How to filter unsafe strings in php

How to filter unsafe strings in php: 1. Add "backslash" to special characters through the mysql_real_escape_string function; 2. Add backslash to special characters through the addslashes function; 3. Use htmlentities Functions filter user input data and more.

The operating environment of this article: windows7 system, PHP7.1 version, DELL G3 computer

phpHow to filter unsafe strings? Summary of the use of character security filtering functions in PHP

This article mainly briefly introduces the character security filtering functions in PHP. It is very useful for preventing SQL injection attacks and XSS attacks. It is recommended to everyone here.

In the process of WEB development, we often need to obtain data entered by users from all over the world. However, we "can never trust user-entered data." Therefore, in various web development languages, functions are provided to ensure the security of user input data. In PHP, there are some very useful and convenient functions that can help you prevent problems like SQL injection attacks, XSS attacks, etc.

• mysql_real_escape_string()
  

This function was used to prevent SQL injection attacks in PHP It provides great help. It adds "backslash" to special characters, such as single quotes and double quotes, to ensure that the user's input is safe before using it to query. But you should note that you are using this function while connected to the database.
But now the mysql_real_escape_string() function is basically no longer needed. All new application development should use libraries like PDO to operate the database. In other words, we can use ready-made statements to prevent SQL injection attacks.

• addslashes()
  

This function is very similar to the mysql_real_escape_string() above, The same backslash is added for special characters, but be careful not to use this function when the value of magic_quotes_gpc in the setting file php.ini is "on". When magic_quotes_gpc = on, automatically runs addslashes() on all GET, POST and COOKIE data. Do not use addslashes() on strings that have been escaped by magic_quotes_gpc, as this will result in double escaping. You can check the value of this variable through the get_magic_quotes_gpc() function in PHP.

• 3htmlentities()
  

This function is very useful for filtering user input data. It Characters can be converted into HTML entities. For example, when the user enters the character "<", it will be converted into the HTML entity "<" by this function (you will see "<" when viewing the source code), thus preventing XSS and SQL injection attacks. Unrecognized character sets will be ignored and replaced by ISO-8859-1

• ##htmlspecialchars()
  

This function is very similar to the above. Some characters in HTML have special meanings. If you want to reflect such meanings, they must be converted into HTML entities. This function will return the converted string.

• strip_tags()
  

This function can remove all HTML from the string. JavaScript and PHP tags, of course, you can also ignore filtering some specific tags by setting the second parameter of this function.

• intval()
  

intval is not actually a filtering function; is to convert the variable into an integer type. It is very useful when we need to get an integer parameter. You can use this function to make your PHP code safer, especially when you are parsing integer data such as id and age.

Let’s summarize PHP’s methods for processing special characters in form submissions, which mainly involve the joint use of several functions such as htmlspecialchars/addslashes/stripslashes/strip_tags/mysql_real_escape_string. Let’s communicate with everyone.

1. Several PHP functions related to special character processing

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Function name	Definition	Introduction
htmlspecialchars	will be used with, Convert single and double quotation marks, greater than and less than signs into HTML format	&convert to& "convert to" 'convert to' >convert Into>
htmlentities()	All characters are converted into HTML format	In addition to the above htmlspecialchars characters, it also includes double-byte character display into encoding, etc.
addslashes	Single and double quotes, backslashes and NULL plus backslash escape	The changed characters include single quotation mark ('), double quotation mark ("), backslash backslash (\) and the null character NULL.
stripslashes	Remove backslash characters	Remove backslash characters in the string. If there are two consecutive backslashes, remove one and leave one. If there is only one backslash, just remove it.
quotemeta	Add quotation symbols	Add the backslash "\" symbol in front of characters such as \\ * ? [ ^ ] ( $ ) in the string.
nl2br()	Convert newline characters to
strip_tags	Remove HTML and PHP tags	Remove any HTML tags and PHP tags in the string, including the content between tag blocks. Note that if there are errors in the string HTML and PHP tags, an error will also be returned.
mysql_real_escape_string	Escape special characters in SQL strings	Escape \x00 \n \r Space \ ' " \x1a, which is very effective for multi-byte character processing. mysql_real_escape_string will determine the character set, but mysql_escape_string does not need to be considered.