Creating an IDL array within C?

Hi guys,

Another problem for everyone. Yay!

Firstly, I'm working on translating code from IDL to C for CUDA
purposes by re-writing it as a system routine.

so the issue:

Within IDL, the user can do this

IDL> help, data6
DATA6 UNDEFINED = <Undefined>

and call an arbitrary function that will have it created.

thisfunc, data6, wv

Within thisfunc.pro
pro thisfunc, data6, wv
data6 = fltarr(5,6)

How do I do this in C?
Is it even possible or do I have to ensure that data6 exists before I
call my system routine?

Regards
Zaki

On Aug 30, 1:40*am, "hotplainr...@gmail.com" <hotplainr...@gmail.com>
wrote:
> Hi guys,
>
> Another problem for everyone. Yay!
>
> Firstly, I'm working on translating code from IDL to C for CUDA
> purposes by re-writing it as a system routine.
>
> so the issue:
>
> Within IDL, the user can do this
>
> IDL> help, data6
> DATA6 * * * * * UNDEFINED = <Undefined>
>
> and call an arbitrary function that will have it created.
>
> thisfunc, data6, wv
>
> Within thisfunc.pro
> pro thisfunc, data6, wv
> * *data6 = fltarr(5,6)
>
> How do I do this in C?
> Is it even possible or do I have to ensure that data6 exists before I
> call my system routine?
>
> Regards
> Zaki

When you create the function prototype you declare the variable, even
if it has no value at that time.
In your case 'data6' could be a pointer variable for an as yet unsized
or variable sized array
-at least that's how I remember ANSI C should work e.g.

<myheader.h>

int thisfunc(float *data6, int wv ....);

Cheers

On Aug 30, 10:52*am, MC <Morefl...@gmail.com> wrote:
> On Aug 30, 1:40*am, "hotplainr...@gmail.com" <hotplainr...@gmail.com>
> wrote:
>
>
>
> > Hi guys,
>
> > Another problem for everyone. Yay!
>
> > Firstly, I'm working on translating code from IDL to C for CUDA
> > purposes by re-writing it as a system routine.
>
> > so the issue:
>
> > Within IDL, the user can do this
>
> > IDL> help, data6
> > DATA6 * * * * * UNDEFINED = <Undefined>
>
> > and call an arbitrary function that will have it created.
>
> > thisfunc, data6, wv
>
> > Within thisfunc.pro
> > pro thisfunc, data6, wv
> > * *data6 = fltarr(5,6)
>
> > How do I do this in C?
> > Is it even possible or do I have to ensure that data6 exists before I
> > call my system routine?
>
> > Regards
> > Zaki
>
> When you create the function prototype you declare the variable, even
> if it has no value at that time.
> In your case 'data6' could be a pointer variable for an as yet unsized
> or variable sized array
> -at least that's how I remember ANSI C should work e.g.
>
> <myheader.h>
>
> int thisfunc(float *data6, int wv ....);
>
> Cheers

No, that's not even close. The OP is asking how to create an IDL
array in a C routine.

It is a lot easier to allocate the array in IDL and pass it to the C
function if you can. But sometimes you don't know the size of the
array until after you are actually in the C code.

Here is the general idea:

Suppose you want to return an IDL variable containing an array [5,6]
of floats. (The dimensions COULD be determined at run time.)
The variable is to be passed to the caller in argv[0].

IDL_MEMINT dim[2];
IDL_VPTR vpVar;
dim[0] = 5;
dim[1] = 6;
float *fp;
fp = (float*) IDL_MakeTempArray(IDL_TYP_FLOAT, 2, dim,
IDL_ARR_INI_NOP, &vpVar);

/* code to fill in array pointed to by fp */

if (argc >= 1)
IDL_VarCopy(vpVar, argv[0]);


See the IDL External Programming Guide for more info.