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
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

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.

-- 
---------------------------------------------------------------------
| John M. Aldrich, aka Fighteer I |     mailto:fighteer AT cs DOT com      |
| Descent 2: The Infinite Abyss - The greatest Internet game of all |
| time just got better!  This time, you're going all the way down...|
---------------------------------------------------------------------