Comments on: 6.7 — Introduction to pointers

By: Shreevardhan

Shreevardhan — Wed, 08 Jun 2011 09:22:48 +0000

No memory allocated. That is why it crashes.

By: zingmars

zingmars — Wed, 08 Jun 2011 00:00:23 +0000

Something must be wrong, because the first code in which you declare only one pointer crashes too.

By: capitanui

capitanui — Tue, 07 Jun 2011 12:28:01 +0000

I have a question …i cannot understand something.
I have this simple code :

int *pValue;
*pValue = 4;
cout<<*pValue;

It's all ok..it prints 4;

I i declare another one my program crushes and i cannot understand why since is the same thing.

int *pValue, *nValue;

*pValue = 4;
*nValue = 5;

cout<<*pValue<<*nValue;

By: Getting Started with OpenFrameworks | The choreography of color and code

Getting Started with OpenFrameworks | The choreography of color and code — Tue, 31 May 2011 02:22:35 +0000

[...] So within our ParticleEmitter declaration we’ve declared that we’re going to have an x and y value to position our emitter on the screen and a rotation value to rotate the emitter over time. We also declare three methods, setup, update, and draw that will define what our emitter will do every time the application cycles through a frame. Lastly we declare an Array called “p” that will store all of the Particles that are currently on the screen. The pointer syntax(*) that declares the “p” array is out of the scope of this article, however you can learn about pointers and how they work in C++ via this excellent tutorial here. [...]

By: SWEngineer

SWEngineer — Sat, 22 Jan 2011 16:29:00 +0000

Simple well explained tutorial.

Thanks a lot.

By: xian

xian — Thu, 02 Sep 2010 05:56:54 +0000

This is a wonderful tutorial – the examples here clearly step through all possible pointer/pointed-to configurations. Thanks so much!

By: baldo

baldo — Fri, 14 Aug 2009 18:44:49 +0000

00000000 is not the value. See this:

cout << &pnPtr << endl;  // will print the address of the pointer (0013FF60)
cout << pnPtr << endl;   // will print the address that the pointer points to (00000000)
cout << *pnPtr << endl;  // will print the value of the address that the pointer points to

Because the pointer is null, it is pointing to address 00000000. The address of the pointer is 0013FF60.

By: baldo

baldo — Fri, 14 Aug 2009 18:35:47 +0000

The if (pnPtr) test to see if the pointer is null. If it is a null pointer then the address it is pointing is 0 (false). If the pointer is allocated (not null) then pnPtr points to a address != 0 (which means true).

By: Simon Kazakov

Simon Kazakov — Sat, 30 May 2009 06:57:14 +0000

The statement is okey. Assigning an address to a pointer means that u tell the pointer: “Point to this address”. This is done with the “&”.

 int a = 10;
int *ptr = &a;
// the * is not a dereference operator. It is a pointer declaration.

U can change the value of the pointed object with “*”.

 *ptr = 8; // changes a to 8

The pointer itself is a variable that has an address. It is impossible to have a variable at 0000 0000.

By: Hamza K

Hamza K — Wed, 13 May 2009 00:58:03 +0000

I don’t understand this statement, shouldn’t it be the other way around?:

 int *pnPtr = 0;  // assign address 0 to pnPtr

“Note that in the last example, the * is not a dereference operator. It is a pointer declaration. Thus we are assigning address 0 to pnPtr, not the value 0 to the variable that pnPtr points to.”

When I use the following code:

 int * pnPtr = 0;
cout << &pnPtr << endl;
cout << pnPtr << endl;

I get the output
0013FF60
00000000

surely the address is 0013FF… and the value is 000?

Many thanks for the tutorials though, they’re amazing, you’re a saint!