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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Abstract Syntax Tree for C programs
Date: Wed, 05 Jun 2019 12:12:19 -0700
Organization: None to speak of
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David Brown <david.brown@hesbynett.no> writes:
> On 04/06/2019 23:41, Keith Thompson wrote:
>> David Brown <david.brown@hesbynett.no> writes:
>>> On 04/06/2019 12:24, Bart wrote:
>> [...]
>>>>  int main (void) {
>>>>     fn(1,2,3,4);
>>>>     fn("hello world");
>>>>  }
>>>>
>>>> There are no declarations of 'fn' visible; should this code pass or
>>>> fail? Apparently gcc passes this unless I do:
>>>
>>> Sure, the code passes - because it has specific known behaviour, in an
>>> older version of C.
>> 
>> No, it has undefined behavior in every version of C that has the concept
>> of undefined behavior.  The function fn is presumably defined somewhere.
>> That definition is consistent with at most one of those calls.  It is
>> not possible to write a definition of fn for which both calls have
>> behavior that is defined by the standard.
>> 
>> (Of course an implementation could define the behavior.)
>
> You are assuming that the implementation of "fn" is written in C.

I am not.  If the implementation of fn is not written in C, then its
behavior is not defined by the C standard.  That's undefined behavior.

[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */