Why are Hexadecimal Prefixed as 0x and not anything else? I understand the usage of prefix but I dont understand the significance of 0x.
+2
A:
It appears to have stemmed from a C convention: http://en.wikipedia.org/wiki/Hexadecimal#Representing_hexadecimal .
wsh
2010-04-19 20:34:55
-1. The article merely states that C uses `0x`. But we already knew that. The question is *why*. Wikipedia gives no reason, and it says nothing about it being a convention.
Rob Kennedy
2010-04-19 23:10:30
Examine the tags of the question itself; presumably the generalized reference has to do with the predominance of Unix and C. Furthermore, it seems that before C this was not a way to refer to hex numbers.
wsh
2010-04-20 01:01:12
Right. The tags (added by Roygbiv, not Kunjaan) tell us the question is about C and other languages. In other words, the question asks, "Why are hexadecimals prefixed with `0x` in C, C++, and C#?" And your answer is to say that C uses `0x`? You're adding no new information; you're just begging the question. And if `0x` wasn't used prior to C, then that's all the more reason to wonder why it was done that way in C.
Rob Kennedy
2010-04-20 01:19:51
Okay, fair enough.
wsh
2010-04-20 04:17:39
@Rob: actually, the question is "what does `0x` mean"; it's simply a prefix indicating that what follows is an integer constant in hex format. As to *why* `0x` over some other prefix, I suspect it was a totally arbitrary decision; there's certainly nothing in the standard or in any of my other references as to why that sequence was used as opposed to something else.
John Bode
2010-04-20 13:45:57
+13
A:
Note: I don't know the correct answer, but the below is just my personal speculation!
As has been mentioned a 0 before a number means it's octal:
04524 // octal, leading 0
Imagine needing to come up with a system to denote hexadecimal numbers, and note we're working in a C style environment. How about ending with h like assembly? Unfortunately you can't - it would allow you to make tokens which are valid identifiers (eg. you could name a variable the same thing) which would make for some nasty ambiguities.
8000h // hex
FF00h // oops - valid identifier! Hex or a variable or type named FF00h?
You can't lead with a character for the same reason:
xFF00 // also valid identifier
Using a hash was probably thrown out because it conflicts with the preprocessor:
#define ...
#FF00 // invalid preprocessor token?
In the end, for whatever reason, they decided to put an x after a leading 0 to denote hexadecimal. It is unambiguous since it still starts with a number character so can't be a valid identifier, and is probably based off the octal convention of a leading 0.
0xFF00 // definitely not an identifier!
AshleysBrain
2010-04-19 21:20:18
Interesting. I imagine they could have used a leading 0 AND trailing h to denote hex. The trailing h probably would have been confused with the type specifier suffix, e.g. 0xFF00l vs 0FF00hl
zdan
2010-04-20 00:24:03
This argument implies that the use of a leading zero to denote octal numbers predates the use of the hexadecimal "0x" prefix. Is this true?
Andreas Rejbrand
2010-04-22 13:09:10
Wouldn't they have both been invented at the same time? Why would there ever be one but not the other?
AshleysBrain
2010-04-22 13:28:00
A:
0x simply indicates that the following digits represent an integer value in hex notation (base 16). The grammar is
hexadecimal-constant:
0x hex-digit
0X hex-digit
hexadecimal-constant hex-digit
where
hex-digit: one of
0 1 2 3 4 5 6 7 8 9
A B C D E F a b c d e f
Thus, 0x10 means "interpret the integer constant 10 in base 16, not base 10".
As to why C uses 0x as opposed to some other indicator, I suspect that was an entirely arbitrary decision by the language designers. It's consistent with using a leading 0 to indicate an octal constant. I haven't found a rationale for it in any of my references or the language standard (although I haven't looked all that hard).
John Bode
2010-04-20 13:57:34