[Info-vax] C limitations, was: Re: VMS process communication

[Arne Vajhøj]

On 4/22/2023 7:47 PM, Arne Vajhøj wrote:
> On 4/20/2023 5:32 AM, Johnny Billquist wrote:
>> On 2023-04-16 19:26, Arne Vajhøj wrote:
>>> On 4/12/2023 9:33 PM, Johnny Billquist wrote:
>>>> On 2023-04-12 16:44, Arne Vajhøj wrote:
>>>>> On 4/12/2023 10:41 AM, Arne Vajhøj wrote:
>>>>>> On 4/7/2023 4:58 PM, Johnny Billquist wrote:
>>>>>>> On 2023-04-03 14:31, bill wrote:
>>>>>>>> On 4/2/2023 8:50 PM, Johnny Billquist wrote:
>>>>>>>>> On 2023-03-29 19:51, bill wrote:
>>>>>>>>>> Weird?  What about under Primos where chars always have the 
>>>>>>>>>> high order
>>>>>>>>>> bit turned on?  It was called "mark memory parity" but it 
>>>>>>>>>> never made any
>>>>>>>>>> sense to me when I had to work with it.  :-)
>>>>>>>>>
>>>>>>>>> I think/suspect that this goes outside the scope of C...
>>>>>>>>
>>>>>>>> Of course it does.  But it affects C a lot more than other 
>>>>>>>> languages
>>>>>>>> if for no other reason than programming style.  How many Unix C 
>>>>>>>> programs
>>>>>>>> have you seen where parsing is done by looking at the value of a 
>>>>>>>> letter
>>>>>>>> as opposed to just comparing chars?  Even with Primix porting a 
>>>>>>>> Unix
>>>>>>>> program to a Pr1me was a serious task and often not even possible.
>>>>>>>
>>>>>>> I don't understand what you mean. Are you just talking about some 
>>>>>>> people assuming you have ASCII, and looking at the decimal 
>>>>>>> values, instead of the character representation. Basically 
>>>>>>> writing 65 instead of 'A'?
>>>>>>> If so, that is certainly something I've seen in lots of 
>>>>>>> languages, and are in fact much more an issue in most other 
>>>>>>> languages that I've used, since they do not consider a thing like 
>>>>>>> 'A' to be a numeric value. C doing that really helps in this 
>>>>>>> context.
>>>>>>>
>>>>>>> I'd say it's more common to see C code using the characters 
>>>>>>> instead of their numeric representation just because it is so 
>>>>>>> easy to do in C.
>>>>>>
>>>>>> I believe there are basically two groups of languages:
>>>>>>
>>>>>> A) those where one can write both c=='A' and c==65
>>>>>> B) those where one can write c=='A' but c==65 gives a compile 
>>>>>> error and has to be written as ord(c)==65
>>>>>>
>>>>>> I find it more likely that group A will use 65 than group B.
>>>>>
>>>>> Examples of code:
>>>>
>>>> [...lots of code deleted...]
>>>>
>>>> The problem with this is that it is very artificial, and designed to 
>>>> prove your point.
>>>
>>> Testing if a char is in the digit range is not an artificial problem.
>>>
>>> Yes - the example was showing my point - it would have
>>> been pretty weird if I had produced an example that did
>>> not show my point.
>>
>> The problem is that it is very artificial.
>> First of all, I've never seen C code where people would write
>>
>> if ((x < 48) || (57 < x)) { ... }
>>
>> It's just plain stupid to write that if they want to check if it is a 
>> digit. It's close to unreadable, and just makes much more sense to say 
>> '0' and '9'.
>>
>> But secondly, noone in C would/should ever even do such a stupid 
>> thing. There are isdigit() for exactly this, and basically any other 
>> categorization you would want to do, so even more so, the suggested 
>> bad way of doing it in C is not something anyone would/should do.
>>
>> And using a function like isdigit() is actually way better than 
>> checking if the character is between '0' and '9', even in other 
>> languages. Since it actually also removes the possible risks that you 
>> might have a character set where they are not consecutive values. Your 
>> code is already making bad assumptions, and in most languages you are 
>> actually force to stick with those assumptions.
>>
>> In C, you are not, and should actually not write this kind of code. It 
>> is potentially bad and non-portable in all kind of weird ways.
>>
>> That is why you have libraries that provide the proper evaluation of 
>> such issues, and which makes the code safer.
>>
>> So in the end, I definitely think C does this better than your other 
>> languages selected.
> 
> True. In C the isdigit function would be much better than a range check.
> 
> Some other languages have similar functions, but not necessarily
> doing what the programmer want.
> 
> Java has a Character.isDigit method that return true for 350 chars.
> But I am pretty sure that most Java developers are interested in
> knowing if the char is in 0..9 not whether it is among those 350 chars.

Of course C also got iswdigit - which on my system return true
for 263 input values.

But I don't think w is that popular in C.

Arne