http://ayende.comAyende @ RahienCopyright (C) Ayende Rahien 2004 - 2021 (c) 202660"0x" is a hex specifier with ancestry back into the deep mists of "C" history. It's related to "0" for base 8: 27 == 033 == 0x1B I'm not sure where it came from, but Delphi's Object Pascal language used $ to prefix int constants. Also, the W3C uses "#" in the CSS specification. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment12http://ayende.com/4489/what-the-hell-hex-number-parsing#comment12Fri, 07 May 2010 23:58:51 GMTI guess the "0x" is a text-editor "atrefact"? In reality, the hex number is 9F, not 0x9F. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment11http://ayende.com/4489/what-the-hell-hex-number-parsing#comment11Fri, 07 May 2010 16:52:30 GMTThe .NET 4 page for the three-argument Int64.Parse method includes this additional tidbit following the Non-composite NumberStyles values table: "If the NumberStyles.AllowHexSpecifier flag is used, s must be a hexadecimal value." Source: [msdn.microsoft.com/.../8b520kdx%28v=VS.100%29.aspx](http://msdn.microsoft.com/en-us/library/8b520kdx%28v=VS.100%29.aspx)http://ayende.com/4489/what-the-hell-hex-number-parsing#comment10http://ayende.com/4489/what-the-hell-hex-number-parsing#comment10Fri, 07 May 2010 01:26:12 GMTYou do not need both, NumberStyles.AllowHexSpecifier and NumberStyles.HexNumber, values. NumberStyles.HexNumber equals to AllowLeadingWhite | AllowTrailingWhite | AllowHexSpecifier. And I agree with everyone about the bad naming of the hex specifier. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment9http://ayende.com/4489/what-the-hell-hex-number-parsing#comment9Fri, 07 May 2010 00:58:33 GMTAyende, As i remember: it isn't AllowHexSpecieir that makes the 0x prefix fail, i have never found a way to have long.Parse accept the prefix so i have used: Convert.ToInt64("0x9f", 16); Which is the same i asume you ended up with. But i agree with you, the naming of AllowHexSpecifier is REALLY confusing. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment8http://ayende.com/4489/what-the-hell-hex-number-parsing#comment8Fri, 07 May 2010 00:43:10 GMTI think AllowHexSpecifier is horribly named. But the documentation is quite clear: The s parameter contains a number of the form: [ws][sign]digits[ws] Or, if style includes AllowHexSpecifier: [ws]hexdigits[ws] ... hexdigits A sequence of hexadecimal digits from 0 through f, or 0 through F. AllowHexSpecifier tells Parse to treat the number as hexadecimal. HexNumber does the same, but also allows Whitespace before/after. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment7http://ayende.com/4489/what-the-hell-hex-number-parsing#comment7Fri, 07 May 2010 00:35:38 GMTAre you reading these docs? [msdn.microsoft.com/.../...obalization.numberstyles](http://msdn.microsoft.com/en-us/library/system.globalization.numberstyles)(VS.80).aspx Although its contra-intuitive (wouldn't be the first time) it says: "AllowHexSpecifier - Indicates that the numeric string represents a hexadecimal value. Valid hexadecimal values include the numeric digits 0-9 and the hexadecimal digits A-F and a-f. Hexadecimal values can be left-padded with zeros. Strings parsed using this style are not permitted to be prefixed with "0x". " Normally in these situations I support the right behaviour by wrapping it in a 'int FromHex(this string)' extension method and move on until a better solution crosses my path. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment6http://ayende.com/4489/what-the-hell-hex-number-parsing#comment6Fri, 07 May 2010 00:34:57 GMTUncle Festis & Demis, I don't _want_ to drop that. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment5http://ayende.com/4489/what-the-hell-hex-number-parsing#comment5Fri, 07 May 2010 00:23:02 GMT Jakob, Thanks, I missed the not. But What is up with _Allow_HexSpecifier, the only hex specifier that _I_ know of is 0x And removing that from the bit pattern doesn't help: NumberStyles.HexNumber & ~NumberStyles.AllowHexSpecifier http://ayende.com/4489/what-the-hell-hex-number-parsing#comment4http://ayende.com/4489/what-the-hell-hex-number-parsing#comment4Fri, 07 May 2010 00:22:39 GMTOren, dropping the '0x' prefix should work, e.g: long.Parse("9f", NumberStyles.HexNumber) http://ayende.com/4489/what-the-hell-hex-number-parsing#comment3http://ayende.com/4489/what-the-hell-hex-number-parsing#comment3Fri, 07 May 2010 00:11:23 GMTFrom the documentation of NumberStyle.AllowHexSpecifier 'Strings parsed using this style are not permitted to be prefixed with "0x".' btw. NumberStyles.HexNumber includes AllowHexSpecifier already. http://ayende.com/4489/what-the-hell-hex-number-parsing#comment2http://ayende.com/4489/what-the-hell-hex-number-parsing#comment2Fri, 07 May 2010 00:11:11 GMTIt no likey the "0x" at the beginning? http://ayende.com/4489/what-the-hell-hex-number-parsing#comment1http://ayende.com/4489/what-the-hell-hex-number-parsing#comment1Fri, 07 May 2010 00:10:55 GMT