How to make G++ preprocessor output a newline in a macro?

Is there a way in gcc/g++ 4.* to write a macro that expands into several lines?

The following code:

#define A X \ Y

Expands into

X Y

I need a macro expanding into

X
Y

Got it!

#define anlb /*
*/ A /*
*/ B

anlb anlb

gcc -E -CC nl.c

/*
*/ A /*
*/ B /*
*/ A /*
*/ B

Make the macro generate a special markup, say __CR__, then pipe the result of CPP into a script which translates the macro to a true newline, for example, sed 's/__CR__/\n/g'.

I just found this useful to generate a code pattern to be filled by hand. It is quite easier when the code is readable.

You can just put a magic character sequence in the macro, e.g.

#define X(y,z) y nl z

run gcc -E infile | sed g/s/nl/\n/ > whatever

(Maybe not exactly right, but you get the idea, right? Pipe it through sed or tr or run Emacs on the output.)

I do this sometimes to use C macros to generate source code and no I don't want to learn how to do it in Perl or M4 or yet another tool.

Putting a side the fact that not being able to put newlines in macros create unreadable code, making it harder to debug preprocessor outputs. It is true that C and C++ might not care about newlines, but the C preprocessor does.

I would really like to make a macro ConditionalDefine(x,y) that outputs the following.

    #ifdef x
    #define y
    #endif

The following defines do something close:

    #define hash #
    #define nl
    #define _def_p8(A,B) A ifdef _P8_K60_BOARD_ A define B  A endif
    #define X_def_p8(A,B) _def_p8(A,B)
    #define def_p8(A) X_def_p8(nl hash,A)

expanding the following:

    def_p8(PTPD_DBGA 0)

results in:

    # ifdef _P8_K60_BOARD_ # define PTPD_DBGA 0    # endif

But without being able to put new lines in before the hashes it would not work as intended. It is also annoying the hoops you have to jump through just to get that close.

I'm pretty sure CPP, being designed for C which doesn't care for newlines, and all, can't handle this kind of work. Still you can mark wanted newlines with some special marker string and pass the result through sed or awk to get what you want.