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From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: "undefined behavior"?
Date: Fri, 14 Jun 2024 00:41:08 +0100
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On 13/06/2024 22:47, Keith Thompson wrote:
> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>> On 13/06/2024 01:33, Keith Thompson wrote:
>>> printf is a variadic function, so the types of the arguments after
>>> the format string are not specified in its declaration.  The printf
>>> function has to *assume* that arguments have the types specified
>>> by the format string.  This:
>>>       printf("%d\n", foo);
>>> (probably) has undefined behavior if foo is of type size_t.
>>>
>> And isn't that a nightmare?
> 
> Not at all.  Compilers commonly diagnose mismatches when the format
> string is a string literal, as it most commonly is.  The format
> specifier for size_t is "%zu", since C99.
> 
>>> There is no implicit conversion to the expected type.  Note that
>>> the format string doesn't have to be a string literal, so it's
>>> not always even possible for the compiler to check the types.
>>> Variadic functions give you a lot of flexibility at the cost of
>>> making some type errors difficult to detect.
>>> (I wrote "probably" because size_t *might* be a typedef for unsigned
>>> int, and there are special rules about arguments of corresponding
>>> signed and unsigned types.)
>>
>> We just can't have size_t variables swilling around in prgrams for
>> these reasons.
> 
> We can and do.
> 
And this is how things break.

Now, running a third party editor under your control so that user can 
edit an text and return control and the edited text back to you when he 
exits the editor. Yes, I understand that this is a difficult thing to 
do, the software engineeering isn't consistent, and theway you have to 
do it may change from one version of C to another.
But printing out a variable which holds the length of a string? And 
something so basic breaks from one version of C to the next? We should 
ahave no tolerance for that at all.
-- 
Check out my hobby project.
http://malcolmmclean.github.io/babyxrc