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From: Bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: Re: on allowing "int a" definition everywhere
Date: Thu, 22 Aug 2024 11:00:28 +0100
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On 22/08/2024 09:40, Blue-Maned_Hawk wrote:
> Thiago Adams wrote:
> 
>> On 21/08/2024 01:42, Blue-Maned_Hawk wrote:
>>> Thiago Adams wrote:
>>>
>>>> initializer inside if is already in C++, and it will probably be on
>>>> C2Y.
>>> If it's for consistency with how for loops permit declarations, i would
>>> _much_  prefer that they just outlaw that to induce consistency.
>>>
>>> (Really, i'd ideally want things to just stay as they are, since
>>> declarations in for loops are simply too useful for macros.)
>>
>> I like the ability to declare things inside if.
>>
>> if (FILE* f = fopen("file.txt", "r"))
>> {
>>     /*...*/ fclose(f);
>> }
>>
>> Because it makes the scope of f, associated with the pointed object
>> lifetime.
>>
>> For instance, if you try to use f
>>
>> if (FILE* f = fopen("file.txt", "r"))
>> {
>>     /*...*/ fclose(f);
>> }
>> fwrite(f, ..) ;// ERROR
> 
> You can already do that in C23:
> 
> if (…) {
> 	FILE * f = fopen("file.txt", "r");
> 	/* … */
> 	fclose(f);
> }
> fwrite(f, …);  /* Some kind of error happens. */
> 
> Or, if you need it to exist before the controlling expression:
> 
> for (bool x = true; x; x = false)  for (FILE * f = fopen("file.txt", "r");
> x; x = false)  if (…) {
> 	/* … */
> 	fclose(f);
> }
> fwrite(f, …);
> 

I wonder, if I laid it out it properly:

     for (bool x = true; x; x = false)
         for (FILE * f = fopen("file.txt", "r"); x; x = false)
             if (…) {
                 /* … */
                 fclose(f);
             }
     fwrite(f, …);

Nope; I still haven't the faintest idea what this is supposed to do. I 
suspect that it doesn't actually run or need those two nested loops.

I assume the (...) tests the value of 'f'? If so then perhaps this is a 
shorter way of expressing the same thing:

     {
         FILE * f = fopen("file.txt", "r");
         if (f) {
             /* … */
             fclose(f);
         }
     }
     fwrite(f, …);