idempotent adj.
[from mathematical techspeak] Acting as if used only once,
even if used multiple times. This term is often used with respect
to C header files, which contain common
definitions and declarations to be included by several source
files. If a header file is ever included twice during the same
compilation (perhaps due to nested #include files), compilation
errors can result unless the header file has protected itself
against multiple inclusion; a header file so protected is said to
be idempotent. The term can also be used to describe an
initialization subroutine that is arranged to perform some
critical action exactly once, even if the routine is called
several times.
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IDP /I-D-P/ v.,n.
[Usenet] Abbreviation for Internet Death Penalty.
Common (probably now more so than the full form), and frequently
verbed. Compare UDP.
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If you want X, you know where to find it.
There is a legend that Dennis Ritchie, inventor of C, once responded to demands for features resembling
those of what at the time was a much more popular language by
observing "If you want PL/I, you know where to find it." Ever
since, this has been hackish standard form for fending off
requests to alter a new design to mimic some older (and, by
implication, inferior and baroque)
one. The case X = Pascal manifests
semi-regularly on Usenet's _comp.lang.c_ newsgroup. Indeed,
the case X = X has been reported in discussions of graphics
software (see X).
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ifdef out /if'def owt/ v.
Syn. for condition out,
specific to C.