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Re: Passing Structures with Pointers with Call_External [message #40461 is a reply to message #40459]

Wed, 11 August 2004 05:40

Bob[2]
Messages: 5
Registered: June 2004

Junior Member

Peter, you might try changing the C-side to accept a struct of many
Planes, then use call_external with a single argument (the name of the
struct) and set /autoglue. E.g.,

function MakePlanes, numrows, numcolumns, sNumberOfPlanes
; put it together. Must be named FloatPlane_Struct.
return,a_planes_struct
end

On the C-side,

typedef struct FloatPlane_Struct
{
/* as before
}

IDL_INT work( struct FloatPlane_Struct *a )
{
; Do your work with a->Rows[j] and so on
; then return to IDL.

return,0;
}

And from the IDL-side again, e.g.

my_planes = MakePlanes(33,12,5)

work_result = call_external('SharedLibrary.so','work',my_planes, $
/AUTO_GLUE,/I_VALUE)

Now, as I have set up my example, 'work' does computations on the
structure 'my_planes' and maybe changes values in it etc., then returns
an IDL_INT when finished. You can make the return type of 'work' to be
something else, like a struct, and instead of /I_VALUE you set
RETURN_TYPE=8.

Have fun working with it.

I am not sure why your other stuff is crashing idlde, though.

> I declare an array of structures thus.
> function MakeFloatPlane,numrows,numcolumns
> temp={Rows:long(numrows),Columns:long(numcolumns),Data:fltar r(numrows,numcolumns)}
> return,temp
> end
>
> Planes=replicate(MakeFloatPlane(nY1,nX1),sNumberOfPlanes)
>
> I then pass the array to C code through Call_External thus.
> Result=Call_External('SharedLibrary.so','CFunction_cw',sNumb erOfPlanes,Planes,/unload)
>
> The C code is as follows.
> typedef struct FloatPlane_Struct
> {
> long Rows;
> long Columns;
> float **Data;
> } FloatPlane;
>
> extern "C" long CFunction_cw(int argc, void *argv[])
> {
> long lNumberOfPlanes;
> FloatPlane *fppPlanes;
> float *fpData;
>
> lNumberOfPlanes=*((long *)(argv[0]));
> fppPlanes=((FloatPlane *)(argv[1]));

> However, I cannot interpret the result I get for fppPlanes->Data.
>
> If I add
> fprintf(stderr, "fppPlanes->Data[0]=%d\n", fppPlanes->Data[0]);
> idlde crashes, presumably due to a memory write error in the C code.
> Is there any way to stop idlde crashing under such circumstances?
>
> My main question is this. Is there a way to retrieve the IDL variable
> Planes[i].Data within CFunction_cw?

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[Message index]

		Re: Passing Structures with Pointers with Call_External By: MajorSetback on Wed, 11 August 2004 07:34
		Re: Passing Structures with Pointers with Call_External By: MajorSetback on Wed, 11 August 2004 06:53
		Re: Passing Structures with Pointers with Call_External By: MajorSetback on Wed, 11 August 2004 06:53
		Re: Passing Structures with Pointers with Call_External By: Bob[2] on Wed, 11 August 2004 05:40
		Re: Passing Structures with Pointers with Call_External By: Peter Mason on Tue, 10 August 2004 16:12
		Re: Passing Structures with Pointers with Call_External By: Peter Mason on Wed, 11 August 2004 16:44

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