R devel - Jan 2008 - do_gsub (PR#10540)

In character.c within R 2.6.1, the function do_gsub contains the following 
code:

1199        if (STRING_ELT(pat, 0) == NA_STRING) {
1200            PROTECT(ans = allocVector(STRSXP, n));
1201            for(i = 0; i < n; i++)  SET_STRING_ELT(ans, i, NA_STRING);
1202            UNPROTECT(1);
1203            return ans;
1204        }
1205
1206        if (length(pat) < 1 || length(rep) < 1) error(R_MSG_IA);

Line 1206 checks that pat contains at least one element.  However, line 1199 
has already attempted to access the first element.  The check should surely 
come first.

Andrew Runnalls

I believe STRING_ELT() works even when pat is R_NilValue, so
the first line "does the right thing" even if the first element does
not
exist. I think this is intentional and not a bug.

Other more knowledgeable people please correct me if I am wrong.

A.R.Runnalls at kent.ac.uk wrote:
> In character.c within R 2.6.1, the function do_gsub contains the following 
> code:
> 
> 1199        if (STRING_ELT(pat, 0) == NA_STRING) {
> 1200            PROTECT(ans = allocVector(STRSXP, n));
> 1201            for(i = 0; i < n; i++)  SET_STRING_ELT(ans, i,
NA_STRING);
> 1202            UNPROTECT(1);
> 1203            return ans;
> 1204        }
> 1205
> 1206        if (length(pat) < 1 || length(rep) < 1) error(R_MSG_IA);
> 
> Line 1206 checks that pat contains at least one element.  However, line
1199
> has already attempted to access the first element.  The check should surely
> come first.
> 
> Andrew Runnalls
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel