Can I use fseek to control file size?

[deko]

I'm trying to control the size of a log file. When it gets more than 5k
oversize, I attempt to trim it thusly:

$fcap = intval(($dval * 0.0108))*1024; // what it should be
$fsize = filesize($file) ; // what it is
$oversize = $fsize - $fcap;

if ( $oversize > 5120 ) // 5k oversize
{
$fp = fopen($file,"r+ ");
fseek($fp, -$fcap, SEEK_END);
$redux = fread($fp, $fsize);
$fp = fopen($file,"w" );
fwrite($fp, $redux);
}

The problem is the file is getting wiped out - reduced to 0k

Doesn't the fseek statement say "move the pointer to the end of the file,
then back up by the amount of $fcap" ? Then, data from the pointer down is
read into $redux, and $redux overwrites $file ?

Am I missing something? Why is my log file getting wiped out?

[Chris]

Re: Can I use fseek to control file size?

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deko wrote:
[color=blue]
> I'm trying to control the size of a log file. When it gets more
> than 5k oversize, I attempt to trim it thusly:
>
> $fcap = intval(($dval * 0.0108))*1024; // what it should be
> $fsize = filesize($file) ; // what it is
> $oversize = $fsize - $fcap;
>
> if ( $oversize > 5120 ) // 5k oversize
> {
> $fp = fopen($file,"r+ ");
> fseek($fp, -$fcap, SEEK_END);
> $redux = fread($fp, $fsize);
> $fp = fopen($file,"w" );
> fwrite($fp, $redux);
> }
>
> The problem is the file is getting wiped out - reduced to 0k
>
> Doesn't the fseek statement say "move the pointer to the end of the
> file,
> then back up by the amount of $fcap" ? Then, data from the pointer
> down is read into $redux, and $redux overwrites $file ?
>
> Am I missing something? Why is my log file getting wiped out?[/color]

Hi,
First, the first fopen() should probably use mode "r".

Second, you're not closing the file after the first use, so this might
screw things up. Put an fclose($fp); after the fread() line.

Third, shouldn't the fread() line be reading $fcap bytes, not $fsize
bytes? Reading $fsize bytes means trying to go beyond EOF (which
according to the documentation isn't a problem), while reading $fcap
bytes means you get *exactly* what you want.

If nothing works, try some error checking on every single line inside
the loop: they *all* return values.

Chris
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[deko]

Re: Can I use fseek to control file size?

> First, the first fopen() should probably use mode "r".

I think I remember trying this but it did not work for some reason. I'll
try it again.
[color=blue]
> Second, you're not closing the file after the first use, so this might
> screw things up. Put an fclose($fp); after the fread() line.[/color]

That part of the code was omitted.
[color=blue]
> Third, shouldn't the fread() line be reading $fcap bytes, not $fsize
> bytes? Reading $fsize bytes means trying to go beyond EOF (which
> according to the documentation isn't a problem), while reading $fcap
> bytes means you get *exactly* what you want.[/color]

perhaps...
[color=blue]
> If nothing works, try some error checking on every single line inside
> the loop: they *all* return values.[/color]

Actually, I got it working - the issue was a file lock routine that was not
part of my post.

Thanks for the reply.

[Drazen Gemic]

Re: Can I use fseek to control file size?

On Thu, 09 Sep 2004 04:09:57 +0000, deko wrote:
[color=blue]
> Actually, I got it working - the issue was a file lock routine that was not
> part of my post.[/color]

I think that it is a good idea to call 'clearstatcache ' before 'filesize'.

DG