class. The member variables are used to store an object's data, while the member methods are used to operate upon that data.

Answer 2

Data members are any containers that hold data, like variables or arrays inside object definitions. Member functions are methods or functions that are defined inside of objects and are generally used to manipulate data members and other object data.

Answer 3

A data member is a class member variable. That is, a variable that is declared to be a member of a class. The variable may be a primitive or complex data type (such as an object), or it may be a pointer to any data type.

The following examples show some of the ways member variables can be declared and initialised by a class. Note that member variables are typically declared private since it is normally only the class itself that requires direct access to the member variables.

class A

{

private:

int m_data; // member variable (primitive data type)

public:

A():m_data(0){} // default constructor

A(const A& rhs):m_data(rhs.m_data){} // copy constructor

A(const int rhs):m_data(0){set_data(rhs);} // overloaded constructor

int get_data()const{return(m_data);} // accessor (by value)

void set_data(int data){ // mutator with validation

if(data>-1000 && data<1000)

m_data = data; }

};

Note the purpose of class A is to store an int in the range -999 to +999 inclusive. If an invalid value is provided, or no value is provided, the class defaults the member to the value 0. The set_data() mutator method acts as the gatekeeper to the member variable, thus ensuring the data member is in a valid state at all times.

class B

{

private:

A m_object; // member variable (complex data type)

public:

B():m_object(){} // default constructor calling variable's default

constructor

B(const B& rhs):m_object(rhs){} // copy constructor

A get_object()const{return(m_object);} // accessor by value

void set_object(const A object){m_object=object;} // mutator

};

class C

{

private:

B* m_pobject; // member pointer (no access outside of this class)

public:

C():m_pobject(new B){} // default constructor instantiating pointer

C(const C& rhs):m_pobject(new B(*rhs.m_pobject){} // copy constructor (deep copy)

~C(){delete(m_pobject);} // destructor

C& operator=(const C& rhs){ // assignment operator

delete(m_pobject);

m_pobject = new B(*rhs.m_pobject);}

};

Note that class C does not expose the member variable because any code outside of the class could delete the pointer, thus invalidating the class. If you must expose a pointer via an accessor then it's often better to return a deep copy of the pointer (the caller is then responsible for storing and subsequently releasing the returned pointer). If you must return the pointer itself, ensure it is a constant pointer, even if the indirect value is to be treated as non-constant.

Answer 4

I think you meant member data and member function respectively. Both are the major elements of a class of object. You use the member functions (methods) to operate upon and extract data from the object. In other words, the methods provide the interface to the member data. What use it is inside the main program is ultimately determined by the purpose of the program and the type of objects you employ to arrive at the solution.