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c++ansi-c

Why are there alternative tokens in C++?

Possible Duplicate:
Why are there digraphs in C and C++?
What does the C ??!??! operator do?!

In C++ there are alternative tokens for [] and {}, among others.

E.g. the following code compiles:

%:include <stdio.h>
int main() <%
    printf("Hello World!");
}

I thought about it for a while but couldn't figure any applicability, is there any logical reason for this?

Solution

  • They're a hangover from C, really. There were implementations of C in which not all characters were available (such as some variants of EBCDIC that have no square brackets).

    The C99 rationale document, section 5.2.1.1 Trigraph sequences has this to say:

    Trigraph sequences were introduced in C89 as alternate spellings of some characters to allow the implementation of C in character sets which do not provide a sufficient number of non-alphabetic graphics.

    The characters in the ASCII repertoire used by C and absent from the ISO/IEC 646 invariant repertoire are #, [, ], {, }, \, |, ~, and ^