| Re: dlm returning ptr array and string array [message #34352 is a reply to message #34280] |
Tue, 04 March 2003 03:03   |
Nigel Wade
Messages: 286
Registered: March 1998
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Senior Member |
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Reimar Bauer wrote:
> Randall Skelton wrote:
>> On Mon, 3 Mar 2003, Reimar Bauer wrote:
>>
>>
>>>> >Now my questions:
>>>> >Is it possible to return a pointer vector by a dlm?
>>>>
>>>> I am not entirely sure I understand what you are asking here. You
>>>> cannot create an IDL pointer in C, so if that is what you are asking
>>>> you'll need
>>>> to rethink things. You can, create and return IDL variables and arrays
>>>> of
>>>> any type (other than pointers). Likewise with structures but you cannot
>>>> directly interface these as objects (unless, of course, Ronn has some
>>>> new tricks to show us)
>>>
>>> I found an article from Nigel Wade by searching google so I think it is
>>> possible or ?
>>> .http://groups.google.de/groups?hl=de&lr=&ie=UTF-8&a mp;threadm=aoehm9%247pf6%241%40rook.le.ac.uk&rnum=9& prev=/groups%3Fq%3Ddlm%2B%252Bpointer%26hl%3Dde%26lr%3D%26ie %3DUTF-8%26selm%3Daoehm9%25247pf6%25241%2540rook.le.ac.uk%26 rnum%3D9
>>
>>
>> Yes, if all you want to do is return a C pointer, then what Nigel
>> suggests
>> is absolutely fine. In my dlms for postgresql rather than return the
>> pointer directly cast as a long, I build a table of simple connection or
>> result indicies that keeps track of the C pointers. In this way, I can
>> return a simple index number rather that I can subsequently use to
>> 'lookup' the pointers in C (much like the IDL/Fortran LUNs work). I did
>> this after a few people using my code commented that the bizarre unsigned
>> long integers that represented my C pointers must signify an error has
>> occurred. What you cannot do is directly create an IDL pointer in C
>> (i.e. IDL> a = ptr_new(...)).
>>
>> If you are going to write your own data format, you may want to use the
>> XDF or CDF network formats as these are cross-platform for posix
>> machines.
>>
>
> Dear Randall,
>
> thanks again.
>
> I am not thinking about writing one more own format. We all have enough
> done already. Since 1996 we are using netCDF and I don't like changing
> this. We are using for attributes which might be necessary and parameter
> names a definition in our institutes. This means wrong typed attributes
> are ignored by reading and writing. But the sources must be only once
> written and doesn't need cases for different written attributes.
> 'pi_organisation','pio' of everyone.
>
> So we have designed in 1998 a data definition structure for exchanging
> data between netCDF files and IDL. This structure is able to load every
> kind of data from every kind of data format. We have a lot of experience
> of this. In the last years this structure got's more and more important
> for us because several people wrote routines for example to make a time
> synchronisation, read/write different dataformats, different plot
> routines, statistical routines etc.
>
> Here is a routine to create a template of the data structure I am
> speaking from
>
> wget
>
http://www.fz-juelich.de/icg/icg-i/idl_icglib/idl_source/idl _html/dbase/download/write_icgspro.sav
>
> or
>
> wget
>
http://www.fz-juelich.de/icg/icg-i/idl_icglib/idl_source/idl _html/dbase/download/write_icgspro.tar.gz
>
>
> write_icgspro,'test.pro',/small,short=['time','O3']
>
>
> So now back to dlm. I will try to find a way to get independent from the
> used netCDF lib by rsinc for our reading routine. Later netCDF versions
> for example did not need to copy first the file if you add some new
> data. And if neccesary I can use a patch.
>
> I have again a question about the pointer I got back from the dlm.
> Can I use it in idl, print,*ptr or is it only useable from an other c
> call.
>
Unfortunately, it's only useable within code which can utilize raw memory
addresses; it's a C pointer, which is in essence a memory address.
Can you use the same code you currently use to build the vector of IDL
pointers from the structures returned by a DLM?
--
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555
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