[PATCH] Various pages: SYNOPSIS: Use VLA syntax in function parameters

[Alejandro Colomar]

Hi Martin,

On 11/13/22 14:19, Alejandro Colomar wrote:
>> But there are not only syntactical problems, because
>> also the type of the parameter might become relevant
>> and then you can get circular dependencies:
>>
>> void foo(char (*a)[sizeof *.b], char (*b)[sizeof *.a]);
> 
> This seems to be a difficult stone in the road.
> 
>>
>> I am not sure what would the best way to fix it. One
>> could specifiy that parameters referred to by
>> the .identifer syntax must of some integer type and
>> that the sub-expression .identifer is always
>> converted to a 'size_t'.
> 
> That makes sense, but then overnight some quite useful thing came to my mind 
> that would not be possible with this limitation:
> 
> 
> <https://software.codidact.com/posts/285946>
> 
> char *
> stpecpy(char dst[.end - .dst], char *src, char end[1])
> {
>      for (/* void */; dst <= end; dst++) {
>          *dst = *src++;
>          if (*dst == '\0')
>              return dst;
>      }
>      /* Truncation detected */
>      *end = '\0';
> 
> #if !defined(NDEBUG)
>      /* Consume the rest of the input string. */
>      while (*src++) {};
> #endif
> 
>      return end + 1;
> }

And I forgot to say it:  Default promotions rank high (probably the highest) in 
my list of most hated features^Wbugs in C.  I wouldn't convert it to size_t, but 
rather follow normal promotion rules.

Since you can use anything between INTMAX_MIN and UINTMAX_MAX for accessing an 
array (which took me some time to understand), I'd also allow the same here. 
So, the type of the expression between [] could perfectly be signed or unsigned.

So, you could use size_t for very high indices, or e.g. ptrdiff_t if you want to 
allow negative numbers.  In the function above, since dst can be a pointer to 
one-past-the-end (it represents a previous truncation; that's why the test 
dst<=end), forcing a size_t conversion would disallow that syntax.

Cheers,

Alex

-- 
<http://www.alejandro-colomar.es/>
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