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Re: To use Perl like conditional assignment in C

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Ya Shou wrote:
) Hello,
)
)
) I want to assign an uncertain value to a variable, this variable with
) values in the configuration file, reads the configuration file
) through a function to return to the read configuration value, if not
) configured or the value of non-compliance, will return 0 for failure,
) when this, I will to give it a default value assigned.
)
) However, I found it seem impossible to achieve this in C, but much
) easier to implement in Perl, see below:
)
) cfgval = loadConfig () || DEFAULT_VAL;
)
) In C '||' operator does not return the value of the expression which
) is true, but returns 1 or 0, so that I can not be used in a similar
) way. I considered a program in C is:
)
) cfgval = loadConfig ()? loadConfig (): DEFAULT_VAL;
)
) And however, this approach to involve a duplication of code, it is
) ugly, the other will call loadConfig function twice, inefficient and
) likely to cause unnecessary accidents.
)
) Of course, if / else statement can achieve this functionality, but
) this method requires an additional variable, and not look simple. As
) follows:
)
) int loadval = loadConfig ();
) if (loadval! = 0) {
)    cfgval = loadval;
) } else {
)    cfgval = DEFAULT_VAL;
) }
)
) Or
)
) int loadval;
) cfgval = (loadval! = 0)? loadval: DEFAULT_VAL;
)
)
) I would like to ask you is, in this case, there is nothing more
) beautiful realization?

Why can't you assign to cfgval twice?

  if (!(cfgval = loadConfig()))
    cfgval = DEFAULT_VAL;

Or if you want to mimic the Perl style:

  (cfgval = loadConfig()) || (cfgval = DEFAULT_VAL);

But that will be deemed very ugly by most C programmers.

IIRC, some compilers have an extension which allows this:

  cfgval = loadConfig() ?: DEFAULT_VAL;

But that is not standard C, as far as I know.


SaSW, Willem
-- 
Disclaimer: I am in no way responsible for any of the statements
            made in the above text. For all I know I might be
            drugged or something..
            No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

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Thread

To use Perl like conditional assignment in C Ya Shou <shouyatf@gmail.com> - 2011-09-24 04:06 -0700
  Re: To use Perl like conditional assignment in C Willem <willem@toad.stack.nl> - 2011-09-24 11:13 +0000
  Re: To use Perl like conditional assignment in C pete <pfiland@mindspring.com> - 2011-09-24 07:48 -0400
    Re: To use Perl like conditional assignment in C Uno <merrilljensen@q.com> - 2011-09-24 21:58 -0700
      Re: To use Perl like conditional assignment in C pete <pfiland@mindspring.com> - 2011-09-25 08:44 -0400
        Re: To use Perl like conditional assignment in C Uno <merrilljensen@q.com> - 2011-09-26 21:52 -0700
          Re: To use Perl like conditional assignment in C pete <pfiland@mindspring.com> - 2011-09-27 21:14 -0400
            Re: To use Perl like conditional assignment in C Keith Thompson <kst-u@mib.org> - 2011-09-27 19:56 -0700
      Re: To use Perl like conditional assignment in C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-09-25 06:53 -0700
      Re: To use Perl like conditional assignment in C "J. J. Farrell" <jjf@bcs.org.uk> - 2011-09-26 04:40 +0100
  Re: To use Perl like conditional assignment in C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-24 09:04 -0400
    Re: To use Perl like conditional assignment in C Willem <willem@toad.stack.nl> - 2011-09-24 14:06 +0000
    Re: To use Perl like conditional assignment in C Ya Shou <shouyatf@gmail.com> - 2011-09-26 21:10 -0700
    Re: To use Perl like conditional assignment in C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-29 22:08 +0000
  Re: To use Perl like conditional assignment in C "BartC" <bc@freeuk.com> - 2011-09-26 01:37 +0100

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