[Cfp-interest 3210] Re: Can nan() set errno?

[Jim Thomas]

> On Aug 14, 2024, at 3:28 PM, Fred J. Tydeman <tydeman at tybor.com> wrote:
> 
> On Wed, 14 Aug 2024 10:11:55 -0500 (COT) Fred J. Tydeman wrote:
>> 
>> Subject: [SC22WG14.26260] Can nan set errno?
> 
> 7.5 Errors <errno.h> has the general statement:
> 
> The value of errno may be set to nonzero by a library function call
> whether or not there is an error, provided the use of errno is not
> documented in the description of the function in this document.
> 
> 7.12.2 Treatment of error conditions has several specific statements
> that apply to all <math.h> functions.  So, overrides the 7.5 general
> statement. 
> 
> nan() is a <math.h> function, but is not a mathematical function.
> strtod() is not a <math.h> function; but it has words about
> overflow and underflow in the Returns section (that mirror 7.12.2).
> 
> So, what should happen for 
>  nan("a_very_long_string_________");
>  strtod("NAN(a_very_long_string_________)", nullptr);
> when the n-char-sequence is longer than what the nan returned can hold?

As stated in the strtod Description (7.24.2.6 #5), "the meaning of the n-char sequence is implementation-defined.” In particular, it does not need to be represented in the return NaN. An implementation is free to return the same NaN for all n-char sequences.

- Jim Thomas

> 
> 
> ---
> Fred J. Tydeman        Tydeman Consulting
> tydeman at tybor.com      Testing, numerics, programming
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