Difference between Url Encode and HTML encode

What’s the difference between an URL Encode and a HTML Encode?

HTML Encoding escapes special characters in strings used in HTML documents to prevent confusion with HTML elements like changing

"<hello>world</hello>" 

to

"<hello>world</hello>"

URL Encoding does a similar thing for string values in a URL like changing

"hello+world = hello world"

to

"hello%2Bworld+%3D+hello+world"

urlEncode replaces special characters with characters that can be understood by web browsers/web servers for the purpose of addressing... hence URL. For instance, spaces are replaced with %20, ' = %27 etc...

See these references:

• http://www.blooberry.com/indexdot/html/topics/urlencoding.htm
• http://www.degraeve.com/reference/urlencoding.php

HtmlEncode replaces special characters with character strings that are recognised by the HTML engine itself to render the content of the page - things like & become & or < = <, > = > this prevents the HTML engine from interpreting these characters as parts of the HTML markup and therefore render them as if they were strings.

See this reference:

• http://msdn.microsoft.com/en-us/library/ms525347.aspx

Both HTML and URL's are essentially very constrained languages. As a language they add meaning to specific keywords or operators. For both of these languages though, keywords are almost always single characters. For example

• HTML: > and <
• URL: / and :

In the use of each language though it is possible to use these constructs in a manner that does not ensure the meaning of the language. For instance this post contains a > character. I do not want it to be interpreted as HTML, just text.

This is where Encode and Decode methods come into play. These methods will respectively take a string and convert any of the characters that would otherwise be treated as keywords into an escaped form which will not be interpreted as part of the language.

For instance: Passing > into HtmlEncode will return &gt;

HTMLEncode and URLEncode deal with invalid characters in HTML and URLs, or more accurately, characters that need to be specially written to be interpreted correctly. For example, in HTML the < and > characters are used to indicate tags. Thus, if you wanted to write a math formula, something like 1+1 < 2+2, the '<' would normally be interpreted as the beginning of a tag. HTMLEncoding turns this character into "&lt;" which is the encoded representation of the less-than sign. URLEncoding does the same, but for URLs, for which the special characters are different, although there is some overlap.

I don't know what language you are working in, but the PHP manual for example provides good explanations.

> URLEncode > > Returns a string in which all > non-alphanumeric characters except -_. > have been replaced with a percent (%) > sign followed by two hex digits and > spaces encoded as plus (+) signs. It > is encoded the same way that the > posted data from a WWW form is > encoded, that is the same way as in > application/x-www-form-urlencoded > media type. This differs from the » > RFC 1738 encoding (see rawurlencode()) > in that for historical reasons, spaces > are encoded as plus (+) signs.

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