Re: how can I do this in gmake?

[ma]

"Maxim Yegorushkin" <address@hidden> wrote in message 
news:address@hidden
> ma wrote:
>
>> I am writing a make file that will be used on several development. in 
>> each
>> development, there are a huge amount of file that needed to be built but
>> only a small part of them is changing and others are  not changing. I put
>> all of these files into a library. The idea is that when the user run 
>> make
>> file for the first time, it will create all of the source files and then
>> create library and copy somewhere in the system. On any other call to 
>> this
>> make file (maybe from some other directory that doesn't have  *.obj files
>> related to library in it), it checks if the lib exist, use it and if not
>> create it.
>
> This may help you:
>
> address@hidden tmp]$ cat Makefile
> all :
>
> libmy_obj := a.o b.o
> lib/libmy.a : $(libmy_obj) | lib
>
> foo_obj := foo.o
> bin/foo : $(foo_obj) lib/libmy.a | bin
> bin/foo : LDFLAGS += -Llib -lmy
>
> bar_obj := bar.o
> bin/bar : $(bar_obj) lib/libmy.a | bin
> bin/bar : LDFLAGS += -Llib -lmy
>
> bin/% :
> $(CC) -o $@ $($(@F)_obj) $(LDFLAGS)
>
> lib/% :
> ar r $@ $($(@F)_obj)
>
> .PHONY : all clean
>
> all : lib/libmy.a bin/foo bin/bar
>
> lib bin :
> mkdir -p $@
>
> clean :
> rm -rf *.{c,o} lib bin
>
> # create dummy source files
> a.c b.c :
> touch $@
> %.c :
> echo "int main() {}" > $@
>
> address@hidden tmp]$ make
> touch a.c
> cc    -c -o a.o a.c
> touch b.c
> cc    -c -o b.o b.c
> mkdir -p lib
> ar r lib/libmy.a
> ar: creating lib/libmy.a
> echo "int main() {}" > foo.c
> cc    -c -o foo.o foo.c
> mkdir -p bin
> cc -o bin/foo foo.o -Llib -lmy
> echo "int main() {}" > bar.c
> cc    -c -o bar.o bar.c
> cc -o bin/bar bar.o -Llib -lmy
> rm bar.c foo.c
> address@hidden tmp]$ make bin/foo
> make: `bin/foo' is up to date.
> address@hidden tmp]$ rm lib/libmy.a
> address@hidden tmp]$ make bin/foo
> ar r lib/libmy.a
> ar: creating lib/libmy.a
> cc -o bin/foo foo.o -Llib -lmy

Thanks.
I belive the main trick that used here is

lib/libmy.a : $(libmy_obj) | lib

which I think telling that if lib is uptodate, don't go for $(libmy_obj) 
prerequiatic else go and use that pre requistic. Am I wring?

regards