Trigraph

Trigraph may refer to:

Computing

Cryptography

Mathematics

Other uses

Digraphs and trigraphs

In computer programming, digraphs and trigraphs are sequences of two and three characters, respectively, that appear in source code and, according to a programming language specification, should be treated as if they were single characters.

Various reasons exist for using digraphs and trigraphs: keyboards may not have keys to cover the entire character set of the language, input of special characters may be difficult, text editors may reserve some characters for special use and so on. Trigraphs might also be used for some EBCDIC code pages that lack characters such as { and }.

History

The basic character set of the C programming language is a subset of the ASCII character set that includes nine characters which lie outside the ISO 646 invariant character set. This can pose a problem for writing source code when the encoding (and possibly keyboard) being used does not support any of these nine characters. The ANSI C committee invented trigraphs as a way of entering source code using keyboards that support any version of the ISO 646 character set.

Trigraph (orthography)

A trigraph (from the Greek: τρεῖς, treîs, "three" and γράφω, gráphō, "write") is a group of three letters used to represent a single sound or a combination of sounds that does not correspond to the written letters combined.

Latin-script trigraphs

For example, in the word schilling, the trigraph sch represents the voiceless postalveolar fricative /ʃ/, rather than the consonant cluster */skh/. In the word beautiful, the sequence eau is pronounced /juː/, and in the French word château it is pronounced /o/. It is sometimes difficult to determine whether a sequence of letters in English is a trigraph, because of the complicating role of silent letters. There are few productive trigraphs in English such as tch as in watch, and igh as in high.

The trigraph sch in German is equivalent to the English sh and pronounced ʃ. In the Dutch language, which is closely related to German, this same trigraph is pronounced sx. In neither language is this trigraph regarded as an independent letter of the alphabet. In Hungarian, the trigraph dzs is treated as a distinct letter, with its own place in the alphabet. It is pronounced like an English "j" /dʒ/. The combination gli in Italian can also be a trigraph, representing the palatal lateral approximant /ʎ/ before vowels other than i.