PHP - setcookie(); not working

Question

I've made a login, that sets a cookie with a value of the imputed email address, so in the global.php file, it stores an array of the users data using:

$email = $_COOKIE["PeopleHub"];
$getuserdata = mysqli_query($con, "SELECT * FROM Earth WHERE email='$email'");
$userdata = mysqli_fetch_array($getuserdata, MYSQLI_ASSOC);

The cookie isn't being set, I know this because I made a test file:

echo $_COOKIE["PeopleHub"];

It just made a blank page.

The login code (where the cookie is set):

<?php 
include "global.php";    
?>
<h2>Login</h2>
<?php 
    echo "We currently have <b>" . $usercount . "</b> members, <b>" . $onlinecount . "</b> of which are online. "; 
?>
<br>
<br>
<?php 
    if(isset($_POST["email"])){ 
        $email = $_POST["email"];
        $password = sha1($_POST["password"]);
        $check = mysqli_query($con, "SELECT * FROM Earth WHERE `email`='$email' AND `password`='$password'");
        $check = mysqli_num_rows($check);
        if($check == 1){
        setcookie("PeopleHub", $email, 0, '/');
        echo "We logged you in!";
        }
        else { 
            echo "We couldn't log you in!";
        }
    }
?>
<form action="<?php echo $_SERVER['REQUEST_URI']; ?>" method="post">
    Email <input name="email" placeholder="Email Address" required="" type="text"><br>
    Password <input name="password" placeholder="Password" required="" type="password"><br>
    <input type="reset" value="Start Over">
    <input type="submit" value="Login">
</form>

Answer 1

You have to set cookies before any headers are sent out.

From the manual:

setcookie() defines a cookie to be sent along with the rest of the HTTP headers. Like other headers, cookies must be sent before any output from your script (this is a protocol restriction). This requires that you place calls to this function prior to any output, including and tags as well as any whitespace.

This means you will need to look into output buffering if you wish to use this code as is.

<?php

ob_start();
echo "Hello\n";

setcookie("cookiename", "cookiedata");

ob_end_flush();

?>

Depending on the contents of global.php, this might work for you. All I did was remove any output before setcookie() is called. If global.php contains any whitespace or HTML output in it this won't work:

<?php 
include "global.php";    

    if(isset($_POST["email"])){ 
        $email = $_POST["email"];
        $password = sha1($_POST["password"]);
        $check = mysqli_query($con, "SELECT * FROM Earth WHERE `email`='$email' AND `password`='$password'");
        $check = mysqli_num_rows($check);
        if($check == 1){
        setcookie("PeopleHub", $email, 0, '/');
        echo "We logged you in!";
        }
        else { 
            echo "We couldn't log you in!";
        }
    }
?>
<h2>Login</h2>
<?php 
    echo "We currently have <b>" . $usercount . "</b> members, <b>" . $onlinecount . "</b> of which are online. "; 
?>
<br>
<br>
<form action="<?php echo $_SERVER['REQUEST_URI']; ?>" method="post">
    Email <input name="email" placeholder="Email Address" required="" type="text"><br>
    Password <input name="password" placeholder="Password" required="" type="password"><br>
    <input type="reset" value="Start Over">
    <input type="submit" value="Login">
</form>