| Re: Returning pointers from C DLL [message #12594] |
Tue, 25 August 1998 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Simon Hall (shall@atm.ch.cam.ac.uk) writes:
> I need to write a dll that returns a pointer to an array of strings, ie
> I want to return a char** type.
>
> I can get it to return a single string using the /s_value keyword to
> call_external. How do I return an array of strings? I can't see any
> option to return a pointer.
I think you are misunderstanding how things get back
from Call_External. You want to pass the string array
as an *argument* to Call_External. It is better to think
of the return value of Call_External as a value that tells
you whether the function call was successful or not.
myStringArray = StrArr(10)
ok = Call_External('my.dll', 'fill_string', myStringArray)
Cheers,
David
----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Returning pointers from C DLL [message #12599 is a reply to message #12594] |
Tue, 25 August 1998 00:00  |
rivers
Messages: 228
Registered: March 1991
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Senior Member |
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In article <35E2B4EB.E2C2577F@atm.ch.cam.ac.uk>, Simon Hall <shall@atm.ch.cam.ac.uk> writes:
> Hi,
>
> I need to write a dll that returns a pointer to an array of strings, ie
> I want to return a char** type.
>
> I can get it to return a single string using the /s_value keyword to
> call_external. How do I return an array of strings? I can't see any
> option to return a pointer.
I don't think that IDL would know what do with a char** type. IDL stores
and passes strings by descriptor. However, if what you want to do is to return
an array of strings, there is a workaround which I have used. Return instead a
2-D byte array, where each row of the byte array is one string. You can then
just use the IDL STRING() function to convert the byte array to a string array.
You cannot return this array as the function value, you will have to pass it as
a parameter to the function, where you dimension and create the array in IDL
before calling your function. If you can't live with these limitations then
you will have to use LINKIMAGE.
Here is an example from one of my programs:
array = bytarr(40, 16)
n = 0L
status = call_external('ezca', 'ezcaIDLGetEnumStrings', n, array)
if (status ne 0) then return, status
strings = string(array(*, 0:n-1))
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