php简单防刷计数器

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<?php
require_once('config.php');
function counter()
{
session_start();
$sql="select counter from counter";
$result=@mysql_query($sql);
if(!empty($result))
{
$row=mysql_fetch_array($result);
$counter=++$row[counter];
if(!$_SESSION['counter'])
{
$query="update counter set counter=$counter";
$result=@mysql_query($query);
if($result)
{
$_SESSION['counter']=true;
}
}
$counter_len=strlen($counter);
for($i=0;$i<$counter_len;$i++)
{
$number=substr($counter,$i,1);
if(isset($number))
{
echo "<img src='image/".$number.".gif'>";
}
}
}
}
?>