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Tuesday, December 04, 2007

Classes and Structures in C++

In C, a structure (struct) gives us the ability to organize similar data together. You may wonder what I said. It is so in C, this is because structure is one of the few things which is more or less entirely different in the two languages (C and C++).

In C++, the role of structures is elevated so much as to be same as that of a class. In C, structure could only include data as variables and arrays but in C++ they can also include functions, constructors, destructors etc. and in fact everything else that a class can. Knowing this, it wouldn’t be wrong to say that in C++, structures are an alternate way of defining a class. However there are some differences.

Look at the following code:


  // First difference between a class
  // and a structure in C++
   
  // define a structure
  struct mystruct
  {
    char name[25];
    int id_no;
  };

  void main()
  {
    mystruct a;
    // in C, it is necessary to
    // include the struct keyword

    // Example:
    // struct mystruct a;

    ...
    ...
    ...
  }

In C, we must declare an object of a structure by using the keyword struct but in C++ it is optional to do so (just like a class).

Another difference is the fact that all the data or functions inside a struct are public by default contrary to a class, inside which scope is private by default.

It is obvious from the following code:


  // Second difference between a class
  // and a structure in C++

  // define a structure
  struct mystruct
  {
    // public by default
    // So convenient to start with
    // public declarations

    void func1();
    void func2();
    ...
    ...

  private:
  // now private
    int data1;
    int data2;
    ...
    ...
  };

  // define a class
  class myclass
  {
    // private by default
    int data1;
    int data2;
    ...
    ...

  public:
  // now public
    void func1();
    void func2();
    ...
    ...
  };

While you’ve got the power, you should not define a class as a struct since it is not a good practice. Structures and classes should be used as per their original purposes to avoid unnecessary complications and misunderstandings.

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3 comments:

  1. As i always say i am a big fan of this blog as well as the writer. i referred this site to some of coaching teachers and they appreciated it.

    ReplyDelete
  2. Thanks so much KarROX.
    It's totally my pleasure.

    ReplyDelete
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