How to Compile Object files into an Archive using Make - c

Question

Problem
I'm writing a B-tree in c and it's getting pretty big. I have a struct for the tree, one for the nodes, and one for the items (key/value). I'd like to compile the object files from all three header files into an archive (.a) using make. Whenever I try to compile using make it uses the archive without every building the objects. Any idea why?
include/
btree.h
item.h
node.h
src/
btree_attach.c
btree_create.c
btree_destructor.c
btree_disk.c
btree_find.c
btree_get_node.c
btree_insert.c
btree_key_size.c
item_compare_item.c
item_compare_item_qsort.c
item_print_item.c
node_create_.c
node_destructor.c
node_find.c
node_flush_node.c
node_insert.c
node_print_node.c
node_split_node.c
# Generic makefile
# VAriables:
src := $(wildcard *.c)
obj := $(obj:.c=.o)
dep := $(dep:.o=.d)
CFLAGS := -g
INCLUDE = -Iinclude
all: lib/btree.a\
clean:
rm -f a.out obj/* bin/*
# ---------------
# Object files
$(obj): $(src) $(dep)
$(CC) $(CFLAGS) $(INCLUDE) $# $^
#Archive file
.PHONY: lib/btree.a
lib/btree.a: $(obj) $(dep)
ar -rv $# $^
Update
I changed the make file to the following:
# VAriables:
src := $(wildcard src/*.c)
obj := $(src:.c=.o)
dep := $(obj:.o=.d)
CFLAGS := -g
INCLUDE = -include
print:
$(src)\
$(obj)\
$(dep)
all: lib/btree.a
# ---------------
# Object files
$(obj): $(src)
$(CC) $(CFLAGS) $(INCLUDE) $# $^
#Archive file
lib/btree.a: $(obj)
ar -rv $# $^
The printout has the following
src/b_util.c src/item_compare_item.c src/b_tree.c src/item_print_item.c src/random_tester_2.c src/node_attach.c src/node_find.c src/node_create_.c src/btree_disk.c src/node_insert.c src/tnode.c src/btree_create.c src/node_unattach.c src/b_tree_test.c src/node_split_node.c src/node_print_node.c src/random_tester_1.c src/node_destructor.c src/btree_insert.c src/item.c src/btree_attach.c src/item_compare_item_qsort.c src/node_flush_node.c src/jdisk.c src/btree_find.c src/btree_destructor.c src/btree_get_node.c src/jdisk_test.c src/btree_key_size.c\
src/b_util.o src/item_compare_item.o src/b_tree.o src/item_print_item.o src/random_tester_2.o src/node_attach.o src/node_find.o src/node_create_.o src/btree_disk.o src/node_insert.o src/tnode.o src/btree_create.o src/node_unattach.o src/b_tree_test.o src/node_split_node.o src/node_print_node.o src/random_tester_1.o src/node_destructor.o src/btree_insert.o src/item.o src/btree_attach.o src/item_compare_item_qsort.o src/node_flush_node.o src/jdisk.o src/btree_find.o src/btree_destructor.o src/btree_get_node.o src/jdisk_test.o src/btree_key_size.o\
src/b_util.d src/item_compare_item.d src/b_tree.d src/item_print_item.d src/random_tester_2.d src/node_attach.d src/node_find.d src/node_create_.d src/btree_disk.d src/node_insert.d src/tnode.d src/btree_create.d src/node_unattach.d src/b_tree_test.d src/node_split_node.d src/node_print_node.d src/random_tester_1.d src/node_destructor.d src/btree_insert.d src/item.d src/btree_attach.d src/item_compare_item_qsort.d src/node_flush_node.d src/jdisk.d src/btree_find.d src/btree_destructor.d src/btree_get_node.d src/jdisk_test.d src/btree_key_size.d
Essentially they all went to the src dir but I'd like them to be seperated into (see below). Why is it putting everything in src?
obj/*.o
dep/*.d
src/*.c

Answer 1

Most likely because your sources variable src is empty. Which means your objects list variable obj is empty. Which means that your library lib/btree.a doesn't depend on anything, so make doesn't build anything.
This is most likely because this:
src := $(wildcard *.c)
obj := $(obj:.c=.o)
dep := $(dep:.o=.d)
should instead be:
src := $(wildcard src/*.c)
obj := $(src:.c=.o)
dep := $(obj:.o=.d)
It would be more clear if you showed us where your makefile was, and what directory you invoking make from.
You have a lot of other issues as well; for example this:
$(obj): $(src) $(dep)
$(CC) $(CFLAGS) $(INCLUDE) $# $^
is quite wrong. This says "each object file depends on ALL the source files and ALL the dependency files", and "to build a single object file, you compile ALL the source files".