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]

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deko wrote:

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?

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]

> 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.

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.
That part of the code was omitted.
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.
perhaps...
If nothing works, try some error checking on every single line inside
the loop: they *all* return values.

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]

On Thu, 09 Sep 2004 04:09:57 +0000, deko wrote:

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

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

DG