Re: Whaddaya think?

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);
}

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

Janis