Makefile with generic intermediate rules - makefile

Question

I have a makefile that works that looks like this:
TARGET:=prog
SOURCES:=a.c b.c
CFLAGS:=-Wall -g -O2
OBJECTS:=$(SOURCES:%.c=%.o)
$(TARGET): $(OBJECTS)
gcc -o $# $^
%.o: %.c
gcc $(CFLAGS) -c -o $# $<
clean:
rm -f $(TARGET) $(OBJECTS)
The only variables that the user needs to change are the target name and the sources required to build it. The objects that need to be generated are automatically determined from the sources. I would like to extend this to support multiple targets, each with its own list of sources. I'm having trouble getting the syntax right, though. This is the general idea:
TARGETS:=prog1 prog2
SOURCES_prog1:=a.c b.c
SOURCES_prog2:=a.c c.c
CFLAGS:=-Wall -g -O2
OBJECTS_$#=$(SOURCES_$#:%.c=%.o)
$(TARGETS): $(OBJECTS_$#)
gcc -o $# $^
%.o: %.c
gcc $(CFLAGS) -c -o $# $<
clean:
rm -f $(TARGET) $(OBJECTS)
But I can't get the object list to be generated correctly. I'm also unsure how to write the clean rule to clean all of the objects. Is this possible?

Answer 1

There are two primary ways that I see to do this.
The first involves dynamically creating the target/prerequisite mappings using the $(eval) function.
TARGETS:=prog1 prog2
SOURCES_prog1:=a.c b.c
SOURCES_prog2:=a.c c.c
CFLAGS:=-Wall -g -O2
$(TARGETS):
gcc -o $# $^
$(foreach t,$(TARGETS),$(eval OBJECTS_$t := $(SOURCES_$t:.c=.o))$(eval $t: $(OBJECTS_$t)))
The second involves using Secondary Expansion.
TARGETS:=prog1 prog2
SOURCES_prog1:=a.c b.c
SOURCES_prog2:=a.c c.c
CFLAGS:=-Wall -g -O2
.SECONDEXPANSION:
$(TARGETS): $$(OBJECTS_$$#)
gcc -o $# $^
$(foreach t,$(TARGETS),$(eval OBJECTS_$t := $(SOURCES_$t:.c=.o)))
In either case the clean target becomes:
clean:
rm -f $(TARGETS) $(foreach t,$(TARGETS),$(OBJECTS_$t))