[Cfp-interest 3195] Fwd: [SC22WG14.26260] Can nan set errno?

[Fred J. Tydeman]

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From: Richard Smith <richardsmith at google.com>
To: ISO C <sc22wg14 at open-std.org>
Date: Fri, 2 Aug 2024 16:32:14 -0700
Subject: [SC22WG14.26260] Can nan set errno?

Hi,

The documentation of errno is clear that it can be set to any non-zero
value by a function whose specification doesn't mention errno. The
specification of nan doesn't mention errno. Therefore one might conclude
that nan can choose to set errno to any non-zero value.

However, the specification of nan says that it's equivalent to a call to
strtod, and the specification of strtod *does* mention errno, which
presumably means that the strtod call that a call to nan is equivalent to
must leave errno unchanged (the condition for setting errno to ERANGE is
presumably not met since a NAN value should presumably not be considered to
overflow even if the n-char-sequence doesn't fit in the payload).

So which interpretation wins? Is a call to nan really equivalent to a call
to strtod, or is it allowed to affect errno? (There's a similar situation
for atof, but it explicitly mentions errno in its specification to say that
it may or may not have strtod's effect on errno, so the rule from 7.5/3
that it may be set to any non-zero value doesn't apply.)

Thanks!
Richard

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Fred J. Tydeman        Tydeman Consulting
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