A pointer is a way of accessing a variable.
For instance:

int a = 5;
cout << a;

This creates a variable named a, and outputs it's value to the screen. Note that you have actually CREATED an int here.

int * b; //A POINTER to an int
b = &a //& means (memory address of)

This creates a POINTER to an int, and sets it to point to a. Note that you have NOT created an int here: just a pointer to one.

You can now do this:

cout << *b;

This will output the value of the variable pointed to by b (in other words a). The * is necessary when using pointers as otherwise it simply outputs the address of b.

You can also change the value of a through b.

*b = 8;

This sets the value of a to 8. (because b points to a).

I dunno if this is helping, but I'll just plod on anyway...

What you must understand is that when you create a pointer to an int (int * b), you are NOT creating an int. (It's the same with any other data type too) You are simply creating a name by which you can refer to an int. A pointer MUST point to something before it can be used.

int * b;
*b = 5;

This will not work, because b does not point to anything. You may not get an error, but it doesn't work

Now, as for why you might use pointers...

      void double(int x){ //Doubles the value of x x *= 2;}void main(){ int x = 5; double(x); cout << x << endl;}  

You might think that when the value of x is cout'ed, it would be ten, but it' not. It's still 5. This is because when you called double(x), it created a duplicate of x and passed it to double. Any changes made to x inside double were performed on the duplicate. So when you come back to main, x is still 5. We can fix this by using pointers, though. Instead of passing a duplicate of x into double, we are going to pass the MEMORY ADDRESS of x (a pointer). This will allow double to directly change the x in main.

  void double(int * x) //Now passes an int POINTER instead of value{ //Doubles the value of x *x *= 2;}void main(){ int x = 5; int * y = &x //Creates a pointer to x double(y); cout << x << endl;}  

You should find that x is now 10.

I know that pointers can be confusing, and also that someone trying to explain pointers can be doubly confusing, but I hope this has helped :D

P.S. This took some time to type, and I apologize if someone else has replyed in the meantime.

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

I finally got it all together...
...and then forgot where I put it.

Edited by - AdmiralBinary on November 19, 2001 5:02:51 PM

Edited by - AdmiralBinary on November 19, 2001 5:04:03 PM

Tszafran, that basically uses a pointer in the background, it just hides it from you . References must always point to a valid variable, they can''t be NULL (a good and bad thing). They also cannot point to a dynamically allocated place in memory. Arrays are also treated as pointers.


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