Pointer type question

[MurrayL]

Can someone please explain the difference between these two variable declarations?

Code: AGS

Character *myCharacter = cEgo;
// and
AudioChannel* myChannel = aSound1.Play();

What is the effect of the asterisk being before the variable name as opposed to after the type, and vice versa?

[Khris]

There's no difference.
It's better form to use the latter because the asterisk is part of the type, not the name, but it doesn't matter to the compiler (which ignores whitespace outside of strings anyway).

It also becomes apparent if you define multiple pointers like so:

Code: ags

Character* enemy1, enemy2;

[MurrayL]

Ah, that's a relief.

I've always put the asterisk after the type, but I've seen a few forum posts (and I'm pretty sure there are even a few instances in the AGS manual) where people have done it the other way around. Wanted to make sure I wasn't doing something wrong!

[SpeechCenter]

In C you can have

Code: C

int *p1, i2;

or

Code: C

int* p1, i2;

which in fact defines the same thing, a pointer to int (p1) and an int (i2). Therefore many prefer the first when using C and maybe that's why you saw these examples.

However, since AGS doesn't really have pointers as in C, you cannot define

Code: AGS

Character *char1, *char2;

only

Code: AGS

Character* char1, char2;

So it's true that in AGS attaching the pointer to the type makes it clearer.

(By the way, all of my examples are actually considered bad style since it's much clearer to define variables in separate lines)

[selmiak]

You learn something new every day. This confused me too as the manual really does it the one way and sometimes even within the same paragraph also the other way. Thanks for this topic

[miguel]

Sorry for using this topic but it's related to pointers as well.

Header:

Code: AGS

struct herostats {
  int level;
  int exp;
  int max_exp;
  int health;
  int strenght;
  int dext;
  int atack_sword;
  int atack_mace;
  int atack_dagger;
  int atack_ranged;
  int atack_bolt;
  int armour;
  int defense;
  int luck;
  int mp;
  int damage;
  String name;
  String class;
  Character* Char;
};

Code: AGS

import herostats stHero;

Main Global:

Code: AGS

herostats stHero;

Code: AGS

export stHero;

I found that I can use without problems something like:

Code: AGS

stHero.Char.LockView(6);
      stHero.Char.Animate(2, 5, eOnce, eBlock);

But in a while loop, on a array attached to the struct, I get a null pointer when using the .Char reference.
Header:

Code: AGS

struct badguystats {
  int level;
  int health;
  int strenght;
  int dext;
  int atack_sword;
  int atack_ranged;
  int atack_magic;
  int atack_bolt;
  int armour;
  int defense;
  int luck;
  int mp;
  int damage;
  String name;
  String class;
  Character* Char;
};
import badguystats stbandit[3];

Main:

Code: AGS

badguystats stbandit[3];
export stbandit;

Function that returns null pointer:

Code: AGS

function enemydetection() {
  int closestEnemy = -1;
  int maxRange = 700;
  int xDiff; int yDiff; int enemyDistance;
  int i=0;
  while (i< Game.CharacterCount) {
  xDiff = stHero.Char.x - stbandit[i].Char.x;
  yDiff = stHero.Char.y - stbandit[i].Char.y;
  enemyDistance = xDiff*xDiff + yDiff*yDiff;
  if (enemyDistance < maxRange) {
    stbandit[i].Char.FollowCharacter(stHero.Char, 0, 0);
  }
i++;
  }
}

What did I do wrong?

[Crimson Wizard]

@miguel:
And how do you initialize Char pointer for stHero and stbandits? That's more important.
I think that problem is that you count 0th character as 0th bandit, which is probably not correct. This is only a guess, by I think that character with id = 0 is player? In which case you should start counting from ID=1, and access bandits as stbandit[i - 1] in that loop. This will also prevent from forcing player character to follow himself.

[miguel]

Crimson, thanks for your reply:
I initialize them at game start:

Code: AGS

function game_start() 
{
  mouse.Mode=eModePointer;
  //////////////////////////////////////////////////////////
stHero.Char=cHero;
stHero.armour=1;
stHero.atack_dagger=1;
stHero.atack_mace=1;
stHero.atack_ranged=1;
stHero.atack_sword=1;
stHero.class="Not defined";
stHero.defense=1;
stHero.dext=1;
stHero.exp=0;
stHero.health=40;
stHero.level=1;
stHero.luck=1;
stHero.max_exp=1000;
stHero.mp=0;
stHero.name="Unknown";
stHero.strenght=1;
////////////////////////////////////////////////////////////
stbandit[1].armour=2;
stbandit[1].atack_magic=0;
stbandit[1].atack_ranged=0;
stbandit[1].atack_sword=2;
stbandit[1].Char=cbandit;
stbandit[1].class="Bandit";
stbandit[1].defense=2;
stbandit[1].dext=1;
stbandit[1].health=55;
stbandit[1].level=1;
stbandit[1].luck=2;
stbandit[1].mp=0;
stbandit[1].name="Bandit";
stbandit[1].strenght=2;

I'm trying what you said right now...

Edit: still get a null pointer

[Crimson Wizard]

Ah. So you init bandit starting from 1st index, not 0. In which case my suggestion about using stbandit[i - 1] was wrong.
But in same case you must start the loop from i = 1, because stbandit[0] has uninitialized Char pointer (but use stbandit[ i ] as before).

[miguel]

Got it!
Now I get array out of bounds on line 7

Code: AGS

function enemydetection() {
  int closestEnemy = -1;
  int maxRange = 700;
  int xDiff; int yDiff; int enemyDistance;
  int i=1;
  while (i< Game.CharacterCount) {
  xDiff = stHero.Char.x - stbandit[i].Char.x;
  yDiff = stHero.Char.y - stbandit[i].Char.y;
  enemyDistance = xDiff*xDiff + yDiff*yDiff;
  if (enemyDistance < maxRange) {
    stbandit[i].Char.FollowCharacter(stHero.Char, 0, 0);
  }
i++;
  }
}

[Crimson Wizard]

.
Well, what you are doing there, is making a loop from 0 to X, where X = number of characters. And for every i you pick one item from "bandits" array.
Question is, is number of characters the same as "bandits" array size? Is there a "bandit" corresponding to every character, or only to a few? Maybe you shouldn't make a loop like that, but use different condition?

[miguel]

Okay, now I understand. My little dungeon seems to be working now.
I was using scripts from the forums (the one in this topic obviously) to base my code and every program is its own case.
I know I'll mess it up again but until then thank you very much Crimson.

I wish the tutorial for beginners in pointers was more friendly. The day I fully understand it I will make one for cavemen like me!