PHP development skills: How to implement form validation function

PHP Development Tips: How to Implement Form Validation Function

Introduction:
In web development, form validation is a very important part. It can ensure that the data submitted by users meets expectations and effectively prevent malicious attacks and problems caused by incorrect data. This article will introduce how to use PHP to implement form validation functions and provide specific code examples.

1. Front-end form verification:
Before performing form verification on the server side, we usually perform front-end form verification first. Front-end form validation can provide timely feedback and reduce the load on the server. The following are some commonly used front-end form validation methods:

1. Required field validation:

   <input type="text" name="username" required>

   By setting the required attribute, you can ensure that the user must fill in the field.

2. Input format validation:
   Use the input types provided by HTML5 to limit the format of user input. For example:

   <input type="email" name="email">

   The above code will ensure that the content entered by the user conforms to the format of the email.

3. Custom rule validation:
   Use JavaScript to write custom validation rules. For example:

   <input type="text" name="age" onblur="validateAge(this.value)">
   <script>
   function validateAge(value) {
     if (value < 18) {
    alert("未满18岁，不可注册！");
     }
   }
   </script>

   The above code calls the validateAge function through the onblur event for age verification.

2. Server-side form verification:
Front-end form verification is only a basic verification method. In order to ensure the accuracy and security of data, we also need to perform it on the server side. form validation.

The following are some commonly used server-side form verification methods:

1. Judging whether to submit:
   First, we need to determine whether the form has been submitted. The following code example demonstrates a basic commit decision.

   if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // 表单已提交
    // 进行表单验证逻辑
   } else {
    // 表单未提交
    // 显示表单页面
   }

2. Required field validation:
   Validate by checking whether the required fields in the form are empty. The following code example demonstrates how to verify that the username and password are empty.

   if (empty($_POST["username"]) || empty($_POST["password"])) {
    echo "用户名和密码不能为空！";
   }

3. Data format verification:
   Use regular expressions or built-in functions to verify whether the data format entered by the user is correct according to the type and length limit of the field. The following code example demonstrates how to verify that the mailbox format is correct.

   if (!filter_var($_POST["email"], FILTER_VALIDATE_EMAIL)) {
    echo "邮箱格式不正确！";
   }

4. Data security verification:
   In order to ensure the security of data, data filtering and escaping are required. The following code example demonstrates how to prevent SQL injection attacks.

   $name = $_POST["name"];
   $name = mysqli_real_escape_string($conn, $name);
   $query = "SELECT * FROM users WHERE name='$name'";

5. Error message display:
   Finally, during the verification process, if an error is found, the error message needs to be displayed to the user. The following code example demonstrates how to display an error message.

   $errors = array();
   
   if (empty($_POST["username"])) {
    $errors[] = "用户名不能为空！";
   }
   
   if (empty($_POST["password"])) {
    $errors[] = "密码不能为空！";
   }
   
   if (!empty($errors)) {
    foreach ($errors as $error) {
        echo $error . "<br>";
    }
   }

Conclusion:
Through the combination of front-end form validation and server-side form validation, we can effectively implement the form validation function. This not only improves the user experience but also protects the server from attacks. I hope the content of this article can be helpful to you, thank you for reading!

The above is the detailed content of PHP development skills: How to implement form validation function. For more information, please follow other related articles on the PHP Chinese website!