From: Eric Hodel <drbrain@...7.net>
Date: 2005-03-30T04:04:22+09:00
Subject: Re: DL usage / DL documentation


On 29 Mar 2005, at 05:49, Stephan K�mper wrote:

> 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
>

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
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