From: ptkwt@... (Phil Tomson)
Date: 2005-11-05T09:22:09+09:00
Subject: Re: In an extension, doing a Data_Make_Struct and getting value back

In article <B7Raf.6263$Kv.5852@newssvr22.news.prodigy.net>,
JSW <jsw@abc.com> wrote:
>A snippet  of the code around the Get and Make parts:
>....
>    SQLHANDLE hDb;
>    VALUE retVal;
>    handle  hCon;
>    VALUE conRet;
>    sConnect *sC;
>
>    conRet = Data_Make_Struct(cDB2Conn, sConnect, 0, free, sC);
>    sC->connection = hDb;
>    return conRet;
>
>and the later part where it's used:
>
>    handle *hCon;
>    Data_Get_Struct( conHandle, handle, hCon );

(What type is conHandle?  It should be a VALUE holding a Class)
OK, so you the 'c-type' you gave to Data_Make_Struct was sConnect, but 
you're asking for something with a type of handle back, wouldn't you want:

     sConnect *hCon;
     Data_Get_Struct( conHandle, sConnect, hCon); 

instead?

>
>This is where it fails with "incorrect class - Data expected"

Well, I didn't use Data_Make_Struct, but here's an example from my code 
using Data_Wrap_Struct, maybe it'll help:

/*begin point.c code*/
typedef struct {
        double x;
        double y;
        double z;
} ACO_3DPoint_Struct;

//allocator
static VALUE aco_point_alloc(VALUE klass) {
  VALUE object;
  ACO_3DPoint_Struct* point = (ACO_3DPoint_Struct*)malloc(sizeof( 
ACO_3DPoint_Struct));
  object = Data_Wrap_Struct(klass,0,aco_point_free,point);
  return object;
}

//initialize
static VALUE aco_point_init(VALUE self, VALUE x, VALUE y, VALUE z){
  ACO_3DPoint_Struct* _self ;
  //double x, y;
  Data_Get_Struct(self, ACO_3DPoint_Struct, _self);
  _self->x = NUM2DBL(x);
  _self->y = NUM2DBL(y);
  _self->z = NUM2DBL(z);
  return self;
}

static VALUE aco_point_getx(VALUE self){
  ACO_3DPoint_Struct *_self;
  Data_Get_Struct(self, ACO_3DPoint_Struct, _self);
  return rb_float_new(_self->x);
}

static VALUE aco_point_setx(VALUE self, VALUE x){
  ACO_3DPoint_Struct* _self;
  Data_Get_Struct(self, ACO_3DPoint_Struct, _self);
  _self->x = NUM2DBL(x);
}
//skip a lot of stuff...

VALUE cACOMod;
VALUE cACOPoint3D;


void Init_aco_point3d() {
  printf("ACO_Ext initializing...\n");
  cACOMod = rb_define_module("ACO");

  cACOPoint3D = rb_define_class_under(cACOMod,"Point3D",rb_cObject);
  //cACOPoint3D = rb_define_class_under(cACOMod,"Point3D",rb_cObject);
  cACOGraph = rb_define_class_under(cACOMod,"Graph",rb_cObject);
  rb_define_alloc_func(cACOPoint3D, aco_point_alloc);
  rb_define_method(cACOPoint3D,"initialize",aco_point_init,3);
  //skip a lot of operators
}
/*end point.c */

Phil