Re: diagnosing C errors, was Alternative C compilers on x86_64 Linux?

On 2016-09-09, BartC <bc@freeuk.com> wrote:
> On 06/09/2016 01:26, alexfrunews@gmail.com wrote:
>> On Sunday, September 4, 2016 at 3:56:56 PM UTC-7, jacobnavia wrote:
>>> Why should they care? If you write duplicate switch cases its not their
>>> fault, its yours.
>>
>> It is a constraint violation, and a trivial one, that the compiler
>> must identify and report instead of silently producing code that is
>> broken or appears to work by chance.
>
> This is C. There are already plenty of things that it lets through that
> are probably errors, and which are likely to crash the program.


That's true. The major real-world consequence of not producing
an ISO-C required diagnostic is that the code will fail to compile
on compilers other than the one with which it was developed.


Though you may have some dead code in a switch statement, and that could
be a bug, on the other hand, you test the code. It's not a bug if there
is no external test case which reproduces an issue.


And that brings us to Aharon's original point about looking for
a compiler that can be used for *development*. A compiler used for
development should have excellent diagnostics, which helps make the code
cleanly portable to other compilers.


> By contrast, an inadvertent duplicate case label is a 'soft' error; the
> program just won't give the expected results.


Or, as I argue about, there might in fact be no bug: the correct fix
might in fact be just to remove the duplicate label and all the code
under it.


Some ISO C required diagnostics do help uncover real errors, which
helps, in spite of the C language having lots of pitfalls and holes.


Imagine if you could assign any scalar type to any other without needing
a cast, and with no diagnostic: double x = "abc", and so on.
Or call functions without any parameter checking.


The type checking in C does a lot for improving the reliability of C
programs, even though it falls far short of repairing all the holes
and pitfalls.

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