[Rd] calling fortran from C

[Peter Dalgaard]

"James Bullard" <bullard at berkeley.edu> writes:

> Hello, I had a question about calling some of R's fortran routines from C.  
> Specifically, I would like to call: dqrfit from some C code which will be  
> bundled as an R package. I was hoping someone knew of an example in some  
> of R's code which does something like this (any fortran call from R's C  
> would probably be a sufficient guide). So far I can only find locations  
> where R calls the Fortran directly, but this is not an option for me.
> 
> Also, I am trying to gauge the overhead of making this call, does anyone  
> have any knowledge of whether there might be some non-trivial constant  
> time penalty on making such a call.
> 
> Thanks in advance, Jim

The penalty is no bigger than on ordinary C calls. The main issue is
to get the naming convention right (HAVE_F77_UNDERSCORE, etc) and call
dqrfit_(....) if required -- all in a portable way. 

The whole thing is described in the Writing R Extensions manual,
section 5.6 specifically.



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