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In computing, idempotence (IPA [ˈaɪdɛmˌpotns/, like eye-dem-potence) is the quality of something that has the same effect if used multiple times as it does if used only once, similarly to the idempotence notion in mathematics. Originally, the word computing was synonymous with counting and calculating, and a science that deals with the original sense of computing mathematical calculations. ...
The International Phonetic Alphabet (IPA) is a system of phonetic notation devised by linguists to accurately and uniquely represent each of the wide variety of sounds (phones or phonemes) used in spoken human language. ...
There are two main definitions of idempotence (IPA , like eye-dem-potent-s) in mathematics. ...
Euclid, detail from The School of Athens by Raphael. ...
Idempotent operation means that it can be repeated without causing any errors or inconsistencies if the operation is carried out once or many times.
Idempotent header files
C header files are often designed to be idempotent, that is, if the header file is included more than once (as can easily happen with nested #included files), then nothing untoward happens - the effect is the same as if a file had been included only once. The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a general-purpose, procedural, imperative computer programming language developed in the early 1970s by Dennis Ritchie for use on the UNIX...
In computer programming, especially in the C programming language or C++, a header file is a text file containing small bits of program code, which is used to describe the contents of the main body of code to other modules. ...
A standard trick is to surround the whole text of the includable file by #ifndef/#endif directives:
/* File: sample_header.h */ #ifndef UNIQUE_PREPROCESSOR_CONSTANT #define UNIQUE_PREPROCESSOR_CONSTANT /* Here goes the material content of the file */ #endif
WWW behavior HTTP GET requests are defined to be idempotent. The web infrastructure makes this assumption and often caches the result of these requests. Error creating thumbnail: convert: unable to open image `/mnt/upload3/wikipedia/commons/d/d1/First_Web_Server. ...
This article is about the computer term. ...
Incorrect programming of a web site may sometimes lead to undesired behavior. In some cases, usually an incorrect or missing timestamp, the software cannot correctly detect that the content of the requested page has been changed since the last request. If there is a suspicion of this happening, the local cache may need to be cleared.
HTTP POST requests (usually used for user input forms) are not meant to be idempotent, so the result of a POST request is not cached.
User interface In user interface design, a button is "idempotent" if pressing it more than once will have the same effect as pressing it once. For example, a "Pause" button is not idempotent if it toggles the paused state. On the other hand, if pressing it multiple times keeps the system paused and pressing "Play", a different button, resumes, then "Pause" is idempotent. This is useful in interfaces such as infrared remote controls and touch screens where the user may not be sure of having pressed the button successfully and may press it again. Elevator call buttons are also idempotent (until the called elevator has arrived and redeparted), though some people behave as though they are not. The user interface is the part of a system exposed to users. ...
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