Question

An array of class objects is similar to an array of some other data type. To create an array of Points, we write

Point parray [4];

To access the object at position i of the array, we write

parray [i]

and to call a method on that object method, we write

parray [i]. methodName (arg1 , arg2 , ...) ;

To initialize an array of objects whose values are known at compile time, we can write

Point parray [4] = { Point (0 ,1) , Point (1 ,2) , Point (3 ,5) , Point (8 ,13) };

We can also allocate an array of objects dynamically using the new operator (this implicitly calls the default constructor of each new Point):

Point * parray = new Point [4]; 1.2 Static members and variables

Static data members of a class are also known as “class variables,” because there is only one unique value for all the objects of that class. Their content is not different from one object of this class to another.

For example, it may be used for a variable within a class that can contain a counter with the number of objects of the class that are currently allocated, as in the following example:

1. # include <iostream >

2. using namespace std ;

3. class CDummy

4. {

5. public :

6. static int n;

7. CDummy () { ++n; }

8. ~CDummy() { --n; }

9. };

10. int CDummy ::n = 0;

11. int main ()

12. {

13. CDummy a;

14. CDummy b [5];

15. CDummy * c = new CDummy ;

16. cout << a .n << "\n" ; // prints out 7

17. delete c;

18. cout<< CDummy ::n << "\n"; //

19. return 0;

20. }

In fact, static members have the same properties as global variables, but they can only be referenced via the class: either in class methods, via a class instance (someObject.staticVariable, or via the className::variable construct.

Because these variables are global, if we were to initialize them in a header file we could end up with that initialization being compiled multiple times (once per time we include the header). To avoid this, we only include a static member’s “prototype” (its declaration) in the class declaration, but not its definition (its initialization). This is why line 10 above is necessary, and why if we were to provide a header file for CDummy, we would still need to put line 10 in a separate .cpp file. If you get linker errors saying a static int is undefined, check to see whether you’ve included a line like line 10 in a .cpp file.

Classes can also have static member functions – that is, member functions which are associated with the class but do not operate on a particular class instance. Such member functions may not access non-static data members. For instance, we might replace CDummy above with the following class definition:

prints

out 6

class CDummy

{

private :

static int n;

public :

CDummy () { ++n; } ~CDummy() { --n; }

static int getN () { return n;} };

getN could then be called as c –> getN() or CDummy::getN().

Answer 1

Hi,

Yes you can invoke the static methods like shown in the description.

Below is the sample code to show you how to invoke:

----------------------

#include<iostream >
using namespace std;

class CDummy
{
private :
    static int n;
public :
    CDummy ()
    {
        ++n;
    }

    ~CDummy()
    {
        --n;
    }

    static int getN ()
    {
        return n;
    }
};

int main()
{
    CDummy a;
    CDummy b[5];
    CDummy * c = new CDummy ;
    cout << CDummy::getN() << "\n" ;
    delete c;
    cout << c->getN() << "\n";
    return 0;
}

-------------

Search Project Build Debug Fortran wxSmith Tools Tools+ Plugins DoxyBlocks Settings Help main2.cpp x 2 4 25 26int main) 27 pr 28 CDummy ai 29 CDummy b[5] 30 CDummy c - new CDummy; cout << CDummy: :getN () <<"n"i delete c cout << c->getN( << "\n"; 31 32 34 return 0; 35 36 Logs & others イ) Code: :Blocks x | 4 search results f Build messages x | A CppCheck X·) CppCheck messages x·) Cscope cooc Build log Debugger x >、 x x Process terminated with status -1073741510 (0 minute (s), 4 second (s))

Hope this helps.