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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: bugprone-switch-missing-default-case
Date: Thu, 23 Oct 2025 19:13:31 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
> pozz <pozzugno@gmail.com> writes:
>> Il 22/10/2025 21:41, Keith Thompson ha scritto:
> [...]
>>> That document is poorly written.  The phrase "without any defined
>>> behavior" strongly implies that the behavior is undefined, which is
>>> simply wrong.
>>> It says:
>>>      When a switch statement lacks a default case, if a value is
>>>      encountered that does not match any of the specified cases, the
>>>      program will continue execution without any defined behavior or
>>>      handling.
>>> It would be more accurate to say:
>>>      When a switch statement lacks a default case, if a value is
>>>      encountered that does not match any of the specified cases, the
>>>      switch statement will do nothing and the program will continue
>>>      execution without handling the value.
>>> A warning might be warranted, but the behavior is well defined.
>>
>> It is exactly what i wanted to read. Thanks for the explanation.
>>
>>> Note that the documentation is for the add-on tool clang-tidy, not for
>>> the clang compiler.
>>
>> Sure
>>
>>
>>> I've submitted a bug report :
>>> https://github.com/llvm/llvm-project/issues/164699
>
> My fix for this has been accepted into the llvm-project git repo.
>
> The web page
> https://clang.llvm.org/extra/clang-tidy/checks/bugprone/switch-missing-default-case.html
> has not yet been updated (not surprisingly).

And now it's been updated:

    Switch statements without a default case can lead to unexpected
    behavior and incomplete handling of all possible cases. When a
    switch statement lacks a default case, if a value is encountered
    that does not match any of the specified cases, the switch
    statement will do nothing and the program will continue execution
    without handling the value.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */