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Groups > comp.lang.c > #41342

Few questions about casting away const.

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const char *s = "abc";
char *t = s;

printf("%s", s);


Firstly, the direct cast from 'const char *' to 'char *' which is seen on 
the second line. I've read that this is illegal in standard C, is that 
true?

Secondly, given that printf's 's' specifier matches a 'char *', the 
comment in section 6.5.2.2p6 of C11 seems to indicate that these types 
are interchangeable in this situation. If the direct cast is invalid, 
would this be a legal alternative?:


#define unconst(p) (unconst_(0, p))

char *unconst_(int unused, ...)
{
        va_list args;
        char *r;

        va_start(args, unused);
        r = va_arg(args, char *);
        va_end(args);
        return r;
}
 
const char *s = "abc";
char *t = unconst(s);


Or, are there other possibilities?

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Few questions about casting away const. Daniel <daniel@inventati.org> - 2014-03-04 11:18 +0000
  Re: Few questions about casting away const. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-04 12:39 +0000
  Re: Few questions about casting away const. Kaz Kylheku <kaz@kylheku.com> - 2014-03-04 17:05 +0000
  Re: Few questions about casting away const. Keith Thompson <kst-u@mib.org> - 2014-03-04 10:16 -0800
    Re: Few questions about casting away const. Daniel <daniel@inventati.org> - 2014-03-05 03:45 +0000
      Re: Few questions about casting away const. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-05 04:20 +0000
  Re: Few questions about casting away const. James Kuyper <jameskuyper@verizon.net> - 2014-03-04 15:18 -0500
    Re: Few questions about casting away const. Daniel <daniel@inventati.org> - 2014-03-05 04:14 +0000
      Re: Few questions about casting away const. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-05 04:35 +0000
        Re: Few questions about casting away const. Daniel <daniel@inventati.org> - 2014-03-05 06:11 +0000
          Re: Few questions about casting away const. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-05 12:14 +0000
            Re: Few questions about casting away const. Daniel Harrison <daniel@inventati.org> - 2014-03-07 04:31 +0000
              Re: Few questions about casting away const. Barry Schwarz <schwarzb@dqel.com> - 2014-03-06 21:23 -0800
                Re: Few questions about casting away const. Kaz Kylheku <kaz@kylheku.com> - 2014-03-07 05:59 +0000
              Re: Few questions about casting away const. James Kuyper <jameskuyper@verizon.net> - 2014-03-07 07:18 -0500
              Re: Few questions about casting away const. Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-10 00:30 -0700
                Re: Few questions about casting away const. Keith Thompson <kst-u@mib.org> - 2014-03-10 09:00 -0700
                Re: Few questions about casting away const. Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-10 11:13 -0700
                Re: Few questions about casting away const. Keith Thompson <kst-u@mib.org> - 2014-03-10 12:10 -0700
                Re: Few questions about casting away const. Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 07:38 +0000
                Re: Few questions about casting away const. Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 09:02 -0700
          Re: Few questions about casting away const. Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-10 02:29 -0700
            Re: Few questions about casting away const. Keith Thompson <kst-u@mib.org> - 2014-03-10 10:52 -0700
              Re: Few questions about casting away const. Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 08:50 -0700

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