[Rd] strtoi output of empty string inconsistent across platforms

[Martin Maechler]

>>>>> Michael Chirico 
>>>>>     on Fri, 11 Jan 2019 14:36:17 +0800 writes:

    > Identified as root cause of a bug in data.table:
    > https://github.com/Rdatatable/data.table/issues/3267

    > On my machine, strtoi("", base = 2L) produces NA_integer_
    > (which seems consistent with ?strtoi: "Values which cannot
    > be interpreted as integers or would overflow are returned
    > as NA_integer_").

indeed consistent with R's documentation on strtoi().
What machine would that be?

    > But on all the other machines I've seen, 0L is
    > returned. This seems to be consistent with the output of a
    > simple C program using the underlying strtol function (see
    > data.table link for this program, and for full
    > sessionInfo() of some environments with differing output).

    > So, what is the correct output of strtoi("", base = 2L)?

    > Is the cross-platform inconsistency to be
    > expected/documentable?

The inconsistency is certainly undesirable.
The relevant utility function in R's source (<R>/src/main/character.c)
is

static int strtoi(SEXP s, int base)
{
    long int res;
    char *endp;

    /* strtol might return extreme values on error */
    errno = 0;

    if(s == NA_STRING) return(NA_INTEGER);
    res = strtol(CHAR(s), &endp, base); /* ASCII */
    if(errno || *endp != '\0') res = NA_INTEGER;
    if(res > INT_MAX || res < INT_MIN) res = NA_INTEGER;
    return (int) res;
}

and so it clearly is a platform-inconsistency in the underlying C
library's strtol().

I think we should make this cross-platform consistent... and
indeed it make much sense to ensure the result of

   strtoi("", base=2L)  to become  NA_integer_

but changes are that would break code that has relied on the
current behavior {on "all but your computer" ;-)}  ?

    > Michael Chirico

Thank you for the report,

Martin Maechler
ETH Zurich and R Core Team