[R] Neophyte question re using dyn.load and accessing c functions

[Prof Brian D Ripley]

On Sun, 25 Apr 1999, Robert Gentleman wrote:

> 
> 
> On Sun, 25 Apr 1999, Barnet Wagman wrote:
> 
> > I'm have what's probably a trivial &| silly problem trying to access a
> > c-function in a shared
> > library ( R 0.64, under redhat linux 5.2).
> > 
> >     R COMPILE rctest.c
> >     R SHLIB -o libRC.so rctest.o
> > 
> > produce a reasonable looking shared library ('nm libRC.so' shows that
> > the function 'rctest' is present).
> > 
> > In R, the command
> > 
> >     dyn.load("/fullpathname/libRC.so")
> > 
> > returns without an error.  However, I'm unable to access the function.

Just to point out that tests almost nothing (at present). You can have
a library that loads with unresolvable symbols that will throw you out of
R when you try to use the symbol.  About the only think it tests is the
presence of the library file.

> > E.g.
> > 
> >     is.loaded(symbol.C("rctest"))
> > 
> > yields FALSE.
> > 
> >     .C("rctest",x)
> > 
> > yields "Error in .C("rctest", x) : C/Fortran function not in load table"
> > 
> Well when this happens to me it's usually because R configured incorrectly
> and decided to either prepend (or not) an underscore when it wasn't (or
> was) needed. 
> Stepping through the code using a symbolic debugger will let you know
> what's going on (or you could try recompiling with
> HAVE_NO_SYMBOL_UNDERSCORE, set to the correct value for your machine).

You can test if the configuration is right by

library(mva)
example(cmdscale)

If that fails it is the system configuration: if it works it is your
example, about which we will need to know more to help....

(This is such a common system for R it is hard to imagine that
configure did not work, but there is always a first time.)

-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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