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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: GISList: Arguments to DLL Call |
| Date: |
08/30/2001 02:13:21 PM |
| From: |
Bill Thoen |
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Santosh Nandi wrote:
> 1.Is there any solution where a structure needs to be passed in a DLL Call.As far as I know Avenue does not support this datatype.
When faced with DLL structures that contain data types not
supported by the calling program, you can always fake them with
data types you can support. For example, suppose you encountered
a structure like so:
...
size as BYTE
name as LPSTR
...
I don't know Avenue, but I bet you can support the LPSTR as a
plain String type. But suppose you didn't have an eight-bit byte
data type to substitute for BYTE. In that case, use a short
integer, like so (using MapBasic types):
...
size as SmallInt
name as String
...
To handle this structure, you need to know that the data that
represents the BYTE goes in the low-order half of 'size', the
first character of the string is in the high-order byte of 'size'
and the rest of the string is in 'name'. To write the value 14
into size and "Arial" into name, you use the following formula
for 'size'.
size = Asc("A") * 256 + 14
and then set name like so:
name = "rial"
Put these in your structure and as far as the DLL is concerned,
all the data elements are in the right place.
To read these values back, you can do it this way:
name = Chr$(sizeŽ) & name
size = size mod 256
Note the integer divide '' as opposed to the normal division
operator '/'. The trick is using integers to take the place of
bytes. When passed between caller and API, they're all just bits
in memory anyway: all you have to do is arrange them in the right
order.
> 2. I want to change my screen resolution through Avenue.What arguments should I pass to the DLL Call "Change Display Settings"
My guess is that you want SetGraphicsMode(). You need to get a
handle to the device context first (GetDC()), and I think you
need to also need to do something with ModifyWorldTransform().
Also don't forget to call ReleaseDC() when you're done. If you
don't have the API Bible by Dan Appleton or something comparable,
then you'll need to search places like http://www.ezvb.com/ for
the details.
--
- Bill Thoen
------------------------------------------------------------
GISnet, 1401 Walnut St., Suite C, Boulder, CO 80302
tel: 303-786-9961, fax: 303-443-4856
mailto:bthoen@gisnet.com, http://www.gisnet.com/
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