Variables in a struct not updating

This problem is driving me crazy - I've just spent the past hour trying to figure out a problem that shouldn't be happening. I've narrowed it down to the z variable in the struct not being updated by the Update() function. I do know the function is being called because I put a printf command in there and it produced results. Any help would be great.

Edit: Tried having the compiler check for all warnings. Fixed a few things it reported but the problem remains.

Code:

/*
 * Starfield screensaver
 */
#include <stdio.h>
#include <time.h>
#include <vector>
using namespace std;

#include <GL/gl.h>
#include <GL/glu.h>
#include "SDL.h"

#define STARS_COUNT 1000

// Star
struct Star {
  float x;
  float y;
  float z;
  float brightness;
  
  Star() { Randomize(); };
  
  void Randomize() {
    x = (rand() % 10000 - 5000) / 1000.0;
    y = (rand() % 10000 - 5000) / 1000.0;
    z = (rand() % 100) / -100.0;
    brightness = (rand() % 10) / 7.5;
  };
  
  void Render() {
    glColor3f(brightness, brightness, brightness);
    glVertex3f(x, y, z);
  };
  
  void Update() {
    z += 0.1;
  };
};

// Initialises SDL and OpenGL
int InitVideo() {
  // SDL
  if (SDL_Init(SDL_INIT_VIDEO) < 0) { return 1; }
  
  SDL_WM_SetCaption("Starfield Screensaver", "Starfield Screensaver");
  
  SDL_GL_SetAttribute(SDL_GL_RED_SIZE,     5);
  SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE,   5);
  SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE,    5);
  SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
  
  const SDL_VideoInfo *videoinfo = SDL_GetVideoInfo();
  if (!videoinfo) { return 1; }
  
  if (SDL_SetVideoMode(0, 0, 0, SDL_OPENGL | SDL_FULLSCREEN) == NULL) { return 1; }
  
  // OpenGL
  glViewport(0, 0, videoinfo->current_w, videoinfo->current_h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  
  gluPerspective(60.0, (GLfloat)videoinfo->current_w / (GLfloat)videoinfo->current_h, 1.0, 10.0);
  
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  
  return 0;
}

// Handles the events from the keyboard and mouse
int ProcessEvents() {
  static    Uint32 movement;
  SDL_Event        event;
  
  while (SDL_PollEvent(&event)) {
    switch (event.type) {
      case SDL_QUIT:
      case SDL_KEYUP:
      case SDL_KEYDOWN:
      case SDL_MOUSEBUTTONUP:
      case SDL_MOUSEBUTTONDOWN:
        return 1;
      
      case SDL_MOUSEMOTION:
        if (movement > 5) { return 1; } else { movement++; }
        break;
      
      default:
        break;
    }
  }
  
  return 0;
}

// Renders the stars
void Render(vector <Star> stars) {
  glClear(GL_COLOR_BUFFER_BIT);
  glLoadIdentity();
  
  // Camera
  gluLookAt(0.0, 0.0, 5.0,
            0.0, 0.0,-5.0,
            0.0, 1.0, 0.0);
  
  // Render the stars
  glBegin(GL_POINTS);
    for (unsigned int index = 0; index < stars.size(); index++) {
      stars[index].Render();
    }
  glEnd();
  
  SDL_GL_SwapBuffers();
}

// Updates the stars
void Update(vector <Star> stars) {
  for (unsigned int index = 0; index < stars.size(); index++) {
    stars[index].Update();
  }
}

int main(int argc, char *argv[]) {
  if (InitVideo()) { return 1; }
  
  vector <Star> stars;
  for (int index = 0; index < STARS_COUNT; index++) { Star tempstar; stars.push_back(tempstar); }
  
  Uint8 running = true;
  while (running) {
    Render(stars);
    Update(stars);
    if (ProcessEvents() == 1) { running = false; }
    
    SDL_Delay(10);
  }
  
  SDL_Quit();
  return 0;
}

Originally Posted by Frobozz

I've just spent the past hour trying to figure out a problem that shouldn't be happening

... is it your inability to be less vague? Could you describe the problem? Can you not move along the Z-axis or do you get a funny picture when you do? What?

Shameless bump with a slight bit of info. I added printf statements once again only this time to see what happens with the data in the update routine and a modification of the update function to only update one star. It appears the star is resetting itself back to an old number after the function ends which makes me think the copy in the vector isn't being replaced with the new one.

This to one star:

Code:

void Update() {
  printf("%f\n", z);
  z += 0.1;
  printf("%f\n", z);
};

Produces:

Code:

-0.34
-0.24
-0.34
-0.24
-0.34
etc

makes me think the copy in the vector isn't being replaced with the new one.

