[iSteve]

Author:iSteve/ Srinabh Jha
Difficulty:Novic
Title:Classes and Objects
Previous:[Tutorial] [C++GDK] C++ basics.
Next:Coming soon
Made for SA-MP forums


Alright, for those who don't know, you can write your gamemodes ( or codes ) for samp in C/C++ using Zeex's GDK.
In this tutorial i would be teaching you basics of C++, which you can implement in your gamemodes.

Class.

A class is a user defined data type, a class can hold data members and member functions, with their access specifier.
By default a class's access specifier is Private.
A class is terminated by a semi column ";"

PHP Code:

eg:
class test
{
    class members and member functiins;
}; 


Access Specifiers.

These declare the visiblity of the members of a user defined data type.
Private members can not be accessed by anything other than a friend( will come back to this later) or a member of that class.
Protected members has the same visiblity as that of a private one, but the difference lies in inheritance ( will be discussed later).
Public members can be accessed by other members of the class.

Object

An object is an instance of a class, or a variable of a class.
Eg

PHP Code:

class TEST
{
    int a;
};
int main()
{
    TEST ob;
} 


Accessing member functions or member data from an object.

To access a function in a class using an object, we can use the object with a dot "." and then the function name.

eg:

PHP Code:

class TEST
{
    public:int a;
    void hello()
    {
        cout<<"Hello world\n";
    }
};
int main()
{
    TEST obj;
    obj.a=1;//initializes the value of a as 1
    obj.hello()//prints Hello world on the terminal.
} 


Scope resolution operator"::"

Expanding functions outside the class
A scope resolution operator is "::".It can be used to expand member function outside the class
Eg:

PHP Code:

class A
{
    public:void print();
};
void A::print()
{
    cout<<"Hello world";
} 


Friend Functions

A friend function is an external function which can be declared friend to a class.The friend function can access private, protected as well as the public members of the class it is a friend to.
A friend function is not a member of the class it is declared a friend to.
Eg

PHP Code:

class A
{
    int a=10;
    public:friend int frnd(A);//
};
int frnd(A x)
{
    return A.a;
}
int main()
{
    A ob1;
    int x;
    x=ob1.frnd();//x = 10
} 


Friend Classes

A class can be declared as a friend to another class, this class can thus access the member functions and member data of the class declared friend to.
NOTE: if class B is a friend to class A, does not mean that class A is a friend to class B.
Eg:

PHP Code:

class A
{
    public:
    void out()
    {
        cout<<"Hello\n";
    }
    friend class B;
};
class B
{
    public:void output()
        {
            out();//accessing the out() function of the class A in class B 
        }
};
int main()
{
    B ob1;
    ob1.output();//prints Hello
}