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#ActualHonestDuane

Posted 09 February 2013 - 03:16 PM

You can also store the pointers as offsets from the start of a structure.

Then when you load this structure into memory, you can 'fixup' the pointers by adding the offset to the actual memory address of the start of the loaded structure and saving the result back, and voila, your pointers are valid again.

0 Start of structure1 Pointer to Chicken (offset 3)2 Pointer to Duck (offset 6)3 Chicken4 ..5 ..6 Duck7 ..8 ..

Or better explained in C code (And x-posted on my site)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Declare your basic struct.
typedef struct MyGameObject{
unsigned char hp;
char *name; // Doesn't matter what this is for our demo here.
} GameObject;

// Declare your game id type to make things easier later.
typedef unsigned long int GameObjectId;

// Declare the struct that contains all of the data.
typedef struct MyGameRealObject{
GameObjectId id;
GameObject gameObject;
} AllocatedGameObject;

// Function to build the allocated object.
// Param name should be allocated off the heap not the stack.
GameObject *BuildGameObject(char *name, unsigned char hp){
// Get our gameObjectId.
// Lets just Pretend the number is coming from a
// global singleton manager.
GameObjectId gameobjectIdNumber = 12345;

// Allocate enough memory for your new struct
// and a hidden game object id.
AllocatedGameObject *go = (AllocatedGameObject*)malloc(sizeof(AllocatedGameObject));

if(!go){
// barf how you like, this isn't meant to be complete.
}

go->id = gameobjectIdNumber;
go->gameObject.hp = hp;
go->gameObject.name = name;

GameObject *gameObjectToReturn = &go->gameObject;

return gameObjectToReturn;
}

// Function to get the full allocated object.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
AllocatedGameObject *GetAllocatedGameObject(GameObject *gameObject){

if(!gameObject){
return 0;
}

char *vhs = (char *)gameObject; // Makes our math easier.
AllocatedGameObject* allocated = (AllocatedGameObject*)(vhs - sizeof(GameObjectId));

return allocated;
}

// Get the gameObject's hidden id.
// param should be allocated off the heap not the stack or bad things will happen.
GameObjectId GetGameObjectId(GameObject *gameObject){
AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);

if(allocated){
return allocated->id;
}

return 0;
}

// Cleanup and destroy the allocated GameObject.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
// Per the above so should the game objects ->name.
void DestroyGameObject(GameObject *gameObject){
if(!gameObject){
return;
}

AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);

if(!allocated){
return;
}

allocated->id = 0;
allocated->gameObject.hp = 0;

if(allocated->gameObject.name){
size_t len = strlen(allocated->gameObject.name);
memset(allocated->gameObject.name, 0, len);
free(allocated->gameObject.name);
allocated->gameObject.name = NULL;
}

free(allocated);
}

int main(char* argv){
// Build game object
char *objectName = strdup("Scary Monster!");
GameObject *gameObject = BuildGameObject( objectName, 100 );
GameObjectId gameObjectId = GetGameObjectId(gameObject);

printf("\nId: %d\n", gameObjectId);
printf("Name: %s\n", gameObject->name);

// Always clean up after yourself.
DestroyGameObject(gameObject);

return 0;

}

#3HonestDuane

Posted 09 February 2013 - 03:16 PM

You can also store the pointers as offsets from the start of a structure.

Then when you load this structure into memory, you can 'fixup' the pointers by adding the offset to the actual memory address of the start of the loaded structure and saving the result back, and voila, your pointers are valid again.

0 Start of structure1 Pointer to Chicken (offset 3)2 Pointer to Duck (offset 6)3 Chicken4 ..5 ..6 Duck7 ..8 ..

Or better explained in C code (And x-posted on my site)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Declare your basic struct.
typedef struct MyGameObject{
unsigned char hp;
char *name; // Doesn't matter what this is for our demo here.
} GameObject;

// Declare your game id type to make things easier later.
typedef unsigned long int GameObjectId;

// Declare the struct that contains all of the data.
typedef struct MyGameRealObject{
GameObjectId id;
GameObject gameObject;
} AllocatedGameObject;

// Function to build the allocated object.
// Param name should be allocated off the heap not the stack.
GameObject *BuildGameObject(char *name, unsigned char hp){
// Get our gameObjectId.
// Lets just Pretend the number is coming from a
// global singleton manager.
GameObjectId gameobjectIdNumber = 12345;

