[Rd] problem typcasting return of R_ExternalPtrAddr(SEXP s)

From: <wsetzer_at_mindspring.com>
Date: Tue 21 Sep 2004 - 02:10:15 EST

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? )

Woody Setzer

R-devel@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel Received on Tue Sep 21 02:14:31 2004

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