From:	"John M. Aldrich" <fighteer AT cs DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Using `make' to maintain libraries
Date:	Fri, 20 Jun 1997 19:31:30 +0000
Organization:	Two pounds of chaos and a pinch of salt
Lines:	60
Message-ID:	<33AADA92.5888@cs.com>
References:	<199706201650 DOT JAA09741 AT adit DOT ap DOT net>
Reply-To:	fighteer AT cs DOT com
NNTP-Posting-Host:	ppp102.cs.com
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Nate Eldredge wrote:
> 
> Does anyone know of a way to have `make' rebuild only the changed members of
> a .a library? For example, I have a library libfoo.a containing func1.o,
> func2.o ... func(n).o. Each .o member is built from a .c source. The easy
> way is to do this:
> --cut--
> OBJS = func1.o func2.o [...] func(n).o
> 
> libfoo.a : libfoo.a($(OBJS))
> --cut--
> and let implicit rules handle the rest. This is described in the Archives
> section of the docs. But what happens when I make is, if the library is not
> up-to-date, every source file is recompiled, and every member re-inserted.
> This can take a loooong time if `n' is large.
> 
> So what I want is:
> for (each source file newer than libfoo.a) do
>         compile source file
>                 gcc -o funcx.o funcx.c
>         re-insert member
>                 ar -r libfoo.a funcx.c
> 
> How do I get `make' to do this? Is it even possible?

There are two ways that I can think of.

Method 1:

OBJS = func1.o func2.o [...] func(n).o

libfoo.a : $(OBJS)

%.o : %.c
	$(CC) -c $(CFLAGS) $<
        $(AR) rs libfoo.a $@

This has the advantage of doing exactly what you want, but it would take
a long time if several source files were updated.  A faster way would
be...

Method 2:

OBJS = func1.o func2.o [...] func(n).o

libfoo.a : $(OBJS)
	$(AR) rs $@ $^

This compiles only the necessary library members and then rebuilds the
entire library.

I don't know why make isn't working right when you use the archive
member format to specify dependencies.

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