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Unit 5: Strings

Attributes in preserved tags are not changed by strip_tags( ). Because attributes such as style Notes
and onmouseover can affect the look and behaviour of web pages, preserving some tags with
strip_tags() would not necessarily remove the potential for abuse.

Extracting Meta Tags
If you have the HTML for a web page in a string, the get_meta_tags( ) function returns an array of
the meta tags in that page. The name of the meta tag (keywords,author, description, etc.) becomes
the key in the array, and the content of the meta tag becomes the corresponding value:
$meta_tags = get_meta_tags(‘http://www.example.com/’); echo “Web page made by {$meta_
tags[author]}”; Web page made by Pradip

The general form of the function is:
$array = get_meta_tags(filename [, use_include_path]);
Pass a true value for use_include_path to let PHP attempt to open the file using the standard
include path.

5.5.2 URLs
PHP provides functions to convert to and from URL encoding, which allows you to build and
decode URLs. There are actually two types of URL encoding, which differ in how they treat
spaces. The first (specified by RFC 1738) treats a space as just another illegal character in a URL
and encodes it as %20. The second (implementing the application/x-www-form-urlencoded
system) encodes a space as a + and is used in building query strings.
RFC 1738 Encoding and Decoding

To encode a string according to the URL conventions, use rawurlencode( ):
$output = rawurlencode(input);
This function takes a string and returns a copy with illegal URL characters encoded in the %dd
convention.
If you are dynamically generating hypertext references for links in a page, you need to convert
them with rawurlencode( ):

$name = “Programming PHP”; $output = rawurlencode($name); echo “http://
localhost/$output”;http://localhost/Programming%20PHP
The rawurldecode( ) function decodes URL-encoded strings:

$encoded = ‘Programming%20PHP’; echo rawurldecode($encoded); Programming PHP
Query-string Encoding
The urlencode( ) and urldecode( ) functions differ from their raw counterparts only in that they
encode spaces as plus signs (+) instead of as the sequence %20. This is the format for building
query strings and cookie values, but because these values are automatically decoded when they
are passed through a form or cookie, you do not need to use these functions to process the current
page’s query string or cookies. The functions are useful for generating query strings:
$base_url = ‘http://www.google.com/q=’; $query = ‘PHP sessions -cookies’; $url = $base_url .
urlencode($query); echo $url;http://www.google.com/q=PHP+sessions+-cookies
5.5.3 SQL

Most database systems require that string literals in your SQL queries be escaped. SQL’s encoding
scheme is pretty simple—single quotes, double quotes, NUL-bytes, and backslashes need to be
preceded by a backslash. The addslashes( ) function adds these slashes, and the stripslashes( )
function removes them:

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