Re: I need help understand some c code

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: I need help understand some c code
Date	2020-12-23 12:05 -0800
Organization	None to speak of
Message-ID	<87ft3w9tkp.fsf@nosuchdomain.example.com> (permalink)
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scott@slp53.sl.home (Scott Lurndal) writes:
> T <T@invalid.invalid> writes:
>>On 12/21/20 5:11 AM, Bart wrote:
>>> time_t'
>>
>>What I was after was what type of variable that was.  How
>>many bits etc..  But I don't need it anymore as I was
>>mistaken that I was not addressing a .so or .dll.
>>
>>> Also I use WinAPI for the time. Here's an example of calling Windows' 
>>> GetSystemTime()
>>
>>Now that I can also use as an example of how to get
>>the time on both Windows and Linux.
>
> Although the time(2) system call has been replaced by
> the gettimeofday(2) system call which offers microsecond
> resolution instead of second resolution.
>
>    https://pubs.opengroup.org/onlinepubs/9699919799/functions/gettimeofday.html

It hasn't been "replaced".  time() is defined by both ISO C and POSIX.
gettimeofday() is defined by POSIX -- and has been marked obsolescent
as of POSIX Issue 7.

C17 adds timespec_get, which gives you the current time with nanosecond
precision (but not necessarily nanosecond accuracy).

> Both system calls have been augmented by the POSIX
> clock functions (clock_getres, clock_gettime, clock_settime)
> which support multiple clock sources and have nanosecond resolution.
>
>    https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock_gettime.html
>
> The 'type' of time_t (insofar as any portable application is concerned):
>
>    https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/time.h.html
>
> There you'll find these statements about the characteristics of 'time_t':
>
>    "All of the types shall be defined as arithmetic types
>     of an appropriate length"
>
>    "clock_t shall be an integer or real-floating type.  time_t shall
>    be an integer type."
>
> Many platforms typedef 'time_t' as long.

POSIX places stricter requirements on time_t than ISO C does.
C only requires time_t to be a real (integer or floating) type
"capable of representing times".  It doesn't even require that
increasing values represent increasing times.

Most platforms typedef time_t as a signed integer type of 32 or, if
possible, 64 bits, representing seconds since the epoch (1970-01-01
00:00:00 UTC).  (Windows has 32-bit long, so I believe it defines
time_t as long long.)  A conforming implementation could define time_t
as a floating-point type, but I'm not aware of any that do so.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */

Thread

I need help understand some c code T <T@invalid.invalid> - 2020-12-20 18:32 -0800
  Re: I need help understand some c code Siri Cruise <chine.bleu@yahoo.com> - 2020-12-20 19:03 -0800
  Re: I need help understand some c code Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-12-20 19:56 -0800
    Re: I need help understand some c code T <T@invalid.invalid> - 2020-12-20 20:02 -0800
      Re: I need help understand some c code Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-12-20 20:43 -0800
        Re: I need help understand some c code T <T@invalid.invalid> - 2020-12-20 21:06 -0800
          Re: I need help understand some c code Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-12-20 21:56 -0800
  Re: I need help understand some c code T <T@invalid.invalid> - 2020-12-20 20:33 -0800
    Re: I need help understand some c code Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-12-20 20:51 -0800
      Re: I need help understand some c code T <T@invalid.invalid> - 2020-12-20 21:11 -0800
        Re: I need help understand some c code Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-12-20 22:10 -0800
          Re: I need help understand some c code T <T@invalid.invalid> - 2020-12-20 22:15 -0800
      Re: I need help understand some c code Bart <bc@freeuk.com> - 2020-12-21 13:11 +0000
        Re: I need help understand some c code T <T@invalid.invalid> - 2020-12-21 13:47 -0800
          Re: I need help understand some c code scott@slp53.sl.home (Scott Lurndal) - 2020-12-23 17:18 +0000
            Re: I need help understand some c code Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-12-23 12:05 -0800
        Re: I need help understand some c code T <T@invalid.invalid> - 2020-12-21 14:25 -0800
  Re: I need help understand some c code Bonita Montero <Bonita.Montero@gmail.com> - 2020-12-21 05:45 +0100
  Re: I need help understand some c code Bart <bc@freeuk.com> - 2020-12-21 12:16 +0000
  Re: I need help understand some c code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-12-21 20:03 +0000

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