header函数没有重定向到home.php，为什么？

Here i am using header function to redirect to home.php after login, but header function is not redirecting to that page. Even when i run same code on my local computer it works fine.

<?php
ob_start();
session_start();
require_once 'phpconnection.php';
// it will never let you open index(login) page if session is set
if ( isset($_SESSION['user'])!="" ) {
 header("Location:home.php");
 exit;
}
$error = false;
 if( isset($_POST['btn-logIn']) ) { 
// prevent sql injections/ clear user invalid inputs
 $email = trim($_POST['email']);
$email = strip_tags($email);
$email = htmlspecialchars($email);

$pass = trim($_POST['password']);
$pass = strip_tags($pass);
$pass = htmlspecialchars($pass);
// prevent sql injections / clear user invalid inputs
 if ( !filter_var($email,FILTER_VALIDATE_EMAIL) ) {
 $error = true;
 $errMsg = "Please enter valid email address.";
}
// if there's no error, continue to login
if (!$error) {
 $res=mysql_query("SELECT userId, userfName, userlName,userPassword FROM       userdata WHERE userEmail='$email'");
 $row=mysql_fetch_array($res);
 $count = mysql_num_rows($res); // if uname/pass correct it returns must be 1 row
 if( $count == 1 && $row['userPassword']==$pass  ) {
  $_SESSION['user'] = $row['userId'];
   header("Location:home.php");
 } else {
  $errMsg = "Try again...";
 }
}
}
 ?>

Try your code with this code,

<?php
ob_start();
session_start();

if ( isset($_SESSION['user'])!="" ) {
 header("Location:home.php");
 exit;
}

require_once 'phpconnection.php';
// it will never let you open index(login) page if session is set

?>

You do not need the !="" on line 5 because isset() already checks for existence. Either its there or its not.

if (isset($_SESSION['user'])){
    header("Location: home.php");
    exit;
} else {
    echo "something here";
}

You can use !isset() to get the opposite result as well.