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I learned today that there are digraphs in C99 and C++. The following is a valid program:
%:include <stdio.h> %:ifndef BUFSIZE %:define BUFSIZE 512 %:endif void copy(char d<::>, const char s<::>, int len) <% while (len-- >= 0) <% d<:len:> = s<:len:>; %> %> My question is: why do they exist?
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C Language Multi-Character Character Sequence Digraphs These use only two characters and are known as digraphs. Unlike trigraphs, digraphs are tokens. If a digraph occurs in another token (e.g. string literals or character constants) then it will not be treated as a digraph, but remain as it is.
Trigraph sequences allow C programs to be written using only the ISO (International Standards Organization) Invariant Code Set. Trigraphs are sequences of three characters (introduced by two consecutive question marks) that the compiler replaces with their corresponding punctuation 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.
The C programming language doesn't seem to have an expiration date. It's closeness to the hardware, great portability and deterministic usage of resources makes it ideal for low level development for such things as operating system kernels and embedded software.
Digraphs were created for programmers that didn't have a keyboard which supported the ISO 646 character set.
http://en.wikipedia.org/wiki/C_trigraph
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