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Pointers and Structures

Started by dinner_at_seven May 19, 2003 at 11:13 PM 8 replies 600+ views

Original Post

May 19, 2003 at 11:13 PM

Hello all, I was just wondering how I could go about solving a small problem I am having with pointers and structures. I have this in a .h file of mine: typedef struct { int xpos int ypos Particles particles } ENEMY; ENEMY enemy[10]; (particles being a structure that i have made up) so when i am trying to reference this from a function in my c file - such as this, and want to make a nother call to a function from within in this function i need a pointer to the particles within the strcuture normally i would just go like this MakeParticles(&particles) but when i try to go like this: MakeParticles(enemy[0].particles) this does not work. So i was wondering how i can go about getting a pointer to the structure. Thanks in advance.

Alpha_ProgDes

May 19, 2003 at 11:28 PM


typedef struct 
{
int xpos
int ypos
Particles particles
}

ENEMY;

ENEMY enemy[10];

void makeparticles (Particles*); //expecting a struct Particles

int main ()
{
   makeparticles (&  enemy[0].particles);
   //... other stuff
}

void makeparticles (Particles *initParticles)
{
   *(initparticles).x;
   //or 
   initparticles->x;
   // blah blah
}

mostly you'll have to post some code so we can see what the mistake is. but that's how you do it... afaik.

[edited by - Alpha_ProgDes on May 19, 2003 12:29:26 AM]

edit: Jambolo caught my oversight. thank you.

[edited by - Alpha_ProgDes on May 20, 2003 2:57:42 AM]

kdogg

May 19, 2003 at 11:53 PM

I'd just pass a pointer to the entire struct [EDIT: the ENEMY struct, that is]. That would be the simplest way and there would be no speed loss.

[edited by - kdogg on May 20, 2003 12:46:30 PM]

JohnBolton

May 20, 2003 at 1:47 AM

MakeParticles(&enemy[0].particles)

Sander

May 20, 2003 at 2:05 AM

You could also make the MakeParticles() function a part of the Particle class and call

Emeny[0].particles.MakeParticles();

I think that''s the most elegant solution, but It depends on what your MakeParticles() function does.

Alpha_ProgDes

May 20, 2003 at 2:22 AM

kdogg:
do you suggest this?

      
makeParticles (&(enemy[0]).particles);

//i'm guessing it has the same properties(?) as this:


makeParticles (*(enemy[0]).particles);

i too thought of the passing ENEMY* but then figured he wouldn't want to rewrite his function (whether a total or near-total rewrite, i'm unsure).

smarechal: from his code i figure he's using only C, not C++.
so i believe we should give him the most elegant C solution

edit: code tags looked funny.

[edited by - Alpha_ProgDes on May 20, 2003 3:26:05 AM]

[edited by - Alpha_ProgDes on May 20, 2003 3:27:01 AM]

JohnBolton

May 20, 2003 at 3:15 AM

quote:
Original post by kdogg
That will look for the particles member of the address of the struct enemy[0], i.e., it won't compile.

kdogg, you are wrong. According to the C precedence rules &x[ n ].y is the same as &( ( x[ n ] ).y )

quote:

...
MakeParticles(enemy[0].particles)
this does not work. So i was wondering how i can go about getting a pointer to the structure.

The answer is:

MakeParticles( & enemy[0].particles )

[edited by - Jambolo on May 20, 2003 4:16:44 AM]

LordDeath

May 20, 2003 at 11:05 AM

Jambolo is correct.

kdogg

May 20, 2003 at 11:46 AM

my bad.

dinner_at_seven

May 20, 2003 at 7:58 PM

Thanks for all the help guys - had to go home and check my code and yes
the answer was
MakeParticles(&enemy[0].particles) just like it should have been - at one
stage i did have that and it wasnt working cause of another reason. Thanks
again for the quick response.

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