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Re: #include <stdint.h>

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Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>> [... on printing various integer types ...]
>>>
>>>> Using the macros:
>>>>
>>>> #include <stdio.h>
>>>> // #include <stdint.h>
>>>> #include <inttypes.h>
>>>> #include <limits.h>
>>>>
>>>> int main(void) {
>>>>     printf("INT_MAX : %d\n", INT_MAX);
>>>>     printf("INT_MIN : %d\n", INT_MIN);
>>>>     printf("LONG_MAX : %ld\n", LONG_MAX);
>>>>     printf("LONG_MIN : %ld\n", LONG_MIN);
>>>>     printf("UINT_MAX : %u\n", UINT_MAX);
>>>>     printf("ULONG_MAX : %lu\n", ULONG_MAX);
>>>>     printf("USHRT_MAX : %u\n", (unsigned)USHRT_MAX);
>>>
>>> The cast in the last line is not needed.
>>>
>>>>     printf("\nFrom stdint.h: \n");
>>>>     printf("INT8_MAX : %" PRId8 "\n", INT8_MAX);
>>>>     printf("INT16_MAX : %" PRId16 "\n", INT16_MAX);
>>>>     printf("INT32_MAX : %" PRId32 "\n", INT32_MAX);
>>>>     printf("INT64_MAX : %" PRId64 "\n", INT64_MAX);
>>>>     printf("UINT8_MAX : %" PRIu8 "\n", UINT16_MAX);
>>>>     printf("UINT16_MAX : %" PRIu16 "\n", UINT16_MAX);
>>>>     printf("UINT32_MAX : %" PRIu32 "\n", UINT32_MAX);
>>>>     printf("UINT64_MAX : %" PRIu64 "\n", UINT64_MAX);
>>>> }
>>>>
>>>> Most of the casts in your original program are unnecessary, since
>>>> the expressions are already of the type you were casting them to.
>>>> But unsigned short could promote either to signed int or to
>>>> unsigned int, depending on their ranges, so converting to unsigned
>>>> and using "%u" is appropriate.  In general, when passed to a
>>>> variadic function like printf, an argument of an integer type
>>>> narrower than int is promoted to int if type's range fits in int,
>>>> to unsigned int otherwise.
>>>
>>> The description of how type promotion works is right, however a
>>> cast is still not needed there.  The reason is that values given
>>> as variadic arguments are allowed to be the corresponding signed
>>> or unsigned version of the type used to get the value, and that
>>> will work as long as the value is in the set of values common to
>>> both types.  If an unsigned short promotes to int, then its value
>>> is guaranteed to be in the set of values representable by both
>>> int and unsigned int, and hence using %u for an uncasted unsigned
>>> short is always safe.
>>
>> My reading of the standard is that that's certainly the intent, but
>> it's not quite stated explicitly.
>>
>> N1570 6.5.2.2 makes a similar guarantee for calls to a function defined
>> without a prototype.
>>
>> 7.16.1.1 makes the same guarantee for arguments to the va_arg macro,
>> which makes it clear that printf("%u\n", 1) is *supposed* to work, but I
>> don't see a guarantee that the call itself (which happens before va_arg
>> is invoked -- assuming printf even uses va_arg) has defined behavior.
>>
>> Or I'm missing something.
>
> I wrote a long reply to Ben Bacarisse in this same thread, you
> may want to read that reply in addition to what I write here.
>
> Basically the question boils down to what is meant by the
> somewhat vague phrase "the correct type".  I believe that phrase
> is meant to refer to the rules of 7.16.1.1.  If you want to say
> there's an ambiguity about what is meant, certainly I could agree
> with that.  For purposes of posting in comp.lang.c, my usual rule
> is to judge the language according to what meaning is intended,
> and since here we are in agreement about what is intended here we
> are not in conflict.  Whether the C standard "actually says" that
> the va_arg rules apply to *printf functions is, I think, not
> an answerable question, and in any case not really a useful
> question for purposes of comp.lang.c.  I am glad we agree about
> what rule is intended, and IMO that is really all that matters
> for the present discussion.

I mostly agree, but I disagree with your statement about the va_arg
rules applying to *printf.

The standard doesn't say that the *printf functions use va_arg.  The
question of whether the standard *actually says* that va_arg rules apply
to *printf functions is, I think, answerable, and the answer is no.

Whether that matters is another question, but surely a question about
whether the standard says something can be resolved by reading the
standard.

-- 
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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#include <stdint.h> SIMON <invalid@invalid.invalid> - 2021-06-13 23:08 +0100
  Re: #include <stdint.h> Bart <bc@freeuk.com> - 2021-06-13 23:27 +0100
    Re: #include <stdint.h> Bart <bc@freeuk.com> - 2021-06-13 23:57 +0100
      Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 09:03 +0200
        Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-14 01:23 -0700
          Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 12:31 +0200
        Re: #include <stdint.h> Bart <bc@freeuk.com> - 2021-06-14 11:54 +0100
  Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-06-13 18:34 -0400
  Re: #include <stdint.h> Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-06-13 23:34 +0100
  Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-13 17:48 -0700
    Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 09:09 +0200
      Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-14 01:24 -0700
        Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 12:30 +0200
    Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-24 10:31 -0700
      Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-24 11:28 -0700
        Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-11 02:49 -0700
          Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-11 15:30 -0700
            Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-16 03:33 -0700
              Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-16 12:31 -0700
                Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-09-30 07:07 -0700
                Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-30 08:42 -0700
                Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-06 03:55 -0700
                Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-06 07:06 -0700
                Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-06 11:47 -0400
        Re: #include <stdint.h> Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-10-06 09:35 -0700
          Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-06 10:06 -0700
          Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-06 17:40 -0400
            Re: #include <stdint.h> Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-06 22:14 +0000
              Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-06 20:06 -0400
                Re: #include <stdint.h> Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-07 02:15 +0000
      Re: #include <stdint.h> Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-06-24 22:34 +0100
        Re: #include <stdint.h> Öö Tiib <ootiib@hot.ee> - 2021-06-24 15:01 -0700
          Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-24 15:26 -0700
        Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-11 02:14 -0700

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