htmlentities & htmlspecialchars in php

htmlentities 

Convert all applicable characters to HTML entities

$str = "A 'quote' is <b>bold</b>";

Example
echo htmlentities($str);
// Outputs: A 'quote' is &lt;b&gt;bold&lt;/b&gt;



htmlspecialchars 

Convert special characters to HTML entities

'&' (ampersand) becomes '&amp;' 
'<' (less than) becomes '&lt;' 

Example
$new = htmlspecialchars("<a href='test'>Test</a>", ENT_QUOTES);
echo $new; //Outputs:  &lt;a href=&#039;test&#039;&gt;Test&lt;/a&gt;

(Uniform Resource Locator ) urlencode & urldecode in php

urlencode & urldecode in php

urlencode  — This function returns the string output

URL is converted into a valid ASCII format.
URL Encoding space is replaced by %20

Example
urlencode('Hello milind') return output ==>> Hello%20milind 

another example
urlencode('http://www.mywebsite.com/index.php?name=milind chaudhari&id=25');

Output is http://www.mywebsite.com/index.php?name=milind%20chaudhari&id=25

urldecode  — This function returns the string output
Decodes URL-encoded string

Returns the decoded string.

Example
urldecode('http://www.mywebsite.com/index.php?name=milind%20chaudhari&id=25');

Output
http://www.mywebsite.com/index.php?name=milind chaudhari&id=25