Re: error loading cxx local model in isis: undefined symbol

Hi John,

I am also confused by the need to declare a function which is explicitly 
named "c_test". A few years ago when I wrote a wrapper function to make 
a C interface for a C++ style XSPEC model, this wasn't the case - if I 
had written a C style XSPEC model called "test", then it would work with 
no further modification in isis. Did you change the way isis interfaces 
with XSPEC local models?

Maurice

On 11/19/13 11:06 AM, Thomas Dauser wrote:
> Hi John,
>
> thanks for your reply. Still, I'm confused. I'm trying to understand 
> why local models in C are so much more complicated for isis than in 
> xspec.
>
> I got the C++ model running, exactly as you described. Is there a 
> reason why one has to write a wrapper for isis, which is done by xspec 
> automatically. But not the way I understood it from Maurice, although 
> this approach made much more sense in my opinion. Now I have to define 
> a C++ model with
>
> extern "C" test void( ... )
>
> and a wrapper converting this to C with
>
> extern "C" C_test void( ... )
>
> Note the C_test. Any other function name else won't work. Why do I 
> have to create a wrapper manually in isis, while xspec automatically 
> does it perfectly fine?
>
>
> While I more or less understand the issue with C++ above, I'm totally 
> confused with the C case (so, from here on, I'm only talking about a C 
> model). Following the heasoft guide for local models 
> (http://heasarc.gsfc.nasa.gov/xanadu/xspec/manual/XSappendixLocal.html), 
> it should be possible to just define a local model in C, when 
> referring to it in the lmodel.dat with "c_test" (not the small "c"). . 
> This is basically the test case described in my previous email. There 
> I simply create a C function called
>
> extern "C" test void( ... )
>
> (following the manual). This, again, works nicely in xspec, but isis 
> complains that the function "c_test" is not defined. If I provide this 
> function (simply a C-Wrapper for the C-Function), it works. Why do I 
> have to provide two identical functions with different names for one 
> actual model? (using C_test or c_test as function name also fails. 
> Then isis is looking for a function called "test", which clearly does 
> not exist)
>
>
> Please tell me, if I'm completely missing something or just completely 
> underestimate the complexity of importing local xspec models into 
> isis. Thanks!
>
>
> Cheers,
> Thomas
>
> On 11/19/2013 05:44 AM, John Houck wrote:
>> I think it's just a matter of providing an additional
>> subroutine for a C interface.
>>
>> For example, have a look at how xspec provides C and Fortran
>> interfaces for the xspec internal models. See, e.g.
>>   heasoft-6.14/Xspec/src/XSFunctions/funcWrappers.cxx
>>
>> For a C++ local model that provides a symbol 'test':
>>
>>     extern "C"
>>     void test(const RealArray& energy,
>>               const RealArray& parameter,
>>               int spectrum,
>>               RealArray& flux,
>>               RealArray& fluxError,
>>               const string& init)
>>
>> the lmodel.dat file should, by convention, refer to subroutine
>> C_test.
>>
>> The notation "C_test" means that a C++ interface is provided
>> through the symbol "test", while a C interface (if it exists)
>> should appear under the name "C_test".
>>
>> Following the examples in funcWrappers.cxx, a C-linkage symbol
>> C_test can be defined as in the appended code segment.
>>
>> Once this C-linkage symbol is provided, libxspeclocal.so will
>> contain two symbols through which the local model can be
>> evaluated. C++ programs can call 'test' and C programs can call
>> 'C_test'.
>>
>> If you also want to provide a Fortran linkage symbol, then
>> funcWrappers.cxx shows one way to do that via cfortran.h. One
>> could also use the iso_c_binding module with "modern" Fortran.
>>
>> Thanks,
>> -John
>>
>> // Here's an example C-linkage wrapper definition for 'test'.
>> // An implementation of cppModelWrapper is in funcWrappers.cxx
>> // mentioned above.
>>
>> extern "C"
>> void C_test (const double* energy, int nFlux, const double* params,
>>            int spectrumNumber, double* flux, double* fluxError, const 
>> char* initStr)
>> {
>>     const size_t nPar = 3;
>>     cppModelWrapper(energy, nFlux, params, spectrumNumber, flux, 
>> fluxError,
>>                     initStr, nPar, test);
>> }
>>
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