PHP form validation -w3school PHP study notes w3school novice w3school official website w3school tutorial download

Note: Please pay attention to data security when processing forms in PHP
It is very necessary to verify the submitted data before processing the HTML form to prevent hacker intrusions and spam harassment.

The above html form assumes that the following rules apply:
Fields – Validation Rules
Name – required, must contain letters and spaces
Email – required, must contain a valid email address including @ and .
URL (website) – optional, if filled in, it must be a valid URL
Comment – ​​optional, multi-line input field
Gender – required, select one
The html code is as follows:

<code><span>&lt;/<span>head</span>&gt;</span><span>&lt;<span>body</span>&gt;</span><span>&lt;<span>form</span><span>action</span>=<span>'test.php'</span><span>method</span>=<span>'post'</span>&gt;</span>
        姓名:<span>&lt;<span>input</span><span>type</span>=<span>'text'</span><span>name</span>=<span>'name'</span> /&gt;</span><span>&lt;<span>br</span>/&gt;</span>
        电邮:<span>&lt;<span>input</span><span>type</span>=<span>'text'</span><span>name</span>=<span>'email'</span> /&gt;</span><span>&lt;<span>br</span>/&gt;</span>
        网址:<span>&lt;<span>input</span><span>type</span>=<span>'text'</span><span>name</span>=<span>'website'</span> /&gt;</span><span>&lt;<span>br</span>/&gt;</span>
        评论:<span>&lt;<span>textarea</span><span>name</span>=<span>'comment'</span><span>rows</span>=<span>3</span><span>cols</span>=<span>21</span>&gt;</span><span>&lt;/<span>textarea</span>&gt;</span><span>&lt;<span>br</span>/&gt;</span>
        性别:<span>&lt;<span>input</span><span>type</span>=<span>"radio"</span><span>name</span>=<span>'gender'</span><span>value</span>=<span>0</span><span>checked</span>=<span>'checked'</span>/&gt;</span>女性
        <span>&lt;<span>input</span><span>type</span>=<span>"radio"</span><span>name</span>=<span>'gender'</span><span>value</span>=<span>1</span> /&gt;</span>男性<span>&lt;<span>br</span>/&gt;</span><span>&lt;<span>input</span><span>type</span>=<span>'submit'</span><span>value</span>=<span>'提交'</span> /&gt;</span><span>&lt;/<span>form</span>&gt;</span><span>&lt;/<span>body</span>&gt;</span><span>&lt;/<span>html</span>&gt;</span></code>

This form submits data through the post method
Validate form data via PHP:
Generally, when filtering submitted data, the htmlspecialchars() function is used to process the data, which converts html tag characters into html entities. For example, < and > will be replaced by lt; and g t;. This prevents attackers from exploiting the code by injecting HTML or JS code into the form.
After we use the htmlspecailchars() function, the following code

<code><span>&lt;<span>script</span>&gt;</span><span>location.href(<span>'http://www.hacked.com'</span>)</span><span>&lt;/<span>script</span>&gt;</span></code>

will be escaped to:

<code><span>&amp;</span><span>lt</span>;script<span>&amp;</span><span>gt</span>;location<span>.</span>href(<span>'http://www.hacked.com'</span>)<span>&amp;</span><span>lt</span>;/script<span>&amp;</span><span>gt</span>;</code>

. Now the submitted data is safe and it will not cause damage to the page code.
In addition, in addition to filtering data with the htmlspecialchar() function, we also need to do two things:

1. Remove unnecessary characters (such as extra spaces, tabs, newlines, etc.) in user input data, and use PHP more The trim() function
2. removes backslash() from user input data using PHP’s stripslashes() function
   Form data processing example:

<code><span><span>&lt;?php</span><span>$name</span>=<span>$email</span>=<span>$website</span>=<span>$comment</span>=<span>''</span>;
<span>$gender</span>=<span>0</span>;
<span>$name</span>=test_input(<span>$_POST</span>[<span>'name'</span>]);
<span>$email</span>=test_input(<span>$_POST</span>[<span>'email'</span>]);
<span>$website</span>=test_input(<span>$_POST</span>[<span>'website'</span>]);
<span>$comment</span>=test_input(<span>$_POST</span>[<span>'comment'</span>]);

<span><span>function</span><span>test_input</span><span>(<span>$data</span>)</span>{</span><span>$data</span>=trim(<span>$data</span>);<span>//去除$data数据两侧多余的空格</span><span>$data</span>=stripslashes(<span>$data</span>);<span>//去除$data中的反斜杠</span><span>$data</span>=htmlspecialchars(<span>$data</span>);<span>//将html标签转以为html实体</span><span>return</span><span>$data</span>;
}


<span>?&gt;</span></span></code>

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