Re: #define and (brackets)

"Alan Carre" <alan@xxxxxxxxxxxxxxxxx> wrote in message
news:OoQb5opTJHA.5860@xxxxxxxxxxxxxxxxxxxx
"Igor Tandetnik" <itandetnik@xxxxxxxx> wrote in message
news:epMGpUoTJHA.3520@xxxxxxxxxxxxxxxxxxxxxxx
Alan Carre <alan@xxxxxxxxxxxxxxxxx> wrote:
-SHRINK_BOX_AMOUNT won't get parsed as --20, but as - -20 (which will
likely compile just fine, but I'm too lazy to check). Preprocessor
works after lexer, handling tokens rather than individual
characters. You need ## operator to create new tokens.


Nope, just try it. It won't compile, no spaces are inserted after the
minus sign.

This program successfully compiles:

#define X -1

int main()
{
return -X;
}

And --20 is not a *new* token, it is not a token at all!

--20 is parsed as two tokens, "--" and "20". -X in the above example
gets expanded to three tokens, "-", "-" and "1". Compiler proper works
on a stream of tokens (after lexer and preprocessor), not a stream of
characters. For more details, see C++ standard 2.1 "Phases of
translation".
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925


.

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