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From: Bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: Re: on allowing "int a" definition everywhere
Date: Wed, 21 Aug 2024 13:34:51 +0100
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On 21/08/2024 12:17, 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

Run-time or compile-time error?

It won't be a compile-time error if there is another 'f' visible in that 
outer scope.

And it won't be one here either:

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

Meanwhile, I'd have a serious problem with the extra clutter this 
causes. Since you are not reporting an fopen failure, I'd write this as:

   FILE* f;

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

However I'd be more likely check for failure first.

Since I did a recent survery where, on a average, functions only had 3 
local variables (in a selection of apps), I've been even more sceptical 
of block-scoped variables.