[R] Re: [Rd] programming with C++Builder 5

[Simon Urbanek]

On Dec 31, 2003, at 10:17 AM, Edward Feng wrote:

> I am using C++ Builder 5 to develop windows GUI interface for a R 
> library package.  I have to pass R objects to and from C functions and 
> also evaluate them within C functions.  But I always got linking error 
> message of "unresolved external functions" with those internal 
> functions or macros defined in Rinternals.h file.  I can not find the 
> reason.

There are many possible reasons -  you didn't say anything about how 
you exactly access the DLL, create the R.lib etc. All I can do is to 
imagine what you did wrong, so I hope this will cover some of it.

There are following pitfalls I can think of (I omitted obvious ones 
like include paths and run-time issues like determining R_HOME etc.)

1) You should globally define Win32 in your project - depending on the 
BCC you use this may not be the default, and R relies on it

2) C vs C++:
I assume that you'll be using C++ (otherwise there's no need for C++ 
Builder ;)). R.dll exports are all in C language, most of them are also 
in the C calling convention. You must be aware of this when interfacing 
externals. Note that there are several includes that you need to wrap 
in export "C" { ... }!

If you see symbol "R_xxx" not defined then you have this C vs. C++ 
problem. If something else is wrong you should see symbol "_R_xxx" not 
defined - that's in fact an improvement!

3) R.DEF
BCC and gcc disagree about the notations in the DEF file. I assume that 
you won't use any STDCALL functions of R (it's just some bz2 func 
etc.), so I'll skip that issue.
BCC is looking for the exports of the form _function - so you need to 
modify the R.DEF supplied with R in order to be usable with BCC. You 
need to do two things:
- remove all hints (the @nnn at the end of all lines)
- mangle all function names, i.e. the line:
R_DefParams @215
should become:
_R_DefParams=R_DefParams
This can be easily done by a simple script.

4) generate a R.lib with implib -c R R.def

Now you're ready to use R.dll in your program. But before you plunge 
into writing some Win apps that interface to R, you should definitely 
look at other projects that use R.dll - there is a lot of issues you 
should be aware of, especially involving the initialization of R (Win32 
version has no Rf_initEmbeddedR).

Cheers,
Simon

---
Simon Urbanek
Department of computer oriented statistics and data analysis
Universitätsstr. 14
86135 Augsburg
Germany

Tel: +49-821-598-2236
Fax: +49-821-598-2280

Simon.Urbanek at Math.Uni-Augsburg.de
http://simon.urbanek.info