[Rcpp-devel] idiom for creating an informative message for an exception

[Dirk Eddelbuettel]

On 2 December 2010 at 22:46, Romain Francois wrote:
| Le 02/12/10 22:15, Douglas Bates a écrit :
| > In the lme4a package I mixed calls to Rf_error and throwing C++
| > exceptions.  This is causing problems and I plan to replace the calls
| > to Rf_error by exceptions so that there is a consistent approach.
| >
| > Many of the calls to Rf_error take advantage of the fact the Rf_error
| > implicitly calls sprintf to create the error message.  Thus I have
| > calls like
| >
| > 	if (!d_x.size() == d_nrow * d_ncol)
| > 	    ::Rf_error("%s: Dim = (%d, %d) is inconsistent with x.size() = %d",
| > 		       "ddenseMatrix::ddenseMatrix", d_nrow, d_ncol, d_x.size());
| >
| > Is there a similar idiom for creating an exception's "what" argument?
| > I imagine I could add std::strings and maybe use some iostreams or
| > something like that ...
| 
| Maybe you can use sprintf, e.g :
| 
| 
| require( inline )
| require( Rcpp )
| 
| fx <- cxxfunction( , '
| 
|      // replace 100 by whatever is large enough
|      // the backslashes below are just because of R escaping
|      std::string message( 100, \' \' ) ;
|      sprintf( const_cast<char*>(message.data()), "%s %d", "bla bla", 2 ) ;
|      return wrap( message ) ;
| 
| ', plugin = "Rcpp" )
| 
| 
| you could for example use sprintf in the body of the constructor of your 
| exception class.

The problem is very similar to what logging classes do.  Maybe time to
revisit our old and simple macros and do something better?

Dirk

-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com