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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:
>
> [... 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.

-- 
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 */

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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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