Why are there digraphs in C and C++?

Question

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?

Answer 1

I believe that their existence can be traced back to the possibility that somewhere, somebody is using a compiler with an operating system whose character set is so archaic that it doesn't necessarily have all the characters that C or C++ need to express the whole language.

Also, it makes for good entries in the IOCCC.

Answer 2

I think it's because some of the keyboards on this planet might not have keys like '#' and '{'.

Answer 3

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