PHP determines whether the user has logged in. If logged in, the home page will be displayed. If not, enter the login page or registration page

login.php

I use it here session Instead of cookie, Think the same ,session The code is simpler to operate , Easier to demonstrate .

<?php
    $user = ... ...; // Here is the data about users queried by the database 
    if ($user != null || $user != "") {
        // Here are the settings cookie, It needs to be opened before use cookie, I used it here session, Think the same ,session concise , Easy to demonstrate .
        //setcookie("user", $user['user_id'], time() + 1 * 24 * 3600);

        // Turn on session
        session_start();
        // In the data 
        $_SESSION['user'] = $user['user_id'];
        // After saving, jump to the home page 
        echo "<script>window.location.href='index.php'</script>";
    } else {
        echo "<script>alert(' Wrong account or password ！')</script>";
    }
?>

index.php

This is the home page , Judgment is needed , If you pass session User information is found , Then the corresponding content is displayed .

?php
    // Injected into database operations PHP file （ It is easier to operate the database ）, I have previously posted a blog about database static tools ,
    // Blog links ：https://blog.csdn.net/qfxl0724/article/details/125847351
    include_once "DBHelper.php";
    // Use session To determine whether the user is logged in 
    session_start();
    // Use variables to receive session Information of users in 
    $user = $_SESSION['user'];
    if ($user == null || $user == '') {
        echo "<a class='login' href='login.php'> Sign in </a>";
        echo "<a class='enroll' href='enroll.php'> register </a>";
    } else {
        echo "<a class='myspace' href='user/index.php'> My home page </a>";
    }
?>