Re: C preprocessor vs Macro processor

Peter Govoni <peter.govoni@analog.com> writes:


> Could someone please explain why a macro processor (e.g. M4)
> is 1) more powerful than the C preprocessor and


M4 allows rearranging code too. e.g., you can have a macro that takes
part of its arguments and writes them out to a diverted channel, and
then later output that previously-hidden channel. Cpp allows only
local expansion of macros.


Also, M4 has many many more builtin functions (including regular
expression matching, and much more) and permits recursive macros; Ansi
C's cpp disallows recursion in macros.


M4 also permits a macro's expansion to include a newline; cpp cannot
(hence the imake hack of replacing @@ w/ newlines after the
preprocessor has run).


> 2) more suitable for assembly languages


Perhaps because M4 is more powerful; you can build more infrastructure
more easily w/ M4, raising the level of abstraction more easily --
something assembly truly benefits from.


> Does the C preprocessor hold any advantage over M4 ?


It's easier to learn, is not stuck with complicated quoting rules, and
more constrained in its capabilities; reasoning about source code
preprocessed by cpp is hard enough -- reasoning about source code
processed by m4 would be nearly impossible.


Greg J. Badros
gjb@cs.washington.edu
Seattle, WA USA
http://www.cs.washington.edu/homes/gjb




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