PHP filters and processes special characters in Form submission

PHP summarizes the handling methods for special characters in Form submission, mainly involving htmlspecialchars, addslashes, stripslashes, strip_tags, mysql_real_escape_string, and other functions for joint use.

I. Several PHP functions related to special character processing

Function Name	Meaning	Introduction
Htmlspecialchars	Convert the Ampersand, single double quotation marks, greater than or less than sign into HTML Format	& Convert & "Convert" 'Convert' <Converted to < > Convert to>
Htmlentities ()	Convert all characters to HTML Format	In addition to the above htmlspecialchars characters, the two-byte characters are also displayed as encoding.
Addslashes	Double quotation marks, backslash, and NULL plus backslash escape	The modified characters include single quotation marks ('), double quotation marks ("), backslash (\), and NULL.
Stripslashes	Remove backslash characters	Removes the backslash from the string. If there are two backslash lines in a row, remove one and leave one. If there is only one backslash, remove it directly.
Quotemeta	Add a reference symbol	Include. \ + * in the string *? [^] ($) And other characters are preceded by the Backslash "\" symbol.
Nl2br ()	Convert line breaks
Strip_tags	Remove HTML and PHP tags	Remove any HTML and PHP tags in the string, including the contents between Mark blocking. Note: If the HTML and PHP tags of the string are incorrect, an error is returned.
Mysql_real_escape_string	Escape special characters in SQL strings	Escape \ x00 \ n \ r space \ '"\ x1a, which is very effective for processing multi-byte characters. Mysql_real_escape_string determines the character set, and mysql_escape_string does not need to be considered.