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From: Craig Franck <clfranck@worldnet.att.net>
Subject: Re: Porting Experiences (was Ada and Pascal etc )
Date: 1997/11/05
Message-ID: <63ok21$cjd@bgtnsc02.worldnet.att.net>#1/1
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References: <345E3ACD.A15@gsg.eds.com> <878648818snz@genesis.demon.co.uk>
 <345F9728.D61@gsg.eds.com>
Organization: AT&T WorldNet Services
Newsgroups: comp.lang.ada,comp.lang.c,comp.lang.c++
Date: 1997-11-05T00:00:00+00:00
List-Id: <comp.lang.ada>


"Shmuel (Seymour J.) Metz" <nospam@gsg.eds.com> wrote:
>Lawrence Kirby wrote:
>> 
>> The portability implications of this are small or non-existent (there may
>> be performace implications in rare circumstances, and issues relating to
>> data sizes and external data formats). As ever the C language is designed
>> with the assumption that the programmer knows what he is doing. The use
>> of ranges implies that you know beforehand what those ranges will be.
>> In C you follow a set of rules:
>> 
>> 1. If the range is contained within -32767 to 32767 then you use int
>> 
>> 2. If the range is contained within -2147483647 to 2147483647 then you
>>    use long.
>> 
>> 3. If you want to minimise space usage (such as for array elements or
>>    structure members) and the range is contained within -32767 to 32767 then
>>    you can use short. For -127 to 127 you can use signed char.
>> 
>> 4. The unsigned types have larger positive ranges if your range is
>>    non-negative. Notably unsigned char typically corresponds to the
>>    notion of "byte" in most languages.
>
>Those rules only apply if you are going from one 32-bit machine to
>another; they have nothing to do with the definition of C itself and are
>inapplicable when you have to move between different word sizes.

Huh? Those limits are contained in the standard. 

       5.2.4.2 Numerical limits. 
       ...
       5.2.4.2.1 Sizes of integral types <limits.h>
       ...
       Their implementation-defined values shall be equal or greater 
       in magnitude (absolute value) to those shown, with the same 
       sign.
       ...
       -- minimum value for an object of type int
       INT_MIN                                  -32767

       -- maximum value for an object of type int
       INT_MAX                                  +32767

>The C standard makes the size of an int implimentation dependent, and on
>16-bit machines it is normally 16. On 64-bit machines int is usually 64,
>and if you want 32 you specify short.

Yes, but portable ranges are defined by the standard, and that's 
what you should go by.

-- 
Craig
clfranck@worldnet.att.net
Manchester, NH
I try to take one day at a time, but sometimes several
days attack me at once. -- Ashleigh Brilliant