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From: Michael S <already5chosen@yahoo.com>
Newsgroups: comp.lang.c
Subject: Re: Whaddaya think?
Date: Sun, 16 Jun 2024 11:11:34 +0300
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On Sun, 16 Jun 2024 07:41:38 +0200
Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:

> On 16.06.2024 07:21, Keith Thompson wrote:
> > Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:  
> >> On 16.06.2024 05:41, Janis Papanagnou wrote:  
> >>> On 16.06.2024 05:26, Lawrence D'Oliveiro wrote:  
> >>>> On Sun, 16 Jun 2024 01:56:49 +0300, Michael S wrote:
> >>>>  
> >>>>> If you want to preserve you sanity, never use fscanf().  
> >>>>
> >>>> Quoth the man page
> >>>> <https://manpages.debian.org/3/scanf.3.en.html>:
> >>>>
> >>>>     It is very difficult to use these functions correctly, and
> >>>> it is preferable to read entire lines with fgets(3) or
> >>>> getline(3) and parse them later with sscanf(3) or more
> >>>> specialized functions such as strtol(3).  
> >>>
> >>> This would be also my first impulse, but you'd have to know
> >>> _in advance_ how long the data stream would be; the function
> >>> requires an existing buffer. So you'd anyway need a stepwise
> >>> input. [...]  
> >>
> >> Would it be sensible to have a malloc()'ed buffer used for the
> >> first fgets() and then subsequent fgets() work on the realloc()'ed
> >> part? I suppose the previously set data in the malloc area would
> >> be retained so that there's no re-composition of cut numbers
> >> necessary?  
> > 
> > Sure.  "The contents of the new object shall be the same as that of
> > the old object prior to deallocation, up to the lesser of the new
> > and old sizes."
> > 
> > Keep in mind that you can't call realloc() on a non-null pointer
> > that wasn't allocated by an allocation function.  
> 
> Thanks. - I've just tried it with this ad hoc test code
> 
> #include <stdlib.h>
> #include <stdio.h>
> 
> void main (int argc, char * argv[])
> {
>     int chunk = 10;
>     int bufsize = chunk+1;
>     char * buf = malloc(bufsize);
>     char * anchor = buf;
>     while (fgets(buf, chunk+1, stdin) != NULL)
>         if (realloc(anchor, bufsize += chunk) != NULL)
>             buf += chunk;
>     puts(anchor);
> }
> 

Not sure what this code is supposed to do.
However it looks unlikely that it does what you meant for it to do.
I recommend to read the [f*****g] manual.
https://cplusplus.com/reference/cstdio/fgets/
https://cplusplus.com/reference/cstdlib/realloc/

> I wonder whether it can be simplified by making malloc() obsolete
> and using realloc() in a redesigned loop.
> 
> Janis
>