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From: Thiago Adams <thiago.adams@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: on allowing "int a" definition everywhere
Date: Wed, 21 Aug 2024 10:01:12 -0300
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On 21/08/2024 09:34, Bart wrote:
> 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?

Compile time. f is not visible outside.
> 
> 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
>   }
> 

For this type of error you need my static analyzer. (cake) :D

http://thradams.com/cake/playground.html?code=I3ByYWdtYSBzYWZldHkgZW5hYmxlCiNpbmNsdWRlIDxzdGRpby5oPgppbnQgbWFpbigpCnsKICAgRklMRSogX093bmVyIF9PcHQgZjsKICAgaWYgKCBmID0gZm9wZW4oImZpbGUudHh0IiwgInIiKSkKICAgewogICAgY2hhciBhW109ImFiIjsKICAgIGZjbG9zZShmKTsgICAgIAogICAgZndyaXRlKGEsIDEsIDIsIGYpOyAgICAgCiAgIH0KfQo%3D&to=-1&options=


> 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.

It is something optional to use.

> 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.
> 
>