pdo 链接sqlserver

<?php
header("Content-type: text/html; charset=utf-8");
if(PATH_SEPARATOR==':')
    echo '本机操作系统是：Linux<br>';
else
    echo '本机操作系统是：Windows<br>';
 
try {
    //服务器
    $host = "127.0.0.1";
    $port = '1433';
    $dbname = "oblog46";
    $username = "sa";
    $pw = "123456";
    $dbh = null;
 
    if(PATH_SEPARATOR==':'){
        $dbh = new PDO ("dblib:host=$host:$port;dbname=$dbname","$username","$pw");
    }else{
        $dbh = new PDO("sqlsrv:Server=$host,$port;Database=$dbname",$username,$pw);
    }
} catch (PDOException $e) {
    echo "Failed to get DB handle: " . $e->getMessage() . "\n";
    exit;
}
 
$stmt = $dbh->prepare("SELECT top 3 * FROM oblog_log");
$stmt->execute();
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    echo "<pre>";
    print_r($row);
}
unset($dbh); unset($stmt);