From: "Stephan Kämper" <Stephan.Kaemper@...>
Date: 2005-03-29T22:49:48+09:00
Subject: Re: DL usage / DL documentation

Eric Hodel wrote:
> On 28 Mar 2005, at 09:59, Stephan K�mper wrote:
> 
>> Hi all,
>>
>> I currently try to call a function in a DLL, which has a prototype 
>> like this:
>>
>> int test(int an_int, long * a_ptr_to_long, char * a_string);
>>
>> How do I get a 'long *' into the method from Ruby using DL?
> 
> DL just does it:

Thanks for answering. I'm sure it does. But apparently I'm a bit stupid 
these days - I still don't get it. <blush/>

> require "dl"
> require "dl/import"
> require "dl/struct"
> 
> module LIBC
> 
>   extend DL::Importable
> 
>   dlload "libc.dylib"
> 
>   typealias "const time_t *clock", "long ref"

What does the 'clock' and 'ref' part mean it this typealias?
Does that mean a "const time_t *" is just another (type) name for "long"?

>   StructTm = struct [
>     "int tm_sec",     # seconds (0 - 60)
>     "int tm_min",     # minutes (0 - 59)
>     "int tm_hour",    # hours (0 - 23)
>     "int tm_mday",    # day of month (1 - 31)
>     "int tm_mon",     # month of year (0 - 11)
>     "int tm_year",    # year - 1900
>     "int tm_wday",    # day of week (Sunday = 0)
>     "int tm_yday",    # day of year (0 - 365)
>     "int tm_isdst",   # is summer time in effect?
>     "long tm_gmtoff", # offset from UTC in seconds
>     "char *tm_zone",  # abbreviation of timezone name
>   ]
> 
>   extern "struct tm * localtime(const time_t *clock)"
> 
>   def self.c_localtime(clock)
>     tm = LIBC.localtime(clock)
>     return LIBC::StructTm.new(tm)
>   end
> 
> end
> 
> p LIBC.c_localtime(Time.now.to_i).tm_min

What would I have to do if the called DLL function changes the thing 
pointed to?

I'll just return to 'my' function mentioned above:
 > int test(int an_int, long * a_ptr_to_long, char * a_string);

As far as I understood, something like this might be a start:

require "dl"
require "dl/import"
require "dl/struct"

module Foo
     extend DL::Importable
     dlload "mylinb.dll"
     extern "int test(int, long *, char)"
end

# Now create some variables, to pass into 'Foo.test'

index = 42
name  = "F. Prefect"

# ... missing code here to create ptr_to_long

ret = Foo.test( index, ptr_to_long, name )

How (I think) that's my question: How can I creatthat ptr_to_long thing 
- and how would I get back the value (to which it points after the 
function call)?

Still confused (I should incorporate some C/C++ in one of my next 
projects to used to pointers and pointees again...)

Happy rubying

Stephan