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From: Andrey Tarasevich <noone@noone.net>
Newsgroups: comp.lang.c
Subject: Re: Buffer contents well-defined after fgets() reaches EOF ?
Date: Sat, 8 Feb 2025 23:12:44 -0800
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On Sat 2/8/2025 10:23 PM, Andrey Tarasevich wrote:
> 
> Note also that `fgets` is not permitted to assume that the limit value 
> (the second parameter) correctly describes the accessible size of the 
> buffer. E.g. for this reason it is not permitted to zero-out the buffer 
> before reading. For example, this code is valid and has defined behavior
> 
>    char buffer[10];
>    fgets(buffer, 1000, f);
> 
> provided the current line of the file fits into `char[10]`. I.e. even 
> though we "lied" to `fgets` about the limit, it is still required to 
> work correctly if the actual data fits into the actual buffer.

.... and this part of specification effectively guarantees, that any 
[tail] portion of the buffer not overwritten by the characters obtained 
from file, will remain unchanged. If `fgets` reads 5 characters from the 
file, only first 6 characters of the buffer will be overwritten, while 
the rest is guaranteed to remain untouched. If `fgets` reads nothing 
(instant end-of-file), the entire buffer remains untouched.

-- 
Best regards,
Andrey