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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: printf and time_t
Date: Fri, 06 Feb 2026 02:59:01 -0800
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> David Brown <david.brown@hesbynett.no> writes:
> [...]
>
>> How many people do you know who have actually written and use a
>> C11 print system using _Generic and variadic macros?  I don't know
>> any.  (I've written simple examples as proofs of concept, posted
>> in this group, but not for real use.)  It turns out that people
>> /don't/ have to have workarounds.  "printf" has its limitations -
>> there's no doubt there.  But it is good enough for most people
>> and most uses.
>
> I recently played around with an attempted framework using _Generic.
> The goal was to be able to write something like
>
>     print(s(x), s(y), s(z));
>
> where x, y, and z can be of more or less arbitrary types (integer,
> floating-point char*).  The problem I ran into was that only one of
> the generic associations is evaluated (which one is determined at
> compile time), but *all* of them have to be valid code.

That is annoying but it shouldn't be too hard to work around
it.  To verify that hypothesis I wrote this test case:


        #include <stdio.h>
        #include <time.h>
        #include <stdint.h>

        #include "h/show.h"

        int
        main(){
          unsigned long long    ull     =  -1;
            signed long long    sll     =  -1;
          unsigned long         ul      =  -1;
            signed long         sl      =  -1;
          unsigned char         uc      =  -1;
            signed char         sc      =  -1;
          unsigned short        us      =  -1;
            signed short        ss      =  -1;
          unsigned int          ui      =  -1;
            signed int          si      =  -1;
            char                c       =  'q';
          float                 f       =  1.23;
          double                d       =  3.14159265358979312;
          double long           ld      =  6.28318530717958623;

          _Bool                 yes     =  1;
          _Bool                 no      =  !yes;

          clock_t               runtime =  clock();
          time_t                now     =  time(0);
          off_t                 offset  =  27;
          uint16_t              u16     =  -1;
           int16_t              s16     =  -1;
          uint_least32_t        uge32   =  -1;
           int_least32_t        sge32   =  -1;
          uint_fast32_t         uf32    =  -1;
           int_fast32_t         sf32    =  -1;
           char *               foo     =  "foo";
           const char   *       bas     =  "bas";

            show(
                uc,sc,us,ss,ui,si,ul,sl,ull,sll,
                c,f,d,ld,yes,no,u16,s16,uge32,sge32,
                runtime,now,offset,uf32,sf32,
                c * now / 1e8 * ld,
                foo, bas
            );
            printf( "\n" );

            return  0;
        }

which compiles under C11 and (along with the show.h include file)
produces output:

                  uc = 255
                  sc = -1
                  us = 65535
                  ss = -1
                  ui = 4294967295
                  si = -1
                  ul = 18446744073709551615
                  sl = -1
                 ull = 18446744073709551615
                 sll = -1
                   c = 'q'
                   f = 1.230000
                   d = 3.141593
                  ld = 6.283185
                 yes = true
                  no = false
                 u16 = 65535
                 s16 = -1
               uge32 = 4294967295
               sge32 = -1
             runtime = 365
                 now = 1770371790
              offset = 27
                uf32 = 18446744073709551615
                sf32 = -1
  c * now / 1e8 * ld = 12569.638642
                 foo = "foo"
                 bas = (const char *) "bas"