Coding: Dynamically Defined Variables

// Object Structure
enum ObjType { OT_Static, OT_Anim };

typedef struct {
int x, y;
enum ObjType type;
void *image_data;
} ObjectType;

typedef struct {
int width;
int height;
} StaticImageType;

typedef structure {
int width, height;
int tile_width, tile_height;
int min_frame, current_frame, max_frame;
} AnimatedImageType;

// Create 100 Objects
ObjectType Objs[100];

// Initialization Functions
void Init_Static_Object(int id, int width, int height)
{
StaticImageType *tempData = malloc(sizeof(StaticImageType));
Objs[id].width = width;
Objs[id].height = height;
Objs[id].image_data = tempData;
}

void Init_Static_Object(int id, int width, int height)
{
StaticImageType *tempData = malloc(sizeof(StaticImageType));
tempData->width = width;
tempData->height = height;
Objs[id].type = OT_Static;
Objs[id].image_data = (void*)tempData;
}
void Init_Anim_Object(int id, int width, int height)
{
AnimatedImageType *tempData = malloc(sizeof(AnimatedImageType));
tempData->width = width;
tempData->height = height;
Objs[id].type = OT_Anim;
Objs[id].image_data = (void*)tempData;
}

void Draw_Object(int id)
{
  if (Objs[id].type == OT_Static)
  {
    StaticImageType *tempData = (StaticImageType*)Objs[id].image_data;
    //Do drawing static
  }else if (Objs[id].type == OT_Anim)
  {
    AnimatedImageType *tempData = (AnimatedImageType*)Objs[id].image_data;
    //Do drawing with animation
  }
}

#include 
#include 

// Object Structure

typedef struct {
  int x, y;
  void *image_data;
} ObjectType;

typedef struct {
  int width;
  int height;
} StaticImageType;

typedef struct {
  int width, height;
  int tile_width, tile_height;
  int min_frame, current_frame, max_frame;
} AnimatedImageType;

// Create 100 Objects
ObjectType Objs[100];

// Initialization Functions
void Init_Static_Object(int id, int width, int height)
{
  StaticImageType *tempData = malloc(sizeof(StaticImageType));
  tempData->width = width;
  tempData->height = height;
  Objs[id].image_data = (void*)tempData;
}

void Init_Anim_Object(int id, int width, int height)
{
  AnimatedImageType *tempData = malloc(sizeof(AnimatedImageType));
  tempData->width = width;
  tempData->height = height;
  Objs[id].image_data = (void*)tempData;
}

int main()
{
  
  Init_Static_Object(0,64,64);
  Init_Anim_Object(1,64,64);
  
  printf("Object 0: (%d,%d)->(%d,%d)",Objs[0].x,Objs[0].y,Objs[0].image_data->width,Objs[0].image_data->height);
  printf("Object 1: (%d,%d)->(%d,%d)",Objs[1].x,Objs[1].y,Objs[1].image_data->width,Objs[1].image_data->height);
  
  return 0;
  
}

#include 
#include 

// Object Structure

typedef struct {
  int x, y;
  void *image_data;
} ObjectType;

typedef struct {
  int width;
  int height;
} StaticImageType;

typedef struct {
  int width, height;
  int tile_width, tile_height;
  int min_frame, current_frame, max_frame;
} AnimatedImageType;

// Create 100 Objects
ObjectType Objs[100];

// Initialization Functions
void Init_Static_Object(int id, int width, int height)
{
  StaticImageType *tempData = (StaticImageType *) malloc(sizeof(StaticImageType));
  tempData->width = width;
  tempData->height = height;
  Objs[id].image_data = (StaticImageType *)tempData;
}

void Init_Anim_Object(int id, int width, int height)
{
  AnimatedImageType *tempData = (AnimatedImageType *) malloc(sizeof(AnimatedImageType));
  tempData->width = width;
  tempData->height = height;
  Objs[id].image_data = (AnimatedImageType *)tempData;
}

int main()
{
  
  Init_Static_Object(0,64,64);
  Init_Anim_Object(1,64,64);
  
  printf("Object 0: (%d,%d)->(%d,%d)",Objs[0].x,Objs[0].y,Objs[0].image_data->width,Objs[0].image_data->height);
  printf("Object 1: (%d,%d)->(%d,%d)",Objs[1].x,Objs[1].y,Objs[1].image_data->width,Objs[1].image_data->height);
  
  return 0;
  
}

typedef struct {
  int width;
  int height;
} StaticImageType;

typedef struct {
  int x, y;
  StaticImageType* image_data;
} ObjectType;

Quote
LordAshes
With all due respect, I know you are just trying to help, but I believe I answered this in this thread above.

The reason why this is not possible is because the structure that image_data points to is not known at design time. In the simplified example above, it can point to either the startic or dynamic image structure. In my real code it can point to one of a hundred different structures. The decision as to which structure it points to is made at runtime.

I am fairly sure I have the pointer address correct (i.e. using memory commands I could probably read the structure data) but I would like it to recognize the structure so I can use references like objs[0].image_data->width.

