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Re: Der Fickfinger im Betreff
- To: firstname.lastname@example.org
- Subject: Re: Der Fickfinger im Betreff
- From: email@example.com (Lutz Donnerhacke)
- Date: 21 Jul 1998 12:46:56 GMT
- Comment: This message comes from the debate mailing list.
- Newsgroups: iks.lists.fitug
- Organization: IKS GmbH Jena
- References: <firstname.lastname@example.org>
- Sender: email@example.com
* Wau Holland wrote:
>Umgekehrt brachte Lutz Schicht 8 auf, mit den Worten von
>Holger Reif: das, was der Anwender wirklich will.
Dazu muß man historisch korrekt bemerken, daß es sich hier um einen
einfachen Obi-Wan Error handelt.
obi-wan error /oh'bee-won er'*r/ /n./
[RPI, from off-by-one' and the Obi-Wan Kenobi character in "Star Wars"]
A loop of some sort in which the index is off by 1. Common when the
index should have started from 0 but instead started from 1. A kind of
off-by-one error. See also zeroth.
off-by-one error /n./
Exceedingly common error induced in many ways, such as by starting at 0
when you should have started at 1 or vice-versa, or by writing < N
instead of <= N or vice-versa. Also applied to giving something to the
person next to the one who should have gotten it. Often confounded with
fencepost error, which is properly a particular subtype of it.
zeroth /zee'rohth/ /adj./
First. Among software designers, comes from C's and LISP's 0-based
indexing of arrays. Hardware people also tend to start counting at 0
instead of 1; this is natural since, e.g., the 256 states of 8 bits
correspond to the binary numbers 0, 1, ..., 255 and the digital devices
known as counters' count in this way.
Hackers and computer scientists often like to call the first chapter of
a publication chapter 0', especially if it is of an introductory nature
(one of the classic instances was in the First Edition of K&R). In
recent years this trait has also been observed among many pure
mathematicians (who have an independent tradition of numbering from 0).
Zero-based numbering tends to reduce fencepost errors, though it cannot
eliminate them entirely.
fencepost error /n./
1. A problem with the discrete equivalent of a boundary condition, often
exhibited in programs by iterative loops. From the following problem:
"If you build a fence 100 feet long with posts 10 feet apart, how
many posts do you need?" (Either 9 or 11 is a better answer than the
obvious 10.) For example, suppose you have a long list or array of
items, and want to process items m through n; how many items are
there? The obvious answer is n - m, but that is off by one; the right
answer is n - m + 1. A program that used the obvious' formula would
have a fencepost error in it. See also zeroth and off-by-one error,
and note that not all off-by-one errors are fencepost errors. The
game of Musical Chairs involves a catastrophic off-by-one error where
N people try to sit in N - 1 chairs, but it's not a fencepost error.
Fencepost errors come from counting things rather than the spaces
between them, or vice versa, or by neglecting to consider whether one
should count one or both ends of a row.
2. [rare] An error induced by unexpected regularities in input values,
which can (for instance) completely thwart a theoretically efficient
binary tree or hash table implementation. (The error here involves
the difference between expected and worst case behaviors of an
PS: Zur Versöhnung: