How to use forms in php?

With the development of Internet technology, forms have become an indispensable part of website development. In PHP programming, forms are also commonly used tools. Forms can collect and submit user-entered data, allowing interaction between the website and the user. In this article, we will discuss about PHP forms.

1. The basic concept of a form

A form is composed of HTML code, which can be used to submit data entered by the user. It contains a variety of different HTML tags, such as forms and input boxes. , drop-down menu, etc.

A basic HTML form looks like this:

<form action="form_processing.php" method="post">
  <label for="name">Name:</label>
  <input type="text" name="name" id="name">
  <input type="submit" value="Submit">
</form>

Among them, <form> is the start tag of the form, and its action attribute specifies A script for back-end processing of form data. The method attribute specifies the method used to submit the form, which can be POST or GET.

Each input element in the form needs to specify the name attribute so that the back-end program can obtain the data entered by the user. In the above example, <input> is an input element, the type is text, name is name, it will receive Entered username. <label>The label is used to specify the label of the input box.

2.PHP form processing

Through HTML forms, user input data can already be collected, but these data are not actually processed. In PHP, a backend program is required to process the form and store the data in the database.

First of all, to establish a connection between the front end and the back end, the processing logic for form submission needs to be defined in a PHP file. This script file can be specified in the action attribute of the form, for example:

<form action="form_processing.php" method="post">
  <!-- 表单元素 -->
</form>

In this PHP file, you can use the $_POST super global array to get the submitted Form data. For example, in the above example, we can use the following PHP code to get the name entered by the user:

$name = $_POST['name'];

As you can see, the 'name'## of the $_POST array The # key corresponds to the name attribute previously set in HTML. If you need to get multiple form elements, you can use a similar method to get the values ​​of other elements. Note that the $_POST array can only be used when the submission method is POST.

3. Form data verification

The basic form processing process needs to verify the data entered by the user to ensure that the entered data meets expectations and that no invalid, malicious or dangerous content is entered. In PHP, you can use regular expressions and built-in functions to validate form data.

For example, if you want to check whether the entered email meets the criteria, you can use the

filter_var() function in PHP:

$email = $_POST['email'];
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
  // 邮件地址格式正确
} else {
  // 邮件地址格式不正确
}

You can also use

preg_match( ) function to use regular expressions to validate form data:

if (preg_match('/^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$/', $_POST['email'])) {
  // 邮件地址格式正确
} else {
  // 邮件地址格式不正确
}

4. Form security

Security issues need to be considered when using forms to prevent users from entering arbitrary data and cross-site requests Forgery (CSRF) attacks and other issues. Here are a few suggestions:

Validate all form inputs to ensure the data entered is as expected;
• Use PHP built-in functions, filters, and regular expressions to validate data;
• Never trust user-entered data, including HTML, JavaScript and CSS code, etc.;
• Use an SSL certificate to encrypt form submissions to prevent data from being maliciously hijacked;
• In the form Add hidden domains to prevent CSRF attacks.

Summary

This article introduces how to process forms in PHP, including establishing HTML forms, processing form data through back-end scripts, verifying form data, and how to ensure the security of the form. . Use forms to collect data entered by users and help the website interact better with users. While form processing and validation can be cumbersome, they are an important means of ensuring the security of your site and ensuring that you are getting the correct data.

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