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Re: int vs. unsigned int vs. size_t

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On 05/ 1/11 04:27 AM, Tim Prince wrote:
> On 4/29/2011 11:40 PM, Steve Keller wrote:
>> This is a style question.  To iterate through an array I often use
>> code similar to the following:
>>
>> 	#define ASIZE(a) (sizeof(a) / sizeof((a)[0])
>> 	int a[] = { ... };
>>
>> 	void foo(void)
>> 	{
>> 		int i;
>> 		for (i = 0; i<   ASIZE(a); i++)
>> 			/* do something with a[i]. */
>> 	}
>>
>> With all warnings enabled, gcc will warn about a comparison between
>> signed and unsigned integer types, because sizeof() yields a size_t
>> which is unsigned.  To eliminate that warning I could use unsigned int
>> or size_t for the variable i.  But IMO int feels most natural and
>> size_t might have unwanted overhead, if it is a large integer type and
>> I know that the array size will be very small (i.e. less than INT_MAX
>> elements).
>>
>> So, what type for i do you prefer in cases like this?
>>
> How about defining a loop invariant for the loop test, with matching
> data type?
>    		int i, ilimit=ASIZE(a);
>    		for (i = 0; i<   ilimit; i++)
>
> If your compiler performs optimizations based on countability of the for
> loop, this avoids uncertainty there too.

There already is one: (sizeof(a) / sizeof((a)[0]) is a compile time 
constant.

-- 
Ian Collins

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int vs. unsigned int vs. size_t Steve Keller <keller@no.invalid> - 2011-04-30 08:40 +0200
  Re: int vs. unsigned int vs. size_t Tim Prince <tprince@computer.org> - 2011-04-30 09:27 -0700
    Re: int vs. unsigned int vs. size_t Tim Prince <tprince@computer.org> - 2011-04-30 12:55 -0700
    Re: int vs. unsigned int vs. size_t Ian Collins <ian-news@hotmail.com> - 2011-05-01 10:34 +1200
  Re: int vs. unsigned int vs. size_t pozz <pozzugno@gmail.com> - 2011-04-30 19:33 +0200
    Re: int vs. unsigned int vs. size_t Ian Collins <ian-news@hotmail.com> - 2011-05-01 09:03 +1200
      Re: int vs. unsigned int vs. size_t Tim Prince <tprince@computer.org> - 2011-04-30 14:34 -0700
        Re: int vs. unsigned int vs. size_t Ian Collins <ian-news@hotmail.com> - 2011-05-01 10:37 +1200
  Re: int vs. unsigned int vs. size_t Datesfat Chicks <datesfat.chicks@gmail.com> - 2011-04-30 19:41 -0400
    Re: int vs. unsigned int vs. size_t Keith Thompson <kst-u@mib.org> - 2011-04-30 17:46 -0700
      Re: int vs. unsigned int vs. size_t Datesfat Chicks <datesfat.chicks@gmail.com> - 2011-05-01 21:27 -0400
  Re: int vs. unsigned int vs. size_t Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-04-30 22:23 -0700
  Re: int vs. unsigned int vs. size_t Dr Nick <3-nospam@temporary-address.org.uk> - 2011-05-01 14:16 +0100
    Re: int vs. unsigned int vs. size_t Barry Schwarz <schwarzb@dqel.com> - 2011-05-01 10:31 -0700
    Re: int vs. unsigned int vs. size_t Keith Thompson <kst-u@mib.org> - 2011-05-01 12:25 -0700
      Re: int vs. unsigned int vs. size_t James Kuyper <jameskuyper@verizon.net> - 2011-05-01 20:00 -0400
        Re: int vs. unsigned int vs. size_t Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-02 10:17 -0700
      Re: int vs. unsigned int vs. size_t Dr Nick <3-nospam@temporary-address.org.uk> - 2011-05-02 08:37 +0100
  Re: int vs. unsigned int vs. size_t ImpalerCore <jadill33@gmail.com> - 2011-05-03 06:02 -0700
    Re: int vs. unsigned int vs. size_t Peter Nilsson <airia@acay.com.au> - 2011-05-03 15:55 -0700
    Re: int vs. unsigned int vs. size_t Luca Forlizzi <luca.forlizzi@gmail.com> - 2011-05-05 02:38 -0700
      Re: int vs. unsigned int vs. size_t ImpalerCore <jadill33@gmail.com> - 2011-05-05 06:37 -0700
        Re: int vs. unsigned int vs. size_t Angel <angel+news@spamcop.net> - 2011-05-05 16:10 +0000
        Re: int vs. unsigned int vs. size_t Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-05-05 09:35 -0700
          Re: int vs. unsigned int vs. size_t Keith Thompson <kst-u@mib.org> - 2011-05-05 11:22 -0700
            Re: int vs. unsigned int vs. size_t Peter Nilsson <airia@acay.com.au> - 2011-05-05 16:06 -0700
            Re: int vs. unsigned int vs. size_t Michael Press <rubrum@pacbell.net> - 2011-05-06 02:32 -0700
        Re: int vs. unsigned int vs. size_t Luca Forlizzi <luca.forlizzi@gmail.com> - 2011-05-07 02:42 -0700

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