Question

I’ve got a common set of make rules being used in multiple directories. Each make is very simple:

BASEDIR:=../..
TARGET:=theTarget
include Makefile.include

Unless overridden, I have a default value for the source code:

SRC:= $(wildcard *.cpp)

We want to build the object files in a directory (not with the sources), so:

OBJDIR:= ../obj
BARE:= $(foreach f,$(SRC),$(notdir $(f) )
OBJ:= $(foreach o,$(BARE),$(OBJDIR)/$(o).o )

So I have the .o files, but I need each one to fire a rule based on the .cpp
As long as the directory is known, this is easy:

$(OBJDIR)/%.o: %.cpp

but in some of the directories, there are arbitrarily grouped files in subdirectories. I temporarily got around this by hardcoding all of them in my central makefile:

$(OBJDIR)/%.o: a/%.cpp
    build...
$(OBJDIR)/%.o: b/%.cpp
    build...

But what I’d like to do is be able to specify the build directories in a variable if possible. Is there any way to set up the dependencies

$(OBJDIR)/x.o: a/x.cpp
$(OBJDIR)/y.o: a/y.cpp

and

$(OBJDIR)/z.o: b/z.cpp

without manually having to list out the dependencies?

For that matter, I also have dependency files (.d)

$(DEPDIR)/%.d: $(SRC)

I want to set up dependencies based on whatever is in the source.
For example:
.deps/x.d: a/x.cpp
g++ -MM -MT$(objdir)/$(notdir $@) $< -o $(DEPDIR)/$(notdir $@ )

Is there an easy way to generate these rules without writing them for each directory?

Here’s where I got the information on generating the .d files in the first place:
http://mad-scientist.net/make/autodep.html#advanced

The goal in the end is to include all the .d files and have dependence tree auto-generated from the files. But that is the last part. I don’t know how to use the .d files. Do I just include them all?

include $(DEPDIR)/%.d

doesn’t work.

I can cat them all together in a rule:
cat $(DEP) >$(DEPDIR)/deps.inc

and then

include deps.inc

Answer 1

First, to cope with the source directories:

vpath %.cpp a b

$(OBJDIR)/%.o: %.cpp
    build...

Then if you want you can generate the dependency files like this:

# Might as well use DEPDIR, rather than "deps"

$(DEPDIR)/%.d: %.cpp 
    g++ -MM ...

# Note the wildcard. And the '-' at the beginning means
# "don't panic if there aren't any".

-include $(DEPDIR)/*.d

But there is a better way which is described in the source you cite. Don’t make a rule for the .d files, just build them in the same rule that builds the object files. That way you don’t build them unless you actually need them.