[R] STRING_PTR_RO compared to STRING_ELT

[Iris Simmons]

STRING_PTR_RO(x)[i] will not check bounds and will not check that the
element is not NULL and not a free node. STRING_PTR_RO only works on
standard vectors, and will not work on alternate vector representations.
Also, it will return (const SEXP *) (void *) 1 when the character vector is
of length 0, or may return a pointer to a random place in memory. In
general, I would suggest

const SEXP *y = NULL;
if (Rf_xlength(x)) y = STRING_PTR_RO(x);

or something similar in order to avoid anything weird involving 0 length
access.

I do not know of any other differences to note.

On Mon, Oct 5, 2026, 11:36 Tim Taylor <tim.taylor using hiddenelephants.co.uk>
wrote:

> Apart from different ergonomics is there anything worth being aware of
> when using STRING_PTR_RO versus STRING_ELT for getting CHARSXP?
>
> Tim
>
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