How do you UrlEncode without using System.Web?

The answers here are very good, but still insufficient for me.

I wrote a small loop that compares Uri.EscapeUriString with Uri.EscapeDataString for all characters from 0 to 255.

NOTE: Both functions have the built-in intelligence that characters above 0x80 are first UTF-8 encoded and then percent encoded.

Here is the result:

******* Different *******

'#' -> Uri "#" Data "%23"
'$' -> Uri "$" Data "%24"
'&' -> Uri "&" Data "%26"
'+' -> Uri "+" Data "%2B"
',' -> Uri "," Data "%2C"
'/' -> Uri "/" Data "%2F"
':' -> Uri ":" Data "%3A"
';' -> Uri ";" Data "%3B"
'=' -> Uri "=" Data "%3D"
'?' -> Uri "?" Data "%3F"
'@' -> Uri "@" Data "%40"


******* Not escaped *******

'!' -> Uri "!" Data "!"
''' -> Uri "'" Data "'"
'(' -> Uri "(" Data "("
')' -> Uri ")" Data ")"
'*' -> Uri "*" Data "*"
'-' -> Uri "-" Data "-"
'.' -> Uri "." Data "."
'_' -> Uri "_" Data "_"
'~' -> Uri "~" Data "~"

'0' -> Uri "0" Data "0"
.....
'9' -> Uri "9" Data "9"

'A' -> Uri "A" Data "A"
......
'Z' -> Uri "Z" Data "Z"

'a' -> Uri "a" Data "a"
.....
'z' -> Uri "z" Data "z"

******* UTF 8 *******

.....
'Ò' -> Uri "%C3%92" Data "%C3%92"
'Ó' -> Uri "%C3%93" Data "%C3%93"
'Ô' -> Uri "%C3%94" Data "%C3%94"
'Õ' -> Uri "%C3%95" Data "%C3%95"
'Ö' -> Uri "%C3%96" Data "%C3%96"
.....

EscapeUriString is to be used to encode URLs, while EscapeDataString is to be used to encode for example the content of a Cookie, because Cookie data must not contain the reserved characters '=' and ';'.

System.Uri.EscapeUriString() can be problematic with certain characters, for me it was a number / pound '#' sign in the string.

If that is an issue for you, try:

System.Uri.EscapeDataString() //Works excellent with individual values

Here is a SO question answer that explains the difference:

What's the difference between EscapeUriString and EscapeDataString?

and recommends to use Uri.EscapeDataString() in any aspect.

You can use

Uri.EscapeUriString (see http://msdn.microsoft.com/en-us/library/system.uri.escapeuristring.aspx)

In .Net 4.5+ use WebUtility

Just for formatting I'm submitting this as an answer.

Couldn't find any good examples comparing them so:

string testString = "http://test# space 123/text?var=val&another=two";
Console.WriteLine("UrlEncode:         " + System.Web.HttpUtility.UrlEncode(testString));
Console.WriteLine("EscapeUriString:   " + Uri.EscapeUriString(testString));
Console.WriteLine("EscapeDataString:  " + Uri.EscapeDataString(testString));
Console.WriteLine("EscapeDataReplace: " + Uri.EscapeDataString(testString).Replace("%20", "+"));

Console.WriteLine("HtmlEncode:        " + System.Web.HttpUtility.HtmlEncode(testString));
Console.WriteLine("UrlPathEncode:     " + System.Web.HttpUtility.UrlPathEncode(testString));

//.Net 4.0+
Console.WriteLine("WebUtility.HtmlEncode: " + WebUtility.HtmlEncode(testString));
//.Net 4.5+
Console.WriteLine("WebUtility.UrlEncode:  " + WebUtility.UrlEncode(testString));

Outputs:

UrlEncode:             http%3a%2f%2ftest%23+space+123%2ftext%3fvar%3dval%26another%3dtwo
EscapeUriString:       http://test#%20space%20123/text?var=val&another=two
EscapeDataString:      http%3A%2F%2Ftest%23%20space%20123%2Ftext%3Fvar%3Dval%26another%3Dtwo
EscapeDataReplace:     http%3A%2F%2Ftest%23+space+123%2Ftext%3Fvar%3Dval%26another%3Dtwo

HtmlEncode:            http://test# space 123/text?var=val&another=two
UrlPathEncode:         http://test#%20space%20123/text?var=val&another=two

//.Net 4.0+
WebUtility.HtmlEncode: http://test# space 123/text?var=val&another=two
//.Net 4.5+
WebUtility.UrlEncode:  http%3A%2F%2Ftest%23+space+123%2Ftext%3Fvar%3Dval%26another%3Dtwo

In .Net 4.5+ use WebUtility.UrlEncode

This appears to replicate HttpUtility.UrlEncode (pre-v4.0) for the more common characters:
Uri.EscapeDataString(testString).Replace("%20", "+").Replace("'", "%27").Replace("~", "%7E")
Note: EscapeUriString will keep a valid uri string, which causes it to use as many plaintext characters as possible.

See this answer for a Table Comparing the various Encodings:
https://stackoverflow.com/a/11236038/555798

Line Breaks All of them listed here (other than HttpUtility.HtmlEncode) will convert "\n\r" into %0a%0d or %0A%0D

Please feel free to edit this and add new characters to my test string, or leave them in the comments and I'll edit it.