Re: Buffer contents well-defined after fgets() reaches EOF ?

On 10.02.2025 02:32, Ben Bacarisse wrote:

Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
 

To get the last line of a text file I'm using
>
    char buf[BUFSIZ];
    while (fgets (buf, BUFSIZ, fd) != NULL)
        ;   // read to last line
>
If the end of the file is reached my test shows that the previous
contents of 'buf' are still existing (not cleared or overwritten).

 
Something that has not yet come up (as far as I can see) is that you
might need to handle an empty file.  In such a case, nothing gets
written and fgets returns NULL right away.  Processing buf in this
situation is then undefined.

I haven't considered that at all because my context is very specific;
it's just three text lines (a comment line, an empty separator line,
and a line with the payload data that I'm interested in). If there's
a file it will have exactly these three lines (and all correctly and
consistently terminated).

 
One way to handle this is to put into buf something that can't get read
by fgets.  Two newlines is a good candidate:
 
  char buf[BUFSIZE] = "\n\n";
 
You can then test for that if need be, though of course it all depends
on what your application is doing.

Thanks for pointing it out and for the suggestion.

Janis