pointer initializatin

laczfinador · 01-18-2009, 05:40 AM

Hello there!
I am puzzled by a question lately, to wich I can't find an answer. What is the difference between the next pointer initialization methods:

Code:

int* pointer_name=NULL

and

Code:

int *pointer_name=NULL

I undestand, that the second one is the "standard" way of initializing a pointer, or at least that is how the tutorial on this website shows it, but what does the first one mean?

As I was searching the web for answers, I found another interesting example, where the pointer was initialized like this:

Code:

int * pointer_name=NULL

This was supposed to have some sort of special meaning, but I did not quite understand it, and I can't find the website now for further studying. I would be glad if someone could explain to me all these things about pointer initialization.

Big thanks in advance for everyone, reading this.

zacs7 · 01-18-2009, 05:49 AM

They mean exactly the same thing, it's a matter of style. I prefer the third one personally.

kermit · 01-18-2009, 06:55 AM

Just keep in mind that doing

Code:

int* p1, p2;

Does not declare two pointers, as if int* was a new type declaration. You could use a typedef to make an alias if you wanted to, but that is another story. If you want to declare two pointers, you have to do something like this:

Code:

int* p1, *p2;

or

Code:

int* p1, * p2;

Whatever you end up doing, try to be consistent in your use of it.

laczfinador · 01-18-2009, 07:19 AM

Hm... I am trying to understand how does the next function works. It is from a SDL game programming tutorial.

Code:

SDL_Surface *load_image(char filename[])
	{
	SDL_Surface* loadedImage=NULL;
	SDL_Surface* optimizedImage=NULL;

	loadedImage=SDL_LoadBMP(filename);
	if(loadedImage!=NULL)
		{
		optimizedImage=SDL_DisplayFormat(loadedImage);
		SDL_FreeSurface(loadedImage);
		}
	return optimizedImage;
	}

As you can see, both methods are used in this function definition - but why? Is this really just a matter of style or does it make some crucial difference if I put the asterisk to another position? As far as I tested, the program runs and compiles fine, when I play around with the asterisks, so - can it be, that the author of the tutorial wasn't consistent enough?

Thanks for the answers so far!

Elysia · 01-18-2009, 07:58 AM

http://www.research.att.com/~bs/bs_faq2.html#whitespace
Bjarne "explains" the difference between the two styles.
I prefer the first one, and find the 3rd one acceptable, as well.

MK27 · 01-18-2009, 08:54 AM

I like the 2nd one because it makes the most sense, and you can consider it the same as dereferencing

laczfinador · 01-18-2009, 08:55 AM

Now, that is the kind of answer I was looking for! Thanks a lot everyone, for helping me out!

Elysia · 01-18-2009, 08:59 AM

Quote:

Originally Posted by MK27

I like the 2nd one because it makes the most sense, and you can consider it the same as dereferencing

The second one makes absolutely no sense to me, whatsoever...

**laserlight** · 01-18-2009, 11:20 AM

Quote:

Originally Posted by laczfinador

can it be, that the author of the tutorial wasn't consistent enough?

Yes, there is a minor inconsisteny in style there.

kermit · 01-18-2009, 11:36 AM

Quote:

Originally Posted by Bjarne Stroustrup

placing the * closer to the name does not make this kind of error significantly less likely.

I disagree, but will grant that obviously my opinion as a programmer matters very little compared to someone as experienced as Stroustrup. That said, when I see

Code:

double *p, q;

it is immediately obvious to me that p is the pointer, and q is just a double.* For the original poster, seeing as you are posting this on the C board, have a look at this and this from the comp.lang.c FAQ. Steve Summit acknowledges the difference of opinion of the C FAQ and Stroustrups C++ FAQ.

I think Stroustrup makes a good point about declaring each pointer one per line. Again, whichever style one chooses, it is good to be consistent.

* - I would add that I am undoubtedly biased by the fact that C is the first language I learned and though I dabble in other languages (most recently I have taken up the task of becoming competent in C++ programming) it is still my 'primary' language. I have also gotten used to K&R style. Had I learned C++ first, I guess I would probably be more inclined to the 'Stroustrup style' of declaring a pointer with the asterisk next to the type rather than the name...

01-18-2009, 05:40 AM	#1
laczfinador Registered User Join Date: Dec 2008 Posts: 13	pointer initializatin - where to put the asterisk? Hello there! I am puzzled by a question lately, to wich I can't find an answer. What is the difference between the next pointer initialization methods: Code: int* pointer_name=NULL and Code: int pointer_name=NULL I undestand, that the second one is the "standard" way of initializing a pointer, or at least that is how the tutorial on this website shows it, but what does the first one mean? As I was searching the web for answers, I found another interesting example, where the pointer was initialized like this: Code: int pointer_name=NULL This was supposed to have some sort of special meaning, but I did not quite understand it, and I can't find the website now for further studying. I would be glad if someone could explain to me all these things about pointer initialization. Big thanks in advance for everyone, reading this.
laczfinador is offline

01-18-2009, 05:49 AM	#2
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,139	They mean exactly the same thing, it's a matter of style. I prefer the third one personally. __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim
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01-18-2009, 06:55 AM	#3
kermit ... Join Date: Jan 2003 Posts: 1,190	Just keep in mind that doing Code: int* p1, p2; Does not declare two pointers, as if int* was a new type declaration. You could use a typedef to make an alias if you wanted to, but that is another story. If you want to declare two pointers, you have to do something like this: Code: int* p1, p2; or Code: int p1, * p2; Whatever you end up doing, try to be consistent in your use of it. __________________ Got Ed? sys-sizes
kermit is offline

01-18-2009, 07:19 AM	#4
laczfinador Registered User Join Date: Dec 2008 Posts: 13	Well, here's an example... Hm... I am trying to understand how does the next function works. It is from a SDL game programming tutorial. Code: SDL_Surface load_image(char filename[]) { SDL_Surface loadedImage=NULL; SDL_Surface* optimizedImage=NULL; loadedImage=SDL_LoadBMP(filename); if(loadedImage!=NULL) { optimizedImage=SDL_DisplayFormat(loadedImage); SDL_FreeSurface(loadedImage); } return optimizedImage; } As you can see, both methods are used in this function definition - but why? Is this really just a matter of style or does it make some crucial difference if I put the asterisk to another position? As far as I tested, the program runs and compiles fine, when I play around with the asterisks, so - can it be, that the author of the tutorial wasn't consistent enough? Thanks for the answers so far!
laczfinador is offline

01-18-2009, 08:54 AM	#6
MK27 subminimalist Join Date: Jul 2008 Location: NYC Posts: 3,944	I like the 2nd one because it makes the most sense, and you can consider it the same as dereferencing __________________ Accuracy and integrity mean nothing if you don't make it past the censors...PYTHAGORAS
MK27 is offline

01-18-2009, 08:55 AM	#7
laczfinador Registered User Join Date: Dec 2008 Posts: 13	Thanks a lot! Now, that is the kind of answer I was looking for! Thanks a lot everyone, for helping me out!
laczfinador is offline

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