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Re: C23 (C2x) changes

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From Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups comp.lang.c
Subject Re: C23 (C2x) changes
Date Mon, 27 Sep 2021 11:15:52 -0700
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Thiago Adams <thiago.adams@gmail.com> writes:
[...]
> Something new in C23 are attributes.
> One of then is nodiscard :
>
> http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2596.pdf
>
> "
> EXAMPLE 2
> [[nodiscard]] int important_func(void);
> void call(void) {
> int i = important_func();
> }
> No diagnostic for the call to important_func is encouraged despite the value of i not being used.
> "
> [[nodiscard("must check armed state")]]
> bool arm_detonator(int);
> void call(void) {
> arm_detonator(3);
> detonate();
> }
>
> "A diagnostic for the call toarm_detonator using the string literal "must check armed state" from the attribute argument
> clause is encouraged."
>
> This called my attention because the treatment is different for 
> int or _bool
> I have no idea why.

No, there's no difference in the treatment for int and _Bool.

The two relevant examples are:

    [[nodiscard]] int important_func(void);
    void call(void) {
        int i = important_func();
    }

    No diagnostic for the call to important_func is encouraged despite
    the value of i not being used.

and

    [[nodiscard("must check armed state")]]
    bool arm_detonator(int);
    void call(void) {
        arm_detonator(3);
        detonate();
    }

    A diagnostic for the call to arm_detonator using the string literal
    "must check armed state" from the attribute argument clause is
    encouraged.

The difference isn't the types, it's the way the result is used.  In the
first example, the result of the function is used to initialize an
object, so it's "used", even though that object's stored value is never
used.  In the second example, the result isn't assigned to anything.
The point is that compilers aren't required to do data flow analysis;
any immediate use of the result is enough to turn off the warning.  (Of
course compilers can warn about anything they like, and compilers
commonly do warn about unused variables, but that warning isn't
connected to the [[nodiscard]] attribute.)

