From: Takaaki Tateishi <ttate@...>
Date: 2002-11-26T20:11:18+09:00
Subject: Re: DL and arrays of pointers

At Tue, 26 Nov 2002 17:55:46 +0900,
> > typedef _foo {
> > 	char * bar;
> > 	unsigned int qux;
> > } Foo;
> >
> > Foo ** foos;
> 
> I tried to define foos = struct[ "Food ** foos" ] but i'm not able to
> access foos[0] at a later time.

"struct[...]" creates something like a wrapper class for struct Foo.
The following example shows how to access foos[0], foos[1],...

--- test.c ---
#include <stdio.h>
#include <stdlib.h>

typedef struct {
  char bar[10];
  unsigned int qux;
} Foo;

/* create_foos() creates Foos */
Foo **create_foos(int n){
  Foo **foos;
  int i;

  foos = (Foo**)malloc(sizeof(Foo*) * n);
  for( i=0; i<n; i++ ){
    foos[i] = (Foo*)malloc(sizeof(Foo));
    sprintf(foos[i]->bar,"%d",i);
    foos[i]->qux = i;
  }

  return foos;
}


-- test.rb --
require 'dl/import'
require 'dl/struct'

module Foo
  extend DL::Importable

  dlload 'test.so'

  typealias "Foo", "void*"

  extern "Foo **create_foos(int)"

  Foo = struct [
    "char bar[10]",
    "int qux",
  ]
end

n = 10
foos = Foo::create_foos(n)
ptr  = foos                          # "ptr = (void*)(foos)" in C layer
for i in 0..(n-1)
  foo = ptr.ptr                      # "foo = *ptr" in C layer
  foo = Foo::Foo.new(foo)            # wrap the pointer
  p [foo.bar.collect{|c| c.chr}.join, foo.qux]
  ptr += DL.sizeof("P")              # increment the pointer
end
-- 
Takaaki Tateishi <ttate@kt.jaist.ac.jp>