|
An elephant in Cairo is a term used in computer programming to describe a piece of data inserted at the end of a search space, which matches the search criteria, in order to make sure the search algorithm terminates; it is a humorous example of a sentinel value. The term derives from a humorous essay circulated on the Internet and published in ''Byte'' magazine in September 1989 that described how various professions would go about hunting elephants. ==Algorithm== When hunting elephants, the article describes programmers as following this algorithm: :# Go to Africa. :# Start at the Cape of Good Hope. :# Work northward in an orderly manner, traversing the continent alternately east and west, :# During each traverse pass: :#: * Catch each animal seen. :#: * Compare each animal caught to a known elephant. :#: * Stop when a match is detected. This algorithm has a bug, namely a bounds checking error: if no elephants are found, the programmer will continue northwards and end up in the Mediterranean sea, causing abnormal termination. Thus experienced programmers modify the above algorithm by placing a known elephant in Cairo to ensure that the algorithm will terminate. The modified algorithm is therefore as follows: :# Go to Africa. :# Put an elephant in Cairo. :# Start at the Cape of Good Hope. :# Work northward in an orderly manner, traversing the continent alternately east and west, :# During each traverse pass: :#: * Catch each animal seen. :#: * Compare each animal caught to a known elephant. :#: * Stop when a match is detected. :# If you are in Cairo, then there are no elephants in Africa (other than the one you placed there). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Elephant in Cairo」の詳細全文を読む スポンサード リンク
|