On Mon, 11 Aug 2003 12:23:15 +0200, "Yame" <yame_conoces@hotmail.com>
wrote:
[color=blue]
>Here's my question: "Why are pointers so useful and why can't you just work
>with variables?"[/color]
Object-Oriented programming (eg, polymorphism) is not possible without
pointers. For instance, the following code defines an abstract
interface class (Dog) with one method (Bark). It also defines 2
specific types of dogs (Eskimo and Sheppard) that bark in different
ways. By instantiating an Eskimo and calling the Bark() method
through the Dog (base class) pointer, you are using polymorphism; a
cornerstone of object-oriented programming. If is not possible to
accomplish this behavior without using pointers (or references which
can be thought of as dereferenced pointers).
Here's some sample code, in 1 file which you can compile & run as-is:
#include <cstdlib>
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
class Dog
{
public:
virtual void Bark() const = 0;
};
class Eskimo : public Dog
{
public:
void Bark() const { cout << "Yip! Yip!" << endl; }
};
class Sheppard : public Dog
{
public:
void Bark() const { cout << "BOW WOW!!! BOW WOW!!!" << endl; }
};
int main()
{
// prologue
typedef vector<Dog*> Dogs;
Dogs vDogs;
Dogs::iterator itDog; // this is in function-scope to get around
a stupid MSVC bug; should be fine with all compilers
// build a vector of different types of dogs
vDogs.push_back(new Eskimo);
vDogs.push_back(new Sheppard);
// make all the dogs bark
for( itDog = vDogs.begin(); vDogs.end() != itDog; ++itDog )
{
// get the dog
Dog* pDog = *itDog;
// bark the dog
pDog->Bark();
}
// deallocate resources
for( itDog = vDogs.begin(); vDogs.end() != itDog; ++itDog )
{
// get the dog
Dog* pDog = *itDog;
// delete the dog object
delete pDog;
}
vDogs.clear();
// epilogue
return 0;
}
</dib>
John Dibling
Witty banter omitted for your protection
