Questions about NCEG

[Jim Kingdon]

eggert at twinsun.com (Paul Eggert) writes:

    >While we're on the subject, NCEG should provide for a way for a program to
    >print a number so that it can be read back.  ANSI C's "C" locale requires
    >that an IEEE 754 implementation's scanf() cannot read some numbers that
    >its printf() should be able to output, namely infinities and NaNs.

gwyn at smoke.BRL.MIL (Doug Gwyn) writes:

    No, any use of NaNs and Infinities lies in the realm of undefined or
    implementation-defined behavior, and thus is not constrained by the
    C standard.

Unless I'm misreading something, in the "C" locale,

    scanf ("%f", &x);

where the input contains

    NaN

has to return zero without reading any of the characters "NaN".
Picking an alternate syntax like "0rnan" or something which is
supposed to be more number-like doesn't help, as section 4.10.1.4 is
very specific about what a number as input to strtod() (or scanf()) is
supposed to look like.

In another locale, the implementation is allowed to recognize other
forms, so presumably NCEG wants to standardize a "NUMERIC" locale.