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

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Thread

C23 (C2x) changes Mehdi Amini <atorrses@gmail.com> - 2021-09-20 10:54 +0430
  Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 09:35 +0200
    Re: C23 (C2x) changes Mehdi Amini <atorrses@gmail.com> - 2021-09-21 11:01 +0430
  Re: C23 (C2x) changes John Bode <jfbode1029@gmail.com> - 2021-09-20 10:41 -0500
    Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 18:17 +0200
      Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 18:55 +0100
        Re: C23 (C2x) changes scott@slp53.sl.home (Scott Lurndal) - 2021-09-20 18:21 +0000
        Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 21:39 +0200
          Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 21:07 +0100
            Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 22:59 +0200
              Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 22:29 +0100
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-20 17:43 -0700
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-21 17:56 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-21 18:05 +0100
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-21 11:42 -0700
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-22 11:37 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-22 11:55 +0100
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-22 14:21 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-22 13:58 +0100
                Re: C23 (C2x) changes Ian Pilcher <arequipeno@gmail.com> - 2021-09-22 12:02 -0500
                Re: C23 (C2x) changes scott@slp53.sl.home (Scott Lurndal) - 2021-09-22 17:19 +0000
          Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 23:05 +0100
            Re: C23 (C2x) changes scott@slp53.sl.home (Scott Lurndal) - 2021-09-20 22:47 +0000
              Re: C23 (C2x) changes Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-09-20 22:58 +0000
              Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-02 07:16 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 15:15 +0000
            Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-20 17:45 -0700
        Re: C23 (C2x) changes Manfred <noname@add.invalid> - 2021-09-27 17:15 +0200
          Re: C23 (C2x) changes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-27 17:38 +0100
            Re: C23 (C2x) changes Manfred <noname@add.invalid> - 2021-09-27 23:18 +0200
              Re: C23 (C2x) changes antispam@math.uni.wroc.pl - 2021-09-28 13:53 +0000
              Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-02 08:07 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 15:18 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-02 15:04 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 01:58 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-02 22:06 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 10:43 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-03 13:30 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 05:04 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-03 23:24 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 06:54 +0000
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-04 09:58 +0200
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 15:52 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-04 10:45 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 20:30 +0000
                Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-06 03:57 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-06 12:27 +0000
          Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-29 03:38 +0000
      Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-15 11:35 +0100
        Re: C23 (C2x) changes Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-10-15 18:27 +0000
          Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-15 20:08 +0100
          Re: C23 (C2x) changes Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-10-15 19:20 +0000
            Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-15 21:50 +0100
    Re: C23 (C2x) changes Florian Weimer <fw@deneb.enyo.de> - 2021-10-03 09:43 +0200
      Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-03 18:53 +0200
      Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-03 13:55 -0700
  Re: C23 (C2x) changes William Ahern <william@25thandClement.com> - 2021-09-21 22:57 -0700
    Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-02 08:55 -0700
      Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 16:36 +0000
  Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-09-22 20:27 +0200
    Re: C23 (C2x) changes Philipp Klaus Krause <pkk@spth.de> - 2021-09-22 22:25 +0200
      Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-22 14:05 -0700
        Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-22 23:24 +0100
          Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-22 18:49 -0700
        Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-09-23 18:47 +0200
  Static bounds checking (was Re: C23 (C2x) changes) William Ahern <william@25thandClement.com> - 2021-09-23 21:11 -0700
    Re: Static bounds checking (was Re: C23 (C2x) changes) David Brown <david.brown@hesbynett.no> - 2021-09-24 08:51 +0200
      Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-24 09:30 +0200
    Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-24 07:52 +0000
      Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-24 12:32 +0200
        Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-24 10:49 +0000
          Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-24 14:46 +0200
      Re: Static bounds checking (was Re: C23 (C2x) changes) Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-24 18:14 +0200
        Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 01:00 +0000
          Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-25 07:44 +0200
            Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 11:28 +0000
            Re: Static bounds checking (was Re: C23 (C2x) changes) antispam@math.uni.wroc.pl - 2021-09-28 10:56 +0000
          Re: Static bounds checking (was Re: C23 (C2x) changes) Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 09:48 +0200
            Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 11:30 +0000
              Re: Static bounds checking (was Re: C23 (C2x) changes) Kaz Kylheku <480-992-1380@kylheku.com> - 2021-09-25 20:49 +0000
                Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-26 00:04 +0000
              Re: Static bounds checking (was Re: C23 (C2x) changes) Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-26 06:56 +0200
  Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-27 10:15 -0700
    Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-27 11:15 -0700
      Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-27 22:11 +0200
      Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-27 14:20 -0700
        Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-27 14:31 -0700
      Re: C23 (C2x) changes Mehdi Amini <atorrses@gmail.com> - 2021-09-28 10:43 +0330
  Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-06 04:01 -0700
    Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-10-06 04:42 -0700
      Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-29 04:04 -0700
        Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-29 16:34 +0200
    Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-06 19:07 +0200
      Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-07 11:06 +0200
        Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-07 19:31 +0200
          Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-07 22:14 +0200
            Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-10-08 06:18 -0700
              Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-10-08 06:21 -0700
      Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-29 04:01 -0700
    Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-15 12:59 +0200
      Re: C23 (C2x) changes Jim Jackson <jj@franjam.org.uk> - 2021-10-15 16:50 +0000
        Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-16 07:51 +0200
          Re: C23 (C2x) changes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-16 11:50 -0700
            Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-16 21:28 +0200
              Re: C23 (C2x) changes Jim Jackson <jj@franjam.org.uk> - 2021-10-17 17:18 +0000
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-17 20:00 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-17 19:17 +0100
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-18 06:49 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-18 11:23 +0100
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-18 14:09 +0200
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-21 01:07 +0000
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-21 01:02 +0000
          Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-16 21:28 +0200
            Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-17 06:04 +0200
              Re: C23 (C2x) changes Manfred <noname@add.invalid> - 2021-10-17 19:35 +0200
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-17 20:01 +0200
                Re: C23 (C2x) changes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-17 14:15 -0700
              Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-21 01:02 +0000
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-21 13:15 +0200

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