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Groups > comp.lang.c > #382726
| From | Keith Thompson <Keith.S.Thompson+u@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Is C ready to become a safer language? |
| Date | 2024-02-18 15:28 -0800 |
| Organization | None to speak of |
| Message-ID | <87sf1p5p3h.fsf@nosuchdomain.example.com> (permalink) |
| References | (2 earlier) <865xyw62av.fsf@linuxsc.com> <877cjbdfg3.fsf@nosuchdomain.example.com> <86frxz4g9l.fsf@linuxsc.com> <87a5o7ber9.fsf@nosuchdomain.example.com> <86zfw62kd8.fsf@linuxsc.com> |
Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>>> [snip discussion of a program that divides by zero]
>>>>
>>>>> An implementation can refuse to translate the program, but not
>>>>> because undefined behavior occurs. The undefined behavior here
>>>>> happens only when the program is executed, but just compiling the
>>>>> program doesn't do that. No execution, no undefined behavior.
>>>>> Still the program may be rejected, because it is not strictly
>>>>> conforming (by virtue of having output depend on the undefined
>>>>> behavior if the program is ever run).
>>>>
>>>> Just to be clear, would you say that a conforming hosted
>>>> implementation may reject this program:
>>>>
>>>> #include <limits.h>
>>>> #include <stdio.h>
>>>> int main(void) {
>>>> printf("INT_MAX = %d\n", INT_MAX);
>>>> }
>>>>
>>>> solely because it's not strictly conforming?
>>>
>>> My understanding of the C standard is that a hosted implementation
>>> may choose not to accept the above program and still be conforming,
>>> because this program is not strictly conforming. (Please assume
>>> subsequent remarks always refer to implementations that are both
>>> hosted and conforming.)
>>>
>>> Also, assuming we have ruled out cases involving #error, a
>>> conforming implementation may choose not to accept a given program
>>> if and only if the program is not strictly conforming. Being
>>> strictly conforming is the only criterion that matters (again
>>> assuming there is no #error) in deciding whether an implementation
>>> may choose not to accept the program in question.
>>>
>>> I'm guessing that what you mean by "may reject" is the same as what
>>> I mean by "may choose not to accept". I'd like to know if you think
>>> that's right, or if you think there is some difference between the
>>> two. (My intention is that the two phrases have the same meaning.)
>>>
>>> Does the above adequately address the question you want answered?
>>
>> I'm not sure. As I recall, I gave up on trying to understand what
>> you think "accept" means.
>>
>> N1570 5.1.2.3p6:
[CORRECTION: 3p4]
>>
>> A program that is correct in all other aspects, operating on
>> correct data, containing unspecified behavior shall be a
>> correct program and act in accordance with 5.1.2.3.
>>
>> Does that not apply to the program above? How can it do so if it's
>> rejected (or not "accepted")?
>>
>> The same paragraph says that "A *conforming hosted implementation*
>> shall accept any strictly conforming program". Are you reading
>> that as implying that *only* strictly conforming programs must be
>> accepted?
>>
>> As a practical matter, an implementation that accepts *only*
>> strictly conforming programs would be very nearly useless. I
>> don't see anything in the standard that says a program can be
>> rejected purely because it's not strictly conforming, and I don't
>> believe that was the intent.
>
> My understanding of the C standard is that 'shall accept' is
> meant in the sense of 'shall use its best efforts to complete
> translation phases 1 through 8 successfully and produce an
> executable'.
That sounds reasonable. I wish the standard actually defined "accept".
> Where you say "5.1.2.3p6:" I expect you mean "4p3".
Yes.
> Where you say "the same paragraph" I expect you mean "4p6".
Yes.
> The word "reject" does not appear in the C standard. In my own
> writing I am trying henceforth to use "accept" exclusively and
> not use "reject". For the safe of discussion I can take "reject"
> to mean the logical complement of "accept", which is to say a
> program is either accepted or rejected, never both and never
> neither. Does that last sentence match your own usage?
Yes, "reject" means "not accept". There might be some nuance that that
definition misses, so I'll try to avoid using the word "reject" in this
discussion.
> The C standard has only one place where a statement is made about
> accepting a program, saying in 4p6 that implementations shall
> accept any strictly conforming program; no other paragraph in the
> standard mentions accepting a program. Given that, it's hard for
> me to understand how someone could read the standard as saying
> anything other than that a program must be accepted if it is
> strictly conforming, but if the program is not strictly conforming
> then there is no requirement that it be accepted. In short form, a
> program must be accepted if and only if it is strictly conforming.
> Does that summary mean something different than your phrase "*only*
> strictly conforming programs must be accepted"?. My understanding
> of the C standard is that strictly conforming programs must be
> accepted, but implementations are not required to accept any
> program that is not strictly conforming.
Certainly a conforming implementation must accept any strictly
conforming program (insert handwaving about capacity limits).
I can understand how one might read that requirement as implying that an
implementation need not accept any program that is not strictly
conforming. I don't read it that way.
> In response to your question about 4p3, the short answer is that
> any non-strictly-conforming program that an implementation chooses
> not to accept is not correct in all other aspects, so 4p3 does not
> apply. If you want to talk about that further we should split that
> off into a separate thread, because 4p3 has nothing to do with
> program acceptance.
I say it does. Under 4p3, the above program (that prints the value of
INT_MAX) is a "correct program", so it must "act in accordance with
5.1.2.3". It cannot do so unless it is first accepted.
You're saying that the correctness of a program can depend on whether an
implementation chooses to accept it. I disagree.
An implementation that does not accept the above program is not
conforming because the implementation violates 4p3.
[...]
--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Medtronic
void Void(void) { Void(); } /* The recursive call of the void */
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
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Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-08 08:04 -0800
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Re: ustent on that. Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-10 01:20 +0000
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Re: Is C ready to become a safer language? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2024-02-09 13:01 +0000
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-09 15:08 +0100
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Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-09 08:14 +0100
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-09 08:28 -0800
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Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-10 23:22 -0800
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Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-11 23:48 -0800
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Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-10 20:22 +0000
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Re: Is C ready to become a safer language? vallor <vallor@cultnix.org> - 2024-02-11 00:40 +0000
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-11 01:06 +0000
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Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-10 19:54 -0800
Re: Is C ready to become a safer language? vallor <vallor@cultnix.org> - 2024-02-13 06:22 +0000
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Re: Is C ready to become a safer language? Richard Harnden <richard.nospam@gmail.invalid> - 2024-02-11 11:31 +0000
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Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-11 14:17 +0000
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