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passing structures as pointers through functions [ERROR] why?

aleisterbukowski · 2008-06-05T07:29:11

I'm wondering why my code isn't working as I want it to work. I have small header file. Called Particle.h #ifndef PARTICLE_H #define PARTICLE_H #include <math.h> #include <SDL\SDL.h> #include <SDL\SDL_gfxPrimitives.h> #define NUM 75 class Particle { public: Particle(); ~Particle(); void reset_particles(int n); void update(SDL_Surface* screen); void reset_all(); void attract(struct particles *A, struct particles *B); void render(SDL_Surface* screen); private: struct particles { double mass; double x, y; long oldX, oldY; long xp, yp; double ax, ay, vx, vy; }p[NUM]; int cx, cy; }; #endif #include "Particle.h" #include "Globals.h" Particle::Particle() { } Particle::~Particle() { } void Particle::attract(struct particles *A, struct particles *B) { double distance; double dist, distX, distY; double transX, transY; //increase the vector position of particle by it's velocity it's respected direction A->x += A->vx; A->y += A->vy; //calculate the distance between particles distX = A->x - B->x; distY = A->y - B->y; dist = distX*distX + distY*distY; if(dist != 0) { distance = 1/dist; } else dist = 0; transX = distX*distance; transY = distY*distance; //accelerate each particle acceleration (m*d) A->ax = -1 * B->mass * transX; A->ay = -1 * B->mass * transY; //increase velocity by acceleration value A->vx += A->ax; A->vy += A->ay; //scale position to the screen A->xp = cx + A->x; A->yp = cy + A->y; } //reset a number of particles void Particle::reset_particles(int n) { p[n].mass = 0.001; p[n].ax = 0; p[n].ay = 0; p[n].xp = 0; p[n].yp = 0; p[n].x = rand() % width/4; p[n].y = rand() % height/4; p[n].vx = 0; p[n].vy = 0; } void Particle::reset_all() { int n; cx = width/2; cy = height/2; for(n=0; n<NUM; n++) resetparticles(n); } void Particle::update(SDL_Surface* screen) { int n; int i; //erase old particle for(n=0; n<NUM; n++) { circleColor(screen, p[n].oldx, p[n].oldy, 5, 33); //apply gravity between every particle for(i=0; i<NUM; i++) { if(i != n) attract(&p[n], &p); } //reset particle if it gets to far away if((p[n].xp < 0) || (p[n].xp > 600) || (p[n].yp < 0) || (p[n].yp > 400)) reset_particles(n); //plot new particle circleColor(screen, p[n].xp, p[n].yp, 5, 33); //keep track of current position p[n].oldX = p[n].xp; p[n].oldY = p[n].yp; } //draw primary partice circleColor(screen, p[0].xp, p[0].yp, 5, 33); } I'm working with the book Game Programming All in One, and it uses Allegro to program by examples games. That's fine, I'm just trying to see how particles work, and how easy/difficult it is to make a particle system, and within chapter 2 there's a particle system, so I make it in Allegro no problem. I tried to make it myself in SDL, and I get Particle.cpp c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(13) : error C2511: 'void Particle::attract(Particle::particles *,Particle::particles *)' : overloaded member function not found in 'Particle' c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.h(13) : see declaration of 'Particle' c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(70) : error C3861: 'resetparticles': identifier not found c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(81) : error C2039: 'oldx' : is not a member of 'Particle::particles' c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.h(30) : see declaration of 'Particle::particles' c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(81) : error C2039: 'oldy' : is not a member of 'Particle::particles' c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.h(30) : see declaration of 'Particle::particles' c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(86) : error C2664: 'Particle::attract' : cannot convert parameter 1 from 'Particle::particles *' to 'particles *' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(94) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(94) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(102) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data c:\documents and settings\c.s. finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(102) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data Generating Code... is there a special way of calling structures as pointers that I'm not aware of yet ?

General and Gameplay Programming Programming

Started by aleisterbukowski June 05, 2008 04:21 AM

12 comments, last by Morrandir 15 years, 10 months ago

aleisterbukowski

146

Author

June 05, 2008 06:15 AM

Quote:Original post by Mathmo
EDIT: sorry about the double post

Hey, I'm busy working on it.

So here are my options right now.

First I'm reprogramming the class you suggested, and then if both attempts fail I'll try to make attract() a private function, since yes update() is the only one that calls it.

I would just quickly change that to private, however, I'm in the middle of debugging some smaller issues, since I no longer get that ugly debug message that started this post.

I'll keep you'll updated.

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Molle85

172

June 05, 2008 06:28 AM

Just don't nestle the structs within eachother ;)
Declare struct particles before the class.

fishmd

122

June 05, 2008 07:25 AM

your original problem was that you had the declaration of the struct after you used in a function. You can't do that in c or c++. Things must be declared before you use them.

class Particle{private:struct particles; <-----forward declerationpublic:	Particle();	~Particle();		void reset_particles(int n);	void update(int* screen);	void reset_all();	void attract(particles *A, particles *B);	void render(int* screen);private:	struct particles	{		double mass;		double x, y;		long oldX, oldY;		long xp, yp;		double ax, ay, vx, vy;	}p[NUM];	int cx, cy;};

this should compile however there's no point to making that an inner struct, and a private one at that.

[Edited by - fishmd on June 5, 2008 10:25:14 AM]

Morrandir

304

June 05, 2008 07:29 AM

You can keep the nested struct declaration if you really want to.

Your member function declaration should look like this:

void attract(particles *A, particles *B);

Your member function definition should look like this:

void Particle::attract(Particle::particles *A, Particle::particles *B){  // ...}

If you fixed the other typos you had there (you mistyped some of your variable names), then this should work fine.

EDIT: fishmd is right about the declaration order, I wonder why the compiler didn't complain about using an undeclared type.

passing structures as pointers through functions [ERROR] why?

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