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

[Arne Vajhøj]

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.

Arne