Path: ...!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: Geoff Clare <geoff@clare.See-My-Signature.invalid>
Newsgroups: comp.lang.awk
Subject: Re: Y2K38 bug (January 19, 2038)
Date: Wed, 13 Mar 2024 13:46:30 +0000
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Keith Thompson wrote:

> Christian Weisgerber <naddy@mips.inka.de> writes:
>> On 2024-03-12, Geoff Clare <geoff@clare.See-My-Signature.invalid> wrote:
>>> Also, having signed time_t doesn't necessarily mean that dates before
>>> Jan 1970 are supported.
>>
>> mktime(3) is documented to return (time_t)-1 in case of error, which
>> bodes ill for Dec 31, 1969, 23:59:59 UTC.
> 
> It can still return a correct value of -1.  It does make it difficult
> for the caller to determine whether a -1 return value denotes an error
> or not.

C23 has introduced a way to distinguish the cases.  It says:

    [on error] the function returns the value (time_t)(-1) and does
    not change the value of the tm_wday component of the structure.

This will also be in the forthcoming POSIX.1 revision, which adds
this advice:

    Since (time_t)−1 is a valid return value for a successful call to
    mktime(), an application wishing to check for error situations
    should set tm_wday to a value less than 0 or greater than 6 before
    calling mktime(). On return, if tm_wday has not changed an error
    has occurred.

-- 
Geoff Clare <netnews@gclare.org.uk>