You are passing the vector by value instead of by reference. Could that be the problem?

Hehe. That's embarrasing. Works now. Thanks a lot.

Here's the working code in case anyone is interested:

Code:

/*
 * Starfield screensaver
 */
#include <stdio.h>
#include <time.h>
#include <vector>
using namespace std;

#include <GL/gl.h>
#include <GL/glu.h>
#include "SDL.h"

#define STARS_COUNT 1000

// Star
struct Star {
  float x;
  float y;
  float z;
  float brightness;
  
  Star() { Randomize(); };
  
  void Randomize() {
    x = (rand() % 10000 - 5000) / 1000.0;
    y = (rand() % 10000 - 5000) / 1000.0;
    z = (rand() % 100) / -10.0;
    brightness = (rand() % 10) / 7.5;
  };
  
  void Render() {
    glColor3f(brightness, brightness, brightness);
    glVertex3f(x, y, z);
  };
  
  void Update() {
    z += 0.1;
    if (z >= 5.0) { Randomize(); }
  };
};

// Initialises SDL and OpenGL
int InitVideo() {
  // SDL
  if (SDL_Init(SDL_INIT_VIDEO) < 0) { return 1; }
  
  SDL_WM_SetCaption("Starfield Screensaver", "Starfield Screensaver");
  
  SDL_GL_SetAttribute(SDL_GL_RED_SIZE,     5);
  SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE,   5);
  SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE,    5);
  SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
  
  const SDL_VideoInfo *videoinfo = SDL_GetVideoInfo();
  if (!videoinfo) { return 1; }
  
  if (SDL_SetVideoMode(0, 0, 0, SDL_OPENGL | SDL_FULLSCREEN) == NULL) { return 1; }
  
  // OpenGL
  glViewport(0, 0, videoinfo->current_w, videoinfo->current_h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  
  gluPerspective(60.0, (GLfloat)videoinfo->current_w / (GLfloat)videoinfo->current_h, 1.0, 10.0);
  
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  
  return 0;
}

// Handles the events from the keyboard and mouse
int ProcessEvents() {
  static    Uint32 movement;
  SDL_Event        event;
  
  while (SDL_PollEvent(&event)) {
    switch (event.type) {
      case SDL_QUIT:
      case SDL_KEYUP:
      case SDL_KEYDOWN:
      case SDL_MOUSEBUTTONUP:
      case SDL_MOUSEBUTTONDOWN:
        return 1;
      
      case SDL_MOUSEMOTION:
        if (movement > 5) { return 1; } else { movement++; }
        break;
      
      default:
        break;
    }
  }
  
  return 0;
}

// Renders the stars
void Render(vector <Star> *stars) {
  glClear(GL_COLOR_BUFFER_BIT);
  glLoadIdentity();
  
  // Camera
  gluLookAt(0.0, 0.0, 5.0,
            0.0, 0.0,-5.0,
            0.0, 1.0, 0.0);
  
  // Render the stars
  glBegin(GL_POINTS);
    for (unsigned int index = 0; index < stars->size(); index++) {
      stars->at(index).Render();
    }
  glEnd();
  
  SDL_GL_SwapBuffers();
}

// Updates the stars
void Update(vector <Star> *stars) {
  for (unsigned int index = 0; index < stars->size(); index++) {
    stars->at(index).Update();
  }
}

int main(int argc, char *argv[]) {
  if (InitVideo()) { return 1; }
  
  vector <Star> *stars = new vector <Star>;
  for (int index = 0; index < STARS_COUNT; index++) { Star tempstar; stars->push_back(tempstar); }
  
  Uint8 running = true;
  while (running) {
    Render(stars);
    Update(stars);
    if (ProcessEvents() == 1) { running = false; }
    
    SDL_Delay(10);
  }
  
  SDL_Quit();
  return 0;
}

Once again, thanks for the help!

hmm... why pass by pointer?

Code:

// Renders the stars
void Render(vector <Star>& stars) {
  glClear(GL_COLOR_BUFFER_BIT);
  glLoadIdentity();
  
  // Camera
  gluLookAt(0.0, 0.0, 5.0,
            0.0, 0.0,-5.0,
            0.0, 1.0, 0.0);
  
  // Render the stars
  glBegin(GL_POINTS);
    for (unsigned int index = 0; index < stars.size(); index++) {
      stars[index].Render();
    }
  glEnd();
  
  SDL_GL_SwapBuffers();
}

// Updates the stars
void Update(vector <Star>& stars) {
  for (unsigned int index = 0; index < stars.size(); index++) {
    stars[index].Update();
  }

Originally Posted by Frobozz

Here's the working code in case anyone is interested:

did you write/download SDL.h yourself? Because all of the SDL parts give compile errors for me.