I have a question about preprocessor behavior:

--- example ---

void ab() { // test function
    return;
}

#define CONCAT_1(A, B) A ## B
#define CONCAT_2(A, B) CONCAT_1(A, B)

#define DELAY(NAME) NAME

#define A1 a
#define B1 b

#define A2() a
#define B2() b

#define LHS (
#define RHS )

int main() {
    DELAY(CONCAT_1)(A1, B1)();
    DELAY(CONCAT_1) LHS A1, B1 RHS ();
    CONCAT_1 ( a, b ) ();
    DELAY(CONCAT_1)(A2(), B2())();
    DELAY(CONCAT_2)(A1, B1)();
    return 0;
}

--- end example ---

I would expect all of the above lines to expand to the same thing, i.e.
'ab()' five times.
I preprocessed this file with Comeau C++, Borland BCC55, VC++6, and VC++7;
here are my results:

Comeau -and- Borland both produced the following (for the macro expansion
section of the 'code' above):

A1B1();
CONCAT_1 ( a, b ) ();
ab();
a b();
ab();

Both versions of Visual C++ produced the following:

A1B1();
CONCAT_1 ( a, b ) ();
ab();
ab();
ab();

Which is correct?  It wouldn't surprise me if they are all wrong.  For
instance, why doesn't rescanning pick up CONCAT_1 produced by the second
line--it is exactly equivalent to the original line 3.  Also, what is the
difference between line 1 and line 4 (i.e. function-like macro vs. no-arg
macro)?--yet in all four preprocessors it produces a different output.  Why
does using CONCAT_2 make a difference in the last line since it simply
delegates its parameters to CONCAT_1?

This is what I expected:

// after 1st pass

CONCAT_1 ( a , b ) ();
CONCAT_1 ( a , b ) ();
ab();
CONCAT_1 ( a , b ) ();
CONCAT_2 ( a , b ) ();

// after 2nd pass

ab();
ab();
ab();
ab();
CONCAT_1(a, b) ();

// after 3rd pass

ab();
ab();
ab();
ab();
ab();

Where am I going wrong, or conversly where are these preprocessors going
wrong?

Thanks for the help,
Paul Mensonides

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