How to initialize static member variable of abstract class

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Hi,
I have scenario like this.

class Books
{
protected:
   static int BookId;
   int    b;
   ;
public:
   void Init () = 0;
   SetVal (int val);
   ;
}

class Novel : public Books
{
public:
   Init (int val) {b = val}
}

I want to initialize int BookId to 0. How this can be done in efficient way without killing OOP concept ?

Posted 21-Jul-11 14:39pm

Member 8097131

Updated 21-Jul-11 15:27pm

walterhevedeich

v2

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Emilio Garavaglia · Answer 1 · 2011-07-21T22:12:00

Solution 3

Admitting you he a books.h file containing the class Books declaration,
you need a CPP file (books.cpp can be good) that does

#include "books.h"
int Books::BookId = 0;

It is basically the same as venkatmakan [^]did in his solution, but that way result in a "multiple definition" linker error, in case the "books.h" file is included by more "CPP" files.

Posted 21-Jul-11 22:12pm

Emilio Garavaglia

Comments

Harrison H 22-Jul-11 19:53pm

This is the only answer.

వేంకటనారాయణ(venkatmakam) · Answer 2 · 2011-07-21T19:53:00

Solution 2

will this give error?

C#

class Books
{
protected:
   static int BookId;
   int    b;
public:
   virtual void Init () = 0; //syntax is corrected
   int SetVal (int val);
};
int Books::BookId = 0;

Posted 21-Jul-11 19:53pm

వేంకటనారాయణ(venkatmakam)

Christian Graus · Answer 3 · 2011-07-21T14:49:00

Solution 1

A constructor ?

Apparently I need to write more, to post my answer.

Posted 21-Jul-11 14:49pm

Christian Graus

Comments

Member 8097131 21-Jul-11 21:35pm

there are two problems in this solution
(1) Abstract class can not have object of it.
(2) Object of derived class will call constructor of Abstract class and initialize it to zero. So, every time object created, "a" will become zero. but i want a single time initialization thats why i kept it "static".

Sergey Chepurin 22-Jul-11 5:48am

From MSDN (http://msdn.microsoft.com/en-us/library/c8whxhf1.aspx:)"A class that contains at least one pure virtual function is considered an abstract class. Classes derived from the abstract class must implement the pure virtual function or they, too, are abstract classes".