[Rcpp-devel] Missing PROTECT()s in forward_exception_to_r()?

[North, Ben]

Hi Dirk, Douglas,

Many thanks for your time in digging into this.  I did some further
experiments yesterday and cut down the PROTECT()s a bit, but your
version below is much tidier.  I confirm that your suggested code

        SEXP cppExceptExpr = PROTECT(Rf_lang3(cppExceptSym,
                                              Rf_mkString(exception_what.c_str()),
                                              Rf_mkString(exception_class.c_str())));
        Rf_eval(cppExceptExpr, R_FindNamespace(Rf_mkString("Rcpp"))); // Should not return.

        // Do this in case somehow someone replaces the definition of
        // "cpp_exception" such that it does return:
        UNPROTECT(1);

behaves correctly in my case.  For completeness, the full text of the
forward_exception_to_r() function I now have is:


void forward_exception_to_r( const std::exception& ex){
    std::string exception_class ;
    std::string exception_what  = ex.what();
    const char *name = typeid(ex).name() ;
    // now we need to demangle "name"
    {
        int status = -1;
        char *dem = 0;
        dem = abi::__cxa_demangle(name, 0, 0, &status);
        if( status == 0){
            exception_class = dem ; /* great we can use the demangled name */
            free(dem);
        } else{
            exception_class = name ; /* just using the mangled name */
        }
    }
    SEXP cppExceptSym = Rf_install("cpp_exception"); // cannot cause a gc() once in symbol table
    SEXP cppExceptExpr = PROTECT(Rf_lang3(cppExceptSym,
                                          Rf_mkString(exception_what.c_str()),
                                          Rf_mkString(exception_class.c_str())));
    Rf_eval(cppExceptExpr, R_FindNamespace(Rf_mkString("Rcpp"))); // Should not return.

    // Do this in case somehow someone replaces the definition of
    // "cpp_exception" such that it does return:
    UNPROTECT(1);
}


(I did try using Rf_install() but as Douglas predicted, this creates a
symbol rather than a string, and cpp_exception doesn't like this.)

I am now seeing another strange error under gctorture() which I might try
to track down further, and will report back if it looks like Rcpp rather
than my code.

Thanks,

Ben.


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