How to use PHP functions to implement user login and logout functions?

M66 2025-06-05

Overview of PHP's user login and logout functions

In web development, user login and logout are one of the most basic and important functions. This article will use a simple example to explain in detail how to use PHP functions to implement a complete user login and logout process.

Step 1: Create a user information database

First, a database needs to be created to save the user's username and password. Here is an example SQL code for creating databases and data tables:

CREATE DATABASE user_info;
USE user_info;
CREATE TABLE users (
  id INT AUTO_INCREMENT PRIMARY KEY,
  username VARCHAR(255) NOT NULL,
  password VARCHAR(255) NOT NULL
);

Step 2: Write a user login page

Next, a login form page is needed to collect the account number and password entered by the user.

<!DOCTYPE html>
<html>
<head>
  <title>Login</title>
</head>
<body>
  <h1>Login</h1>
  <form action="login.php" method="POST">
    <label for="username">Username:</label>
    <input type="text" name="username" id="username" required><br>
    <label for="password">Password:</label>
    <input type="password" name="password" id="password" required><br>
    <input type="submit" value="Login">
  </form>
</body>
</html>

Step 3: Process the login request

After the user submits the form, it will jump to the login processing page. This page will verify the account password and enable Session.

<?php
session_start();

// Get form data
$username = $_POST['username'];
$password = $_POST['password'];

// Connect to the database
$mysqli = new mysqli('localhost', 'username', 'password', 'user_info');

// Query user information
$query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = $mysqli-> query($query);

//Judge login status if ($result->num_rows == 1) {
  $_SESSION[&#39;username&#39;] = $username;
  header(&#39;Location: welcome.php&#39;);
} else {
  echo &#39;Invalid username or password.&#39;;
}
?>

Step 4: Create a welcome page

After logging in successfully, jump to the welcome page. If you are not logged in, you will automatically redirect back to the login page.

<?php
session_start();

if (isset($_SESSION['username'])) {
  $username = $_SESSION['username'];
  echo "Welcome, $username! ";
  echo '<a href="logout.php"> Logout &#39;;
} else {
  header(&#39;Location: login.php&#39;);
}
?>

Step 5: Create a logout function

After the user clicks to log out, the Session should be cleared and redirected back to the login page.

<?php
session_start();
session_unset();
session_destroy();

header('Location: login.php');
?>

Summarize

Through PHP combined with MySQL database, a simple user login and logout function can be quickly implemented. It is recommended to encrypt and store passwords in actual projects (such as using password_hash() ), add verification code functions, and use prepared statements to prevent SQL injection to enhance system security.

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