R help - Jan 2012 - Calling Windows DLL using .C; function name not known but in exports.

First time ever that I try to call subroutines in a Win DLL using R. 
Have done this before using VBA and Python.

The C code's function argument list contains only double pointers 
(double *x). The function is declared void, the output value is one of 
the arguments.
C calling sequence is used.

When inspecting the exports of the DLL with dumpbin I can see that the 
function I need is exported under the name 'planckwR'.

Loading the DLL with dyn.load(dllpath). Works fine. getLoadedDLLs() 
shows info on the 'Planck.dll' that I made. So far so good.

Made a function i R like this:

Planckw<-function(Temp) {
     wavelength<-0.0
     .C('planckwR',as.double(Temp),as.double(wavelength))
     return(wavelength)
}

Calling this function, R complains the function 'planckwR' is not in the
DLL.

This baffled me as I can see it in the exports table using dumpbin.

I use Visual C++ 97 compiler. Old but works. It does change the FPU 
control word, which I know it should not. Working on that one too. Any tips?

Any help much appreciated.
Alex van der Spek

On 12-01-20 10:05 AM, Alex van der Spek wrote:
> First time ever that I try to call subroutines in a Win DLL using R.
> Have done this before using VBA and Python.
>
> The C code's function argument list contains only double pointers
> (double *x). The function is declared void, the output value is one of
> the arguments.
> C calling sequence is used.
>
> When inspecting the exports of the DLL with dumpbin I can see that the
> function I need is exported under the name 'planckwR'.
>
> Loading the DLL with dyn.load(dllpath). Works fine. getLoadedDLLs()
> shows info on the 'Planck.dll' that I made. So far so good.
>
> Made a function i R like this:
>
> Planckw<-function(Temp) {
>       wavelength<-0.0
>       .C('planckwR',as.double(Temp),as.double(wavelength))
>       return(wavelength)
> }
That will return 0.0 once you get the name sorted out; .C won't modify 
the variable wavelength, it will return new values in a list.
>
> Calling this function, R complains the function 'planckwR' is not
in the
> DLL.
I would look in the export table printed by objdump -x to check this.  I 
don't know the dumpbin utility.
>
> This baffled me as I can see it in the exports table using dumpbin.
>
> I use Visual C++ 97 compiler. Old but works. It does change the FPU
> control word, which I know it should not. Working on that one too. Any
tips?
Use gcc?

Duncan Murdoch
>
> Any help much appreciated.
> Alex van der Spek
>
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