Re: gcc linking and address of template function

[Perry Smith <pedz@easesoftware.com>]

I may be right in front of my face but I don't see it.  Can you send  
a couple lines of what the link's error messages are like?

On May 5, 2006, at 4:29 PM, Brian Budge wrote:

> Hi all -
>
> I'm attempting to use gsl (gnu scientific library) from my C++
> program.  gsl is a C program, and I need to pass function pointers to
> gsl to make it do it's magic on my data.
>
> The problem I'm having stems from the fact that I need my functions to
> be template functions.
>
> I can get everything to compile, but I can't get it to link.
>
> The gist is like this:
>
> template<class Stencil>
> int ll_uv_f(const gsl_vector *x, void *params, gsl_vector *f){
>    LL_uv_data<Stencil> *lld = static_cast< LL_uv_data<Stencil>* > 
> (params);
>    const real a = gsl_vector_get(x,0);
>    const real b = gsl_vector_get(x,1);
>    Vec v = lld->ll->eval(a, b) - lld->pt;
>    for(int i = 0; i < 2; ++i){
>        gsl_vector_set(f, i, v[i]);
>    }
>    return GSL_SUCCESS;
> }
>
> template<class Stencil>
> int ll_uv_df(const gsl_vector *x, void *params, gsl_matrix *J){...}
>
> template<class Stencil>
> int ll_uv_fdf(const gsl_vector *x, void *params, gsl_vector *f,
> gsl_matrix *J){...}
>
> The calling function then contains the code:
>
> LL_uv_data<BaseStencil> dat(Vec(u,v), this);
> gsl_multiroot_function_fdf f = {ll_uv_f<BaseStencil>,
>                                           ll_uv_df<BaseStencil>,
>                                           ll_uv_fdf<BaseStencil>,
>                                           2, &dat};
>
> I also explicitly instantiate the template functions for several
> instances in a .cc file:
>
> //explicit instantiation of template functions
> template int ll_uv_fdf<CCStencil>(const gsl_vector *x, void *params,
> gsl_vector *f, gsl_matrix *J);
> template int ll_uv_fdf<BSStencil>(const gsl_vector *x, void *params,
> gsl_vector *f, gsl_matrix *J);
> .
> .
> .
> template int ll_uv_df<CCStencil>(const gsl_vector *x, void *params,
> gsl_matrix *J);
> template int ll_uv_df<BSStencil>(const gsl_vector *x, void *params,
> gsl_matrix *J);
> .
> .
> .
> template int ll_uv_f<CCStencil>(const gsl_vector *x, void *params,
> gsl_vector *f);
> template int ll_uv_f<BSStencil>(const gsl_vector *x, void *params,
> gsl_vector *f);
> .
> .
> .
>
> The program compiles fine, and the functions int ll_uv_*() are found
> by the nm utility to be in a .o file.
>
> The program still won't link.  Anyone have any ideas?  Is this
> something I'm doing wrong?  The gcc version is 3.4.5-r1, and this is
> on a xeon box running linux.
>
> Thanks,
>  Brian
>