// Allocate enough memory for your new struct
// and a hidden game object id.
AllocatedGameObject *go = (AllocatedGameObject*)malloc(sizeof(AllocatedGameObject));

if(!go){
// barf how you like, this isn't meant to be complete.
}

go->id = gameobjectIdNumber;
go->gameObject.hp = hp;
go->gameObject.name = name;

GameObject *gameObjectToReturn = &go->gameObject;

return gameObjectToReturn;
}

// Function to get the full allocated object.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
AllocatedGameObject *GetAllocatedGameObject(GameObject *gameObject){

if(!gameObject){
return 0;
}

char *vhs = (char *)gameObject; // Makes our math easier.
AllocatedGameObject* allocated = (AllocatedGameObject*)(vhs - sizeof(GameObjectId));

return allocated;
}

// Get the gameObject's hidden id.
// param should be allocated off the heap not the stack or bad things will happen.
GameObjectId GetGameObjectId(GameObject *gameObject){
AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);

if(allocated){
return allocated->id;
}

return 0;
}

// Cleanup and destroy the allocated GameObject.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
// Per the above so should the game objects ->name.
void DestroyGameObject(GameObject *gameObject){
if(!gameObject){
return;
}

AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);

if(!allocated){
return;
}

allocated->id = 0;
allocated->gameObject.hp = 0;

if(allocated->gameObject.name){
size_t len = strlen(allocated->gameObject.name);
memset(allocated->gameObject.name, 0, len);
free(allocated->gameObject.name);
allocated->gameObject.name = NULL;
}

free(allocated);
}

int main(char* argv){
// Build game object
char *objectName = strdup("Scary Monster!");
GameObject *gameObject = BuildGameObject( objectName, 100 );
GameObjectId gameObjectId = GetGameObjectId(gameObject);

printf("\nId: %d\n", gameObjectId);
printf("Name: %s\n", gameObject->name);

// Always clean up after yourself.
DestroyGameObject(gameObject);

return 0;

}

#2HonestDuane

Posted 09 February 2013 - 03:16 PM

You can also store the pointers as offsets from the start of a structure.

Then when you load this structure into memory, you can 'fixup' the pointers by adding the offset to the actual memory address of the start of the loaded structure and saving the result back, and voila, your pointers are valid again.

0 Start of structure1 Pointer to Chicken (offset 3)2 Pointer to Duck (offset 6)3 Chicken4 ..5 ..6 Duck7 ..8 ..

Or better explained in C code (And x-posted on my site)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Declare your basic struct.
typedef struct MyGameObject{
unsigned char hp;
char *name; // Doesn't matter what this is for our demo here.
} GameObject;

// Declare your game id type to make things easier later.
typedef unsigned long int GameObjectId;

// Declare the struct that contains all of the data.
typedef struct MyGameRealObject{
GameObjectId id;
GameObject gameObject;
} AllocatedGameObject;

// Function to build the allocated object.
// Param name should be allocated off the heap not the stack.
GameObject *BuildGameObject(char *name, unsigned char hp){
// Get our gameObjectId.
// Lets just Pretend the number is coming from a
// global singleton manager.
GameObjectId gameobjectIdNumber = 12345;

// Allocate enough memory for your new struct
// and a hidden game object id.
AllocatedGameObject *go = (AllocatedGameObject*)malloc(sizeof(AllocatedGameObject));

if(!go){
// barf how you like, this isn't meant to be complete.
}

go->id = gameobjectIdNumber;
go->gameObject.hp = hp;
go->gameObject.name = name;

GameObject *gameObjectToReturn = &go->gameObject;

return gameObjectToReturn;
}

// Function to get the full allocated object.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
AllocatedGameObject *GetAllocatedGameObject(GameObject *gameObject){

if(!gameObject){
return 0;
}

char *vhs = (char *)gameObject; // Makes our math easier.
AllocatedGameObject* allocated = (AllocatedGameObject*)(vhs - sizeof(GameObjectId));

return allocated;
}

// Get the gameObject's hidden id.
// param should be allocated off the heap not the stack or bad things will happen.
GameObjectId GetGameObjectId(GameObject *gameObject){
AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);

if(allocated){
return allocated->id;
}

return 0;
}

// Cleanup and destroy the allocated GameObject.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
// Per the above so should the game objects ->name.
void DestroyGameObject(GameObject *gameObject){
if(!gameObject){
return;
}

AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);

if(!allocated){
return;
}

allocated->id = 0;
allocated->gameObject.hp = 0;

if(allocated->gameObject.name){
size_t len = strlen(allocated->gameObject.name);
memset(allocated->gameObject.name, 0, len);
free(allocated->gameObject.name);
allocated->gameObject.name = NULL;
}

free(allocated);
}

int main(char* argv){
// Build game object
char *objectName = strdup("Scary Monster!");
GameObject *gameObject = BuildGameObject( objectName, 100 );
GameObjectId gameObjectId = GetGameObjectId(gameObject);

printf("\nId: %d\n", gameObjectId);
printf("Name: %s\n", gameObject->name);

// Always clean up after yourself.
DestroyGameObject(gameObject);

return 0;

}

#1HonestDuane

Posted 09 February 2013 - 03:15 PM

You can also store the pointers as offsets from the start of a structure.

 

Then when you load this structure into memory, you can 'fixup' the pointers by adding the offset to the actual memory address of the start of the loaded structure and saving the result back, and voila, your pointers are valid again.

 

0 Start of structure
1 Pointer to Chicken (offset 3)
2 Pointer to Duck (offset 6)
3 Chicken
4 ..
5 ..
6 Duck
7 ..
8 ..

 

Or better explained in C ode (And pre-posted on my site)

 


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
   
// Declare your basic struct.
typedef struct MyGameObject{
   unsigned char hp;
   char *name; // Doesn't matter what this is for our demo here.
} GameObject;
   
// Declare your game id type to make things easier later.
typedef unsigned long int GameObjectId;
   
// Declare the struct that contains all of the data.
typedef struct MyGameRealObject{
   GameObjectId id;
   GameObject gameObject;
} AllocatedGameObject;
   
// Function to build the allocated object.
// Param name should be allocated off the heap not the stack.
GameObject *BuildGameObject(char *name, unsigned char hp){
   // Get our gameObjectId.
   // Lets just Pretend the number is coming from a
   // global singleton manager.
   GameObjectId gameobjectIdNumber = 12345;
   
   // Allocate enough memory for your new struct
   // and a hidden game object id.
   AllocatedGameObject *go = (AllocatedGameObject*)malloc(sizeof(AllocatedGameObject));
   
   if(!go){
      // barf how you like, this isn't meant to be complete.
   }
   
   go->id = gameobjectIdNumber;
   go->gameObject.hp = hp;
   go->gameObject.name = name;
   
   GameObject *gameObjectToReturn = &go->gameObject;
   
   return gameObjectToReturn;
}

// Function to get the full allocated object.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
AllocatedGameObject *GetAllocatedGameObject(GameObject *gameObject){
 
   if(!gameObject){
      return 0;
   }
   
   char *vhs = (char *)gameObject; // Makes our math easier.
   AllocatedGameObject* allocated = (AllocatedGameObject*)(vhs - sizeof(GameObjectId));
   
   return allocated;
}
 
// Get the gameObject's hidden id.
// param should be allocated off the heap not the stack or bad things will happen.
GameObjectId GetGameObjectId(GameObject *gameObject){
   AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);
 
   if(allocated){
      return allocated->id;
   }
 
   return 0;
}
   
// Cleanup and destroy the allocated GameObject.
// param gameObject should be part of a AllocatedGameObject allocated off the heap.
// Per the above so should the game objects ->name.
void DestroyGameObject(GameObject *gameObject){
   if(!gameObject){
      return;
   }
   
   AllocatedGameObject* allocated = GetAllocatedGameObject(gameObject);
   
   if(!allocated){
      return;
   }
   
   allocated->id = 0;
   allocated->gameObject.hp = 0;
   
   if(allocated->gameObject.name){
      size_t len = strlen(allocated->gameObject.name);
      memset(allocated->gameObject.name, 0, len);
      free(allocated->gameObject.name);
      allocated->gameObject.name = NULL;
   }
   
   free(allocated);
}
   
int main(char* argv){
   // Build game object
   char *objectName = strdup("Scary Monster!");
   GameObject *gameObject = BuildGameObject( objectName, 100 );
   GameObjectId gameObjectId = GetGameObjectId(gameObject);
   
   printf("\nId: %d\n", gameObjectId);
   printf("Name: %s\n", gameObject->name);
   
   // Always clean up after yourself.
   DestroyGameObject(gameObject);
   
   return 0;

}


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