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AmiDARK
GCC, Dynamic structure creation method ?
Posted on: 2009/2/25 18:29    #1
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Hi,

In fact, I want to create dynamically objects that uses a structure.

Imagine a structure like this one :

typedef struct{
  BOOL Exist;
  float XPos, YPos, ZPos;
  float XRot, YRot, ZRot;
  float FOV;
  BOOL Backdrop;
  float RangeNear, RangeFar;
  float Left, Top, Right, Bottom;
 }ObjectType;


I want to have a function in my program that allocate a small memory for an object that'll use this structure and, the function must return the pointer to the freshly created object structure.

I'm not enough skilled in C to imagine how to do this.
Any one got an idea about this ?

Thank you.

Kindest Regards,
Freddix


Edited by freddix on 2009/2/25 19:21:59
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xeron
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/25 18:36    #2
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@freddix

ObjectType *AllocateObject( void )
{
  ObjectType newObj = NULL;

  newObj = IExec->AllocVecTags( sizeof( ObjectType ), TAG_DONE );
  if( !newObj ) return NULL;

  // Do any required initialisation

  return newObj;
}

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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/25 19:14    #3
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@xeron
Thank you for this small function.

I imagine that if I want to delete this object from memory, I'll have to do something like this :

*FreeObject( NewObjectType ){
  if ( NewObjectType <> 0 ){
    IExec->FreeVec( NewObjectType );
   }
 }


Am I wrong ?
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salass00
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/25 19:33    #4
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@freddix

In C it's "!=" instead of "<>".
void FreeObject( ObjectType *obj ){
  if ( obj != NULL ){
    IExec->FreeVec( obj );
  }
}


Actually as IExec->FreeVec() allows passing in a NULL pointer (in this case it will simply do nothing) you can just write:

void FreeObject( ObjectType *obj ){
  IExec->FreeVec( obj );
}

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Slash
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/25 19:36    #5
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@salass00

Quote:

salass00 wrote:

Actually as IExec->FreeVec() allows passing in a NULL pointer (in this case it will simply do nothing) you can just write:


Does it? You learn something new everyday... I've always checked if the memory pointed is NULL or not before IExec->FreeVec.
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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/25 19:37    #6
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@salass00
It's what I supposed .... but wasn't sure ...
Thank you.

If I'm not wrong, all this should be correct :

typedef struct{
  BOOL Exist;
  int Type;
  BOOL Hidden, Culling, Transparency, WireFrame, Fog, Ambient, Lights, Filtering;
  float XPos, YPos, YPos;
  float XRot, YRot, ZRot;
  float XScale, YScale, ZScale;
  float RGBRed, RGBGreen, RGBBlue;
 }Object3DType;

static Object3DType *Allocate3DObject( void );
static void Free3DObject( Object3DType *OldObject );

Object3DType *Allocate3DObject( void ){
  Object3DType *NewObject = NULL;
  NewObject = IExec -> AllocVecTags( sizeof( Object3DType ), TAG_DONE );
  if ( !NewObject ){
    return NULL;
   }
  return NewObject;
 }

void Free3DObject( Object3DType *OldObject ){
  if ( obj != NULL ){
    IExec -> FreeVec( OldObject );
   }
 }


Right ?


Edited by freddix on 2009/2/25 23:51:35
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Gazelle
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/25 22:12    #7
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@freddix

There should be an asterisk in the declaration of NewObject in the Allocate3DObject() function:

Object3DType *NewObject = NULL;

It's a pointer.
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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/26 0:00    #8
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@Gazelle
I've modified. is it correct now ?
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xeron
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/26 11:16    #9
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@freddix

Yes. A good tip is to initialise the structure to sensible defaults as much as possible in your constructor. Can save weird bugs and headaches later.
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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/26 13:58    #10
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@xeron
Do you think that handling the list per ranges can be good ?

For example :
Default is defined with 512 entries,
If more than 512, directly re-allocate 1024 entries,
if more than 1024, directly re-allocate 1536 entries,
if more than 1536, directly re-allocate to 2048 entries,
etc ...

Good idea ?
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LiveForIt
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/26 16:32    #11
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@freddix

typedef struct{

  void *last;
  void *next;

  BOOL Exist;
  int Type;
  BOOL Hidden, Culling, Transparency, WireFrame, Fog, Ambient, Lights, Filtering;
  float XPos, YPos, YPos;
  float XRot, YRot, ZRot;
  float XScale, YScale, ZScale;
  float RGBRed, RGBGreen, RGBBlue;
 }Object3DType;


If you add a next and last pointer you can add objects, so it becomes a list, note that there exist a node and list structure in exec already you can use, this enable you use the exec functions for this.

