[tz] mktime() clarification

[Clive D.W. Feather]

Dag-Erling Smrgrav said:
> "Clive D.W. Feather via tz" <tz at iana.org> writes:
> > Dag-Erling Smørgrav <des at des.no> writes:
> > > [...] POSIX never guarantees that a successful call does not modify
> > > errno [...]
> > Library functions and system calls never set errno to 0. So the usual
> > answer is to set errno to 0 before the call and see if it's still 0
> > afterwards.
> 
> See above, and try this:
> 
>     struct tm tm = { .tm_mday = 1, .tm_year = 69 };
>     errno = 0;
>     printf("%ld %d\n", mktime(&tm), errno);

There is no requirement in the C99 Standard (I dropped out of WG14 shortly
after) that the call to mktime is made before the value of errno is read.

-- 
Clive D.W. Feather          | If you lie to the compiler,
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