Question

I have a makefile which does what I want with the compilation but I want it also to make a library instead of only object files.

CC=gcc
CFLAGS=-g -Wall
DEPS = tree.h
OBJ = main.o tree.o 

%.o: %.c $(DEPS)
    $(CC) -c -o $@ $< $(CFLAGS)

tree: $(OBJ)
    $(CC) -o $@ $^ $(CFLAGS)

clean:
    rm -f *.o tree

Now I want the makefile to be something like this:

gcc -Wall -g -c tree.c
ar -r libtree.a tree.o
gcc main.c -o main -ltree -L.
./main

What I have to add to my existing makefile?

Answer 1

This should do what you want:

%.o: %.c $(DEPS)
    $(CC) -c -o $@ $< $(CFLAGS)

lib%.a: %.o
    ar -r $@ $^

main: $(OBJ) $(DEPS:%.h=lib%.a)
    $(CC) -o $@ $^ $(CFLAGS) $(DEPS:%.h=-l%) -L.

Note that this only works in GNU Make (in particular, the % in $(DEPS:%.h=lib%.a) is a GNU-specific extension).