If you are making a multi threaded game or program, you should be thinking about some kind of lock for etch of objects, so that one thread does not modify the same object at the same time, it called writing a thread safe programs.
(NutsAboutAmiga)

Basilisk II for AmigaOS4
AmigaInputAnywhere
Excalibur
and other tools and apps.
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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/26 17:21    #12
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@LiveForIt
Thank you.

A friend just sent me an e-mail explaining linked-list too.
now I understand what I must do to handle objects dynamically.

Thank you all.

Kindest Regards,
Freddix
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salass00
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/27 11:37    #13
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@Slash

Quote:

Does it? You learn something new everyday... I've always checked if the memory pointed is NULL or not before IExec->FreeVec.


It does. It's even documented in the autodocs.

Same applies to many other functions, like DisposeObject(), DeleteMsgPort(), FreeSysObject(), Close(), DropInterface(), CloseLibrary(), ...
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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/27 18:33    #14
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@all :
Thank you for all these precious informations.
When I'll get something to show, I'll post a sample ;)
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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/2/28 21:33    #15
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I encounter another problem with structures.
I've made this with the book help :

struct Basic3DStructType{
  int *LastCreatedObject;
 };
struct Basic3DStructType Basic3D;

struct Object3DType{
  int *PreviousObject, *NextObject;
 };

void BASIC3D_Destructor( void ){
  struct ObjectType *NewObject = Basic3D.LastCreatedObject;
   struct Object3DType *NextToDelete = NewObject.PreviousObject;
 }


I've removed other lines to just show what is wrong ...
I get an error on this line :
Quote:
struct Object3DType *NextToDelete = NewObject.PreviousObject;


BAsic3D.c:64: error: request for member 'PreviousObject' in something not a structure or union

Why ?

I tried to change struc to these :
Quote:
struct Object3DType{
int PreviousObject, NextObject;
};

Same Result ...

Any info ?
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Gazelle
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/3/1 0:06    #16
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@freddix
Quote:
void BASIC3D_Destructor( void ){
  struct ObjectType *NewObject = Basic3D.LastCreatedObject;
  struct Object3DType *NextToDelete = NewObject.PreviousObject;
 }

BAsic3D.c:64: error: request for member 'PreviousObject' in something not a structure or union

Why ?


That's because NewObject is a pointer to a structure and not a structure.

To access elements of a structure through a pointer you need the "->" operator.

struct Object3DType *NextToDelete = NewObject->PreviousObject;


Would be correct but will cause a DSI if NewObject is NULL.

This should work:
struct Object3DType
{
  struct Object3DType *PreviousObject;
  struct Object3DType *NextObject;
  /* rest of the objectdata */
};

struct Basic3DStructType
{
  struct Object3DType *LastCreatedObject;
};
struct Basic3DStructType Basic3D;

void BASIC3D_Destructor( void )
{
  struct Object3DType *NewObject = Basic3D.LastCreatedObject;

  if (NewObject != NULL)
  {
    struct Object3DType *NextToDelete = NewObject->PreviousObject;
    /* your code */
  }
}

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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/3/1 0:26    #17
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@Gazelle
ok.

Now I understand how the pointer in struc works.

Thank you Gazelle.


When compiling, I also get some errors on things I'read here for example :

definition :
typedef struct Object3DType{
 ...
 };


Object3DType *Allocate3DObject( int ObjectID ){
  ...
 }

Basic3D.c:48: error: expeted '=', ',', ';', 'asm' or '__attribute__' before '*' token

and

void Free3DObject( Object3DType *OldObject ){
 ...
 }

Basic3D.c:71: error: expected ')' before '*' token

Why ? I use exactly what was adviced to me here in this post ...

Kindest Regards,
Freddix


Edited by freddix on 2009/3/1 10:55:00
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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/3/1 22:06    #18
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@freddix
no one know ?
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Shadow
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/3/1 22:12    #19
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@freddix


I think this is wrong:

typedef struct Object3DType{
 ...
 };


and should be:

typedef struct {
 ...
 } Object3DType;

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AmiDARK
Re: GCC, Dynamic structure creation method ?
Posted on: 2009/3/1 22:24    #20
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@Shadow
When I make the changes you said, I get several other error ...

Like :
Basic3D.c:56: error: request for member 'PreviousObject' in something not a structure or union

and previous object is a component of the struct defined ...
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