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make_dll and call_external woes [message #70469]

Sun, 18 April 2010 15:02

James[2]
Messages: 44
Registered: November 2009

Member

Hi everyone,

I'm working on some code that's loop-heavy, so I'd like to do the
loopy part with an external C program. I'm using MAKE_DLL to compile
and then CALL_EXTERNAL. My system is Windows XP with the Microsoft
Visual C++ Express compiler, running in 32-bit mode.

I'm using very large data sets, so I would like to pass only pointers
to my C function. I wrote a little test program like this. It takes
all the arguments that my actual program needs, but it just alters one
value to see if anything happens:

void raycast(unsigned char * image, unsigned char * angles, unsigned
char * magnitudes, int * dims)
{
angles[0] = 100;
}

I compile this using MAKE_DLL successfully. I've tested if the code
is getting called by adding an IDL_message(), and it works - the
message prints out on the IDL console. Unfortunately, the above code
does not work. I call it in IDL like this:

[stack is a preexisting 3-dimensional byte array]
dims = fix(size(*stack, /dimensions))
angles = ptr_new(bytarr(dims))
magnitudes = ptr_new(bytarr(dims))
dimsptr = ptr_new(long(reverse(dims)))
call_external (dir + "raycast.dll", "raycast", $
stack, angles, magnitudes, dimsptr, /cdecl, /all_value)

but when I check the value of (*angles)[0] afterward, it's still 0. I
also check with max(*angles) and it's 0 as well. Why is my C program
not changing anything in the array? I get the same problem whether I
include the /ALL_VALUE keyword or not.

Many thanks to anyone who can make sense of this issue!

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[Message index]

		make_dll and call_external woes By: James[2] on Sun, 18 April 2010 15:02
		Re: make_dll and call_external woes By: Craig Markwardt on Sun, 18 April 2010 16:33
		Re: make_dll and call_external woes By: James[2] on Fri, 21 May 2010 09:26
		Re: make_dll By: Wout De Nolf on Wed, 11 May 2011 06:58
		Re: make_dll By: cgoethel on Tue, 10 May 2011 17:26
		Re: make_dll By: Michael Galloy on Tue, 10 May 2011 14:47

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