Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.c > #382206
| From | Keith Thompson <Keith.S.Thompson+u@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Is C ready to become a safer language? |
| Date | 2024-02-09 08:48 -0800 |
| Organization | None to speak of |
| Message-ID | <87v86xeg7q.fsf@nosuchdomain.example.com> (permalink) |
| References | (2 earlier) <uq22na$1sppb$1@dont-email.me> <87bk8rgcy0.fsf@nosuchdomain.example.com> <uq2um0$21dgh$1@dont-email.me> <uq4jm5$2h9hc$2@dont-email.me> <uq4l7p$2hik2$1@dont-email.me> |
Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
> On 09/02/2024 07:19, David Brown wrote:
>> On 08/02/2024 17:14, Malcolm McLean wrote:
>>> On 08/02/2024 16:04, Keith Thompson wrote:
>>>> In a freestanding implementation, main() *might* be just another
>>>> function. In that case a compiler can't prove that the code will be
>>>> invoked.
>>>>
>>> Well sometimes it can. The boot routine or program entry point is
>>> by defintion always invoked, and you can generally prove that at
>>> least some code is always reached from that. However it is the
>>> halting problem, and you can never prove for all cases, even if the
>>> code must be reached or not reached regardless of runtime inputs.
>>>
>> It is not "the halting problem". What you are trying to say, is
>> that it is undecidable or not a computable problem in the general
>> case.
>>
> The "is this code reached?" problem is the halting problem with the
> trivial and unimportant difference that the code in question does not
> have to be "exit()".
Your earlier statement that "it is the halting problem" is at best
questionable, partly because it's not clear what "it" refers to in that
statement.
The issue is not whether we understand what the halting problem is.
The issue is that it's not relevant in this context.
We were discussing whether a compiler can reject a program that has
undefined behavior. It clearly can *if* the undefined behavior will
occur in every execution of the program (for all inputs if the program
has inputs).
If a program includes the expression 1/0, evaluation that expression has
undefined behavior, but there is no undefined behavior if that code is
never reached and the expression is not evaluated.
Determining, for all programs containing the expression 1/0, whether
that expression will be evaluated is (probably) more or less equivalent
to the halting problem, which means that no compiler can perfectly
determine whether it's allowed to reject such programs.
But the halting program is irrelevant because *compilers are not
required to do that*. Most compilers do *some* flow analysis, and can
determine *in some cases* whether a given expression will always,
sometimes, or never be evaluated, but they cannot, do not, and are not
required to do a perfect job. They are not required to do any such
analysis at all. A conforming compiler can issue a non-fatal warning
whenever it sees a division by a constant 0, not caring whether it can
be reached -- or it can ignore the issue altogether (except that it must
detect it if it occurs in a context that requires a constant
expression).
The example was one in which it's trivially provable that the expression
1/0 will be evaluated whenever the program is executed (assuming a
hosted implementation).
And if you and David want to argue about Oxford English degrees, I urge
*both of you* to do it elsewhere. David, you don't have to respond to
everything.
--
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
Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 01:01 -0300
Re: Is C ready to become a safer language? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-08 04:40 +0000
Re: Is C ready to become a safer language? Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-08 05:00 +0000
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 09:20 -0300
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-08 17:02 +0000
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 14:17 -0300
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 14:19 -0300
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-08 09:57 -0800
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-08 09:45 -0800
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 14:56 -0300
Re: Is C ready to become a safer language? Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-08 04:58 +0000
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-07 21:33 -0800
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-07 20:59 -0800
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-08 09:17 +0100
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 09:48 -0300
Re: Is C ready to become a safer language? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-08 14:42 +0000
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-08 16:25 +0100
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 13:15 -0300
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-08 21:42 +0100
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-08 08:04 -0800
Re: Is C ready to become a safer language? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-08 16:14 +0000
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-08 08:32 -0800
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-09 08:19 +0100
Re: Is C ready to become a safer language? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-09 07:46 +0000
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-09 09:33 +0100
Re: Is C ready to become a safer language? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-09 10:03 +0000
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-09 11:17 +0100
Re: Is C ready to become a safer language? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2024-02-09 10:24 +0000
Re: Is C ready to become a safer language? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-09 11:24 +0000
Re: Is C ready to become a safer language? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2024-02-09 13:28 +0000
Re: Is C ready to become a safer language? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-09 14:04 +0000
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-09 15:03 +0100
ustent on that. Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-09 16:01 +0000
Re: ustent on that. David Brown <david.brown@hesbynett.no> - 2024-02-09 18:00 +0100
Re: ustent on that. Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-10 01:20 +0000
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-09 12:45 +0000
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
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-09 08:48 -0800
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
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-09 20:15 +0100
Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-10 02:28 -0800
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-10 16:15 -0800
Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-10 23:22 -0800
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-11 00:12 -0800
Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-11 23:48 -0800
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-18 15:28 -0800
Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-03-23 10:35 -0700
Re: Is C ready to become a safer language? Richard Kettlewell <invalid@invalid.invalid> - 2024-02-08 15:37 +0000
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-08 13:25 -0300
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-08 16:30 +0000
Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-09 17:59 -0800
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-10 20:22 +0000
Re: Is C ready to become a safer language? Richard Harnden <richard.nospam@gmail.invalid> - 2024-02-10 21:30 +0000
Re: Is C ready to become a safer language? Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-10 21:49 +0000
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-10 20:44 -0300
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-11 13:06 +0100
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-11 15:43 -0300
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-11 13:33 -0800
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-12 11:32 +0100
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-11 00:02 +0000
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-10 17:39 -0800
Re: Is C ready to become a safer language? Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-11 02:46 +0000
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-11 12:24 +0000
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-11 15:06 +0100
Re: Is C ready to become a safer language? Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-11 18:32 +0000
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-11 13:15 +0100
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-10 16:31 -0800
Re: Is C ready to become a safer language? Thiago Adams <thiago.adams@gmail.com> - 2024-02-11 15:57 -0300
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-11 13:47 -0800
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
Re: Is C ready to become a safer language? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-10 17:51 -0800
Re: Is C ready to become a safer language? David Brown <david.brown@hesbynett.no> - 2024-02-11 13:27 +0100
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
Re: Is C ready to become a safer language? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-11 11:01 +0000
Re: Is C ready to become a safer language? Richard Harnden <richard.nospam@gmail.invalid> - 2024-02-11 11:31 +0000
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-11 12:38 +0000
Re: Is C ready to become a safer language? Richard Harnden <richard.nospam@gmail.invalid> - 2024-02-11 13:23 +0000
Re: Is C ready to become a safer language? bart <bc@freeuk.com> - 2024-02-11 14:17 +0000
Re: Is C ready to become a safer language? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-02-10 22:21 -0800
csiph-web