[Rd] problem typcasting return of R_ExternalPtrAddr(SEXP s)
Prof Brian Ripley
ripley at stats.ox.ac.uk
Mon Sep 20 18:55:12 CEST 2004
It's a warning, and occurs several times in R itself. I don't think it is
fatal to live with it.
There exists systems on which function pointers are not simple pointers,
but probably none of them run R -- and they do not support dynamic loading
of packages' DLLs if they do.
On Mon, 20 Sep 2004 wsetzer at mindspring.com wrote:
> In the odesolve routine lsoda(), I allow the function (named func) that calculates the system of differential equations to be defined in a dll that has been dynamically loaded from the file named in dllname. I use getNativeSymbolInfo(func, dllname)$address to get the address of the function and pass it to a C function called via the .Call interface. Inside that C function, I use R_ExternalPtrAddr(deriv_func) to get the function pointer. This requires typcasting the return value of R_ExternalPtrAddr from (void *) to (deriv_func *), defined in a typedef in call_lsoda().
> To be more explicit (I'm replacing irrelevant arguments with ellipses):
> In lsoda(...,func,dllname,...), func contains a string giving the name of a function which is defined in the dll whose name is contained in dllname.
> inside lsoda() are lines like
> func <- getNativeSymbolInfo(symbol.C(func),PACKAGE=dllname)
> inside call_lsoda.c are the lines:
> SEXP func;
> typedef void deriv_func(long int *, double *,double *, double *);
> derivs = (deriv_func *) R_ExternalPtrAddr(func);
> This all worked up to now, but now, (as Kurt Hornik kindly informs me) gcc 3.4 gives the warning:
> warning: ISO C forbids conversion of object pointer to function pointer type
> so I need to clean this up so odesolve will compile cleanly for version 2.0.0 of R. I'm at a loss of what to do, though, since the return value of R_ExternalPtrAddr is (void *), and I need a function pointer.
> I'd guess there would need to be a special function (say declared as
> ( R_ExternalFnPtr(SEXP s) *)(),
> or something like that), to make all this work, but I can't find such a function. My C programming is pretty rusty, so I'm wondering if someone has an idea about how I can get around this problem (or perhaps I've misunderstood the meaning of the error message? )
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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