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Templates 689

19

Static Members and Templates ......................................................................

A template can declare static data members. A unique set of static data is created for

each class type that can be created from the template. That is, if you add a static member

to the Arrayclass (for example, a counter of how many arrays have been created), you

have one such member per type: one for all the arrays of Animals and another for all the

arrays of integers. Listing 19.7 adds a static member and a static function to the Array

class.

LISTING19.7 Using Static Member Data and Functions with Templates

0: #include <iostream>

1: using namespace std;

2:

3: const int DefaultSize = 3;

4:

5: // A trivial class for adding to arrays

6: class Animal

7: {

8: public:

9: // constructors

10: Animal(int);

11: Animal();

12: ~Animal();

13:

14: // accessors

15: int GetWeight() const { return itsWeight; }

16: void SetWeight(int theWeight) { itsWeight = theWeight; }

17:

18: // friend operators

19: friend ostream& operator<< (ostream&, const Animal&);

20:

21: private:

22: int itsWeight;

23: };

24:

25: // extraction operator for printing animals

26: ostream& operator<<

27: (ostream& theStream, const Animal& theAnimal)

28: {

29: theStream << theAnimal.GetWeight();

30: return theStream;

31: }

32:

33: Animal::Animal(int weight):

34: itsWeight(weight)

35: {