Thread: Structures, Unions and Classes

  1. #1
    Registered User
    Join Date
    Feb 2004

    Structures, Unions and Classes

    I'm confused with classes, unions and structures. I already read them in books but still I'm confused. Can anybody enlighten me?
    Flamers are worst than Newbies

  2. #2
    Confused Magos's Avatar
    Join Date
    Sep 2001
    In C++, struct == class except that stucts are public by default, while classes are private. They are basically a collection of dataypes mixed together.

    The members of a union share the same memory, so if you set one of the members you modify the others too.

    Give a man a fish and you feed him for a day.
    Teach a man to fish and you feed him for a lifetime.

  3. #3
    Hardware Engineer
    Join Date
    Sep 2001
    Keep reading books and the web. It's difficult to explain this stuff in a few sentances.

    UNION - I assume that unions are supposed to be used to make efficient use of memory. I've personally never seen unions used in a real program, only in books... I'm not saying that unions are never used... probably rarely used.

    STRUCTURE - Magos is right, there is little difference between structures and classes in C++. However, typically structures do not have member functions. This is because in C, a structure cannot have member functions. (There are no classes or member functions in C.)

    You can have a structure called Employee, and specific instances of that structure like Makoy and DougDbug. These structures can have variables like:


    CLASS - In object oriented programming, a specific instance of a class is an object. Makoy & DougDbug are objects. You can have the same member variables like:


    In addition, you can have member functions like:

    You cannot have functions like that in non-object oriented programming languages such as C. In C, functions would have to be outside the structure. You would have to pass a pointer to the structure into your IncreaseSalary() function. You would not have encapsulation.

    You can avoid structures, and always use classes if you wish.

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