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Class

C++ classes are a tool for creating new types that can be used conveniently as builtin types The Fundamental idea in defining a new type is to separate the details of the implementation from the properties essential to the correc use of it

Brief Summary of classes

• A class is user-defined type
• A class consists of a set of members. The most common kinds of members are data members and member functions.
• Member functions can define the meaning of initialization, copy, move, and cleanup
• Members are accessed using .(dot) for objects and -> (arrow) for pointers.
• Operators, such as, +, !, and [], can be defined for a class
• A class is a namespace containing its members
• The public members provide the class's interface and the private members provide implementation details
• A struct is a class where members are by default public

Class Basics

class example

class X {
    private: // the representation (implementation) is private
        int m;
    public: // the user interface is public
        X(int i = 0): m{i} {} //a constructor (initialize the data member m)

        int mf(int i) { // a member function
            int old = m;
            m = i; //set a new value
            return old; // return the old value
        }
};
X var {7}; // a variable of type X, initialized to 7
int user(X var, X* ptr) {
    int x = var.mf(7); // access using .
    int y = ptr->mf(9); // access using ->
    int z = var.m; // error: cannot acces private member
}

1. Member functions

Functions declared within a class definition are called member functions

2. Default copying

a class object can be initialized with a copy of an obejct of its class

UserClass c1 = c0; // initialization by copy
UserClass c2 {d1}; // initialization by copy

3. Access Control

class is consist of two parts private part: can be used only by member functions, public part : interface to objects of class

4. class and struct

a struct is a class in which members are by default public struct S{}; is simply short hand for class S{public: };

5. Constructors

a constructor is recognized by having the same name as the class it self. programmers can declare a function with the explicit purpose of initializing objects.

class Date {
    int d, m, y;
    public:
    Date(int dd, int mm, int yy); // constructor
}

Date today = Date(23, 6, 1983); // OK
Date xmas(25, 12, 1990); // OK -> abbreviated form
Date my_birthday; //error: initializer missing
Date release1_0(10, 12) //error: third argument missing

Date today = Date{23, 6, 1982} // good!

I recommend the {} notation over the () notation for initializing, because it is explicit about what is being done

we could use default values directly as default arguments

class Date {
    int d, m, y;
    public:
    Date(int dd = today.d, int mm = today.m, int yy = today.y); // constructor
}

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