C++ Trigraphs – Are Trigraphs Still Valid in C++?

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

From the first ISO C++ standard C++98, this is described in 2.5/ Alternative tokens [lex.digraph]:

1. Alternative token representations are provided for some operators and punctuators.
2. In all respects of the language, each alternative token behaves the same, respectively, as its primary token, except for its spelling. The set of alternative tokens is defined in Table 2.

Table 2 - Alternative tokens

    alternative primary | alternative primary | alternative primary
    --------------------+---------------------+--------------------
       <%          {    |    and         &&   |    and_eq      &=
       %>          }    |    bitor       |    |    or_eq       |=
       <:          [    |    or          ||   |    xor_eq      ^=
       :>          ]    |    xor         ^    |    not         !
       %:          #    |    compl       ~    |    not_eq      !=
       %:%:        ##   |    bitand      &    |

So it's been around since the earliest days of the C++ standardisation process. The reason so few people are aware of it is likely because the main use case was for people operating in environments where the full character set wasn't necessarily available. For example (and this is stretching my memory), the baseline EBCDIC character set on the IBM mainframes did not have the square bracket characters [ and ].