Re: bart again (UCX64)

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: bart again (UCX64)
Date	2023-09-13 12:43 +0200
Organization	A noiseless patient Spider
Message-ID	<uds3o7$23bp5$1@dont-email.me> (permalink)
References	(11 earlier) <DD0MM.39423$jJK6.35686@fx14.iad> <647ac7a4-fb14-4072-b65f-5b20290a4b7bn@googlegroups.com> <KN1MM.6185$Q73f.3452@fx48.iad> <udqdr6$1milh$2@dont-email.me> <16d2ead0-48b5-4b73-9bec-03073d98d9d3n@googlegroups.com>

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On 13/09/2023 11:07, Malcolm McLean wrote:
> On Tuesday, 12 September 2023 at 20:23:32 UTC+1, David Brown wrote:
>> On 12/09/2023 20:07, Scott Lurndal wrote:
>>
>>> I would assume that the designer would anticipate such a
>>> condition and the function that obtains the sensor reading
>>> would indicate a failure condition that would be handled
>>> according to the design specification. There is no need
>>> to use a NaN for that, there are dozens of alternatives.
>> A common standard for sensors is to provide a 4 to 20 mA output for the
>> signal. That leaves 0 mA to indicate disconnected, and a value of
>> perhaps 1 mA to indicate a fault. That is, of course, at electrical
>> interface, but the same principles can be used in software, such as a
>> value of 0 to 1000 for valid readings and -1 for invalid readings.
>>
> I don't do embedded programming (I have dabbled, but nothing serious).
> But in most software engineering contexts, you would want to abstract
> away the result of a call to readsensors() from the physical details of
> how the sensors work.

Agreed.  But the type of abstraction is going to be very variable 
depending on the kind of code, and the part of the code you are working 
on at the time.  A double might be a reasonable choice for a sensor 
value in simple cases where you know everything is fine - it would not 
be a suitable type for tracking failures or possible uncertainties in a 
measurement.

>>
>> And as you say, there are /many/ ways to do this. In C++, I might have
>> the readsensors() function return a std::optional<oxygen_ml_per_sec_t>
>> to make it easy to see when there is a valid value. In C, it would
>> perhaps be a struct with a bool "valid" flag. It's also common to have
>> such functions take a pointer-to-result parameter and return a status flag.
>>
>> But I would not be returning either a double or an integer type - it
>> would be a specific type, whose name included the units, to make it as
>> difficult as possible to make a mistake.
>>
> There's no way of attaching units to C variables, but one way is to use
> types. 

You contradict yourself.  There /is/ a way of attaching units to C 
variables - you use types, as I said above.

You can also use good naming practices.  Having a double called 
"oxygen_ml_per_sec", rather than "oxygen_rate", attaches a unit to the 
variable.  The compiler can't check the units by name, but at least 
human readers can do so.

> But in large programs that can cause problems because the types
> will usually only support the four rules of arithemetic. 

You are jumbling concepts again, and imagining things.  (Again, I would 
encourage you to use Wikipedia whenever you want to use the word "the". 
Look up "The Four Rules of Arithmetic" on Wikipedia - there is no such 
thing.  It's all in your mind, and it really does not help the 
conversation at all.)

> So the usual solution
> is to use SI units. So a flow would be litres per second, not ml per second.
> (So you do need a decent range and prescision, because the values might
> very quite high or quite low in relation to the units).

Doubles in SI units can be a good choice in many cases, yes.  But you 
can do better in C - and if the code is safety-critical, such as this 
case, you /should/ do better.  Wrap the value in a struct, then the type 
safety rules of C will stop you making mistakes.  The types are more 
awkward to use, of course - you have to use member access or specific 
functions to access the actual values or do arithmetic on them.  That is 
a price worth paying for safety.  (Alternatively, you use a language 
that has better support for such things, like C++ or Ada.)

The bigger the program, the more important this kind of thing is - you 
do not skimp on appropriate levels of safety just because the code base 
is large.

Thread

Re: bart again (UCX64) candycane@f172.n1.z21.fsxnet (candycane) - 2023-09-06 19:53 +1300
  Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-07 12:00 -0700
    Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 16:33 -0700
      Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-07 20:55 -0700
        Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 22:16 -0700
          Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-08 07:09 +0000
            Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 10:10 +0200
              Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 01:30 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 11:26 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-08 10:44 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 13:26 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:57 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-09 18:36 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 18:19 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 13:28 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-10 13:20 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 15:19 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-10 16:07 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 18:33 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-10 15:44 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 18:36 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:48 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-09 19:04 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 02:47 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 16:03 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 16:06 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-09 01:52 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 18:16 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-09 21:31 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 12:03 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-10 21:36 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 08:51 +0200
                Re: bart again (UCX64) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-09-10 23:59 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 01:01 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 11:17 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 03:16 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 14:58 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 06:35 -0700
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-11 14:13 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 16:24 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 14:55 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 16:42 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-11 14:29 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 11:25 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 03:59 -0700
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-11 13:57 +0000
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 09:52 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 16:07 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-11 16:26 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 16:47 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 19:14 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-11 22:30 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 23:07 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-11 23:31 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 09:18 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 03:01 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 10:08 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-11 23:18 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 23:37 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 15:46 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-11 23:40 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 01:50 +0100
                Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-11 17:59 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-12 01:03 +0000
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 02:39 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 11:28 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 14:49 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 15:18 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 03:58 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 02:25 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 16:17 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 17:28 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 21:07 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 03:01 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 09:38 +0200
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 10:00 +0200
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-19 05:22 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-19 14:29 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 13:35 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 20:48 +0100
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-19 05:53 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 09:33 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-12 16:48 +0000
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 10:57 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-12 18:07 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 21:23 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 02:07 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 12:43 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 04:04 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 14:07 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 01:47 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 13:02 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 04:45 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 14:36 +0200
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-13 13:43 +0000
                Re: bart again (UCX64) James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-09-13 11:10 -0400
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-13 17:12 +0000
                [meta] spam in thread Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 11:22 -0700
                Re: [meta] spam in thread Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-13 18:40 +0000
                Re: [meta] spam in thread Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 11:48 -0700
                Re: [meta] spam in thread David Brown <david.brown@hesbynett.no> - 2023-09-13 21:01 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 19:58 +0100
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-18 12:36 -0700
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-18 13:40 -0700
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-20 19:43 -0700
                Re: bart again (UCX64) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-09-20 20:14 -0700
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-20 22:10 -0700
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-01 11:03 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 07:39 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-13 15:18 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 18:39 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 15:44 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 08:42 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 22:35 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 18:49 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 15:40 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 03:36 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 12:58 +0200
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 12:49 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 12:52 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 05:22 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 15:05 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 02:17 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 14:44 +0200
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-08 14:36 +0000
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:50 +0000
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-09 15:40 +0000
          Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 09:57 +0200
          Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-09 10:23 -0700

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