Xref: news2.mv.net comp.os.msdos.djgpp:2727
From: Broeker AT axp03 DOT physik DOT rwth-aachen DOT de (Hans-Bernhard Broeker)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: problems with makefiles
Date: 15 Apr 96 12:39:32 GMT
Organization: RWTH -Aachen / Rechnerbetrieb Informatik
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Message-ID: <Broeker.829571972@axp03>
References: <Pine DOT SOL DOT 3 DOT 91 DOT 960415004409 DOT 22714A-100000 AT sauron>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

"Rafael R. Sevilla" <rsevilla AT upd DOT edu DOT ph> writes:

>Hi. I've been using Bison for some time to build a small language, and it
>appears to give me lots of problems in conjunction with make. In order to
>make my lang.c file for example, my makefile has the following lines

>lang.c lang_tab.h: lang.y $(HEADERS)
^^^^^^^^^^^^^^^^^^^
That's the source of your problem. (Explained below)
>	bison -y -d lang.y
>	update y_tab.c lang.c
>	update y_tab.h lang_tab.h

>lang.o: lang.c

>	...

>Trouble is, make does a lot of redundant work: it runs bison twice and
>consequently recompiles lang.c twice too, for some reason that escapes me.
>Make was invented in order to avoid redundant compiles, but it appears to 
>be adding to them here. What's going on? Is there something wrong with my 
>makefile?

Yes, as pointed out above, there is something wrong: in a nutshell, you
should *never* have make build more than one file per rule. In the
case given above, I think this should be changed to something like:

y_tab.c: lang.y $(HEADERS)
	bison -y -d lang.y
lang_tab.h: y_tab.c
	update y_tab.h lang_tab.h
lang.c: y_tab.c
	update y_tab.c lang.c

As to the use of update vs. copy/cp, I'm not really sure it is a
good choice here, but you'll find out about that yourself soon
enought, I guess.

And, as Eli already pointed out, using the default .y.c make rules
(with YACC=bison -y) might be a good idea as well

Hans-Bernhard Broeker (Aachen, Germany)