sprinkles


2009 Sep 6 • 2545
10 ₧

What's the purpose of pointers? Everyone uses them. Don't they refrence things?

SuperJer
Websiteman

2005 Mar 20 • 3883

A pointer a variable which contains an address.

For example let's say I have a byte-sized variable called pissant and it contains the value 0x42. The value 0x42 is stored at an actual position in memory, let's say 0xDEADBEEF.

So your memory looks kind of like this:



I put ?s in because like who the fuck knows what is in those other positions.

Now let's say you want to have a pointer to your pissant variable. Let's call it pointy. OK. It also has to have a position in memory. Let's store it at 0xDEADBEE8.

This is a 32-bit machine (I've decided) and therefore your pointer is got to have 4 bytes.

OK so like check out your memory now, kids:



You see that?!?!

The four bytes starting at 0xDEADBEE8 (which is the variable pointy) is a pointer to the position 0xDEADBEEF which just happens to be where pissant lives.

You got that?!!!

A pointer is a variable that contains the address of something... else.

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5404
57,583 ₧

Pointers are fun. See how quickly you can SegFault by iterating a pointer and writing over each memory address! I give a little into the moment like I'm standing at the edge (I know)
That no-one's gonna turn me 'round
Just one more step, I could let go

sprinkles


2009 Sep 6 • 2545
10 ₧

Sorry I should have been more specific. I know what a pointer is. I jus don't know what the point is for using them.
So when do you use a pointer? And why?

Killer-Duck
Homicidal Anatidae

2008 Mar 5 • 1169
633 ₧

See more at: http://en.wikipedia.org/wiki/Pointer_%28computing%29 QUACK! QUACK!

sprinkles


2009 Sep 6 • 2545
10 ₧

Can I have a real life example? I still can't get the concept.

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5404
57,583 ₧

Well, when you do myClass thingy = new myClass(), in C++ (as an example) you might do so with a pointer to thingy, rather than thingy itself. myClass might be really heavy on memory so it is better to move a pointer around and leave the class on the heap than it is to "directly" use the class.

These are the kind of issues that don't come up in managed languages, like Java and large wads of .NET. I give a little into the moment like I'm standing at the edge (I know)
That no-one's gonna turn me 'round
Just one more step, I could let go

SRAW
Rocket Man

2007 Nov 6 • 2376
601 ₧

That was indeed a very clear explanation dr...

sprinkles


2009 Sep 6 • 2545
10 ₧

So the pointer acts jus like the class?

buq25

2008 Jul 5 • 511
95 ₧

But less resource costing? Roses are red,
Violets are blue.
Shouldn't violets be violet,
and roses be rose?

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5404
57,583 ₧

In some sense. The pointer doesn't act like the class, it points to it. Because, you know, it's a pointer. I give a little into the moment like I'm standing at the edge (I know)
That no-one's gonna turn me 'round
Just one more step, I could let go

SuperJer
Websiteman

2005 Mar 20 • 3883

You don't need pointers. They are just one way of doing things.

In low level languages, and at the hardware level, pointers are everywhere, though. If you dig down enough, everything on a computer is about memory addresses.

Example use of a pointer:

Let's say you want to efficiently store the current state of the keyboard, and the previous state of the keyboard. In a game or something.

Let's say there's an API call GetKeyboardState( int array[255] ) to which you pass an array, and it fills it with a 0 or 1 at each position depending on whether each key is currently pressed down.

Let's make 2 arrays to hold the current and previous states:



Now let's make 2 pointers:



Now everytime we read a new keyboard state, swap where the pointers are pointing, and read in the new data.



This is somewhat efficient because you don't actually have to move the whole 255-element arrays at any time. You just switch the pointers.

Hope I didn't screw that up...

adhesive



2007 Sep 13 • 79
1,301 ₧

Ever send an array to another function?

Surprise, You secretly used pointers!
You actually sent &x[0] to work and the work function views int numbers[] as int* numbers. This way you can just send 4bytes (address of x[0]) to work instead of the whole array (4bytes * array length).
If you didn't use pointers you would have to send all elements to the work function, make a new array there, do the calculations, return all the modified elements to the function caller, and finally repopulate the original array. Try making a recursive program without pointers.

sprinkles


2009 Sep 6 • 2545
10 ₧

I'm not sure I understand what you mean by move.


??

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5404
57,583 ₧

Just read Wikipedia and have a play yourself. That's the best way to do it. I give a little into the moment like I'm standing at the edge (I know)
That no-one's gonna turn me 'round
Just one more step, I could let go

sprinkles


2009 Sep 6 • 2545
10 ₧

http://en.wikipedia.org/wiki/St._Bernard_(dog)

?

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5404
57,583 ₧

http://en.wikipedia.org/wiki/Pointer_(dog_breed) I give a little into the moment like I'm standing at the edge (I know)
That no-one's gonna turn me 'round
Just one more step, I could let go

Rockbomb
Dog fucker (but in a good way now)

2009 Nov 13 • 2026

AHAHAHAHAHAHAHAHAHAHAHAHA

SRAW
Rocket Man

2007 Nov 6 • 2376
601 ₧

SPRINKLES GOT PWNED