Dumb question: What IS a trigraph?

[Doug Gwyn]

In article <3566 at uwovax.uwo.ca> 2014_5001 at uwovax.uwo.ca writes:
>Every so often someone mentions a trigraph.  What is a trigraph???

There's one (the "???").  Standard C requires that, very early in
the phases of translation, certain sequences of three source characters
starting with "??" be mapped into equivalent single characters.  This
is intended to allow C programs to be expressed entirely using the
ISO-646 basic character set, which does not include {, |, and several
other essential C source characters.  It is not expected that real
programming environments would ever require programmers to type these
trigraph sequences; they're intended primarily for program interchange
among different sites.  Unless you're importing a lot of code from
European sites or are implementing a C compiler, you shouldn't have to
be concerned about trigraphs, since you'll never use nor see them.