This means the design time type needs to be generic (i.e. void) but at run-time this needs to be changed to one of the structure types.

(typing via PPC)

#include 
#include 

#define IMAGE_TYPE_STATIC 0
#define IMAGE_TYPE_ANIMATED 1

typedef struct {
  int width;
  int height;
  int type;
  // these fields are only valid if type==IMAGE_TYPE_ANIMATED
  int tile_width;
  int tile_height;
  int min_frame;
  int current_frame;
  int max_frame;
} ImageType;

// Object Structure

typedef struct {
  int x, y;
  ImageType *image_data;
} ObjectType;

// Create 100 Objects
ObjectType Objs[100];

// Initialization Functions
void Init_Static_Object(int id, int width, int height)
{
  ImageType *tempData = (ImageType *)malloc(sizeof(ImageType));
  tempData->width = width;
  tempData->height = height;
  tempData->type = IMAGE_TYPE_STATIC;
  Objs[id].image_data = tempData;
}

void Init_Anim_Object(int id, int width, int height)
{
  ImageType *tempData = (ImageType *)malloc(sizeof(ImageType));
  tempData->width = width;
  tempData->height = height;
  tempData->type = IMAGE_TYPE_ANIMATED;
  // set the other fields?
  Objs[id].image_data = tempData;
}

int main()
{
  
  Init_Static_Object(0,64,64);
  Init_Anim_Object(1,64,64);
  
  printf("Object 0: (%d,%d)->(%d,%d)",Objs[0].x,Objs[0].y,Objs[0].image_data->width,Objs[0].image_data->height);
  printf("Object 1: (%d,%d)->(%d,%d)",Objs[1].x,Objs[1].y,Objs[1].image_data->width,Objs[1].image_data->height);
  
  return 0;
  
}

Quote
scanff
Sorry I missed that part. Sounds like a hard way of doing it. Does you're code need to be strict C, this type of problem is exactly why C++ was created. You can use polymorphism and derive from a base class, much easier than casting voids and adding checks to see what the actual data type is.

Quote
tueidj
Completely off the top of my head, might have typos/stupid mistakes:

{Code removed to reduce space}

Takes a bit more memory, but this is probably the simplest way unless you want to move the type field into ObjectType and make image_data a union.

#include 
#include 

// Object Structure

#define OBJECT_TYPE_STATIC_IMAGE 0
#define OBJECT_TYPE_ANIMATED_IMAGE 1
// more defines for other object types go here

typedef struct {
  int x, y;
  int type;
  union {
    StaticImageType *StaticImageData;
    AnimatedImageType *AnimatedImageData;
    // other type pointers go here
  };
} ObjectType;

typedef struct {
  int width;
  int height;
} StaticImageType;

typedef struct {
  int width, height;
  int tile_width, tile_height;
  int min_frame, current_frame, max_frame;
} AnimatedImageType;

// Create 100 Objects
ObjectType Objs[100];

// Initialization Functions
void Init_Static_Object(int id, int width, int height)
{
  StaticImageType *tempData = (StaticImageType *)malloc(sizeof(StaticImageType));
  tempData->width = width;
  tempData->height = height;
  Objs[id].type = OBJECT_TYPE_STATIC_IMAGE;
  Objs[id].StaticImageData = tempData;
}

void Init_Anim_Object(int id, int width, int height)
{
  AnimatedImageType *tempData = (AnimatedImageType *)malloc(sizeof(AnimatedImageType));
  tempData->width = width;
  tempData->height = height;
  Objs[id].type = OBJECT_TYPE_ANIMATED_IMAGE;
  Objs[id].AnimatedImageData = tempData;
}

int main()
{
  int i;
  Init_Static_Object(0,64,64);
  Init_Anim_Object(1,64,64);
  
  for (i=0;i<2;i++) {
    switch (Objs.type) {
      case OBJECT_TYPE_STATIC_IMAGE:
          printf("Object %d: (%d,%d)->(%d,%d)\n", i,Objs.x,Objs.y,Objs.StaticImageData->width,Objs.StaticImageData->height);
          break;
      case OBJECT_TYPE_ANIMATED_IMAGE:
          printf("Object %d: (%d,%d)->(%d,%d)\n", i,Objs.x,Objs.y,Objs.AnimatedImageData->width,Objs.AnimatedImageData->height);
          break;
      default:
          printf("I don't know wtf this object is.\n");
    }
  }
  
  return 0;
  
}

Quote
tueidj
Well you need to at least give an accurate example if you want people to improve it. Let's try again.

Quote
LordAshes
The reason why this is not possible is because the structure that image_data points to is not known at design time. In the simplified example above, it can point to either the startic or dynamic image structure. In my real code it can point to one of a hundred different structures. The decision as to which structure it points to is made at runtime.

Quote
tueidj
Do you expect C to somehow magically know what your structs will look like without defining them?

Quote
WikiFSX
That's it. If you want C to know about all ~500 types, you are going to have to program support for all of them. This isn't some scripting language where you just automagically throw things in variables.