g++ - how to set up cross-directory dependencies in gnu make -

i've got common set of make rules being used in multiple directories. each make simple:

basedir:=../.. target:=thetarget include makefile.include 

unless overridden, have default value source code:

src:= $(wildcard *.cpp) 

we want build object files in directory (not sources), so:

objdir:= ../obj bare:= $(foreach f,$(src),$(notdir $(f) ) obj:= $(foreach o,$(bare),$(objdir)/$(o).o ) 

so have .o files, need each 1 fire rule based on .cpp long directory known, easy:

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

but in of directories, there arbitrarily grouped files in subdirectories. temporarily got around hardcoding of them in central makefile:

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

but i'd able specify build directories in variable if possible. there way set dependencies

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

and

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

without manually having list out dependencies?

for matter, have dependency files (.d)

$(depdir)/%.d: $(src) 

i want set dependencies based on whatever in source. example: .deps/x.d: a/x.cpp g++ -mm -mt$(objdir)/$(notdir $@) $< -o $(depdir)/$(notdir $@ )

is there easy way generate these rules without writing them each directory?

here's got information on generating .d files in first place: http://mad-scientist.net/make/autodep.html#advanced

the goal in end include .d files , have dependence tree auto-generated files. last part. don't know how use .d files. include them all?

include $(depdir)/%.d 

doesn't work.

i can cat them in rule: cat $(dep) >$(depdir)/deps.inc

and then

include deps.inc 

first, cope source directories:

vpath %.cpp b  $(objdir)/%.o: %.cpp     build... 

then if want can generate dependency files this:

# might use depdir, rather "deps"  $(depdir)/%.d: %.cpp      g++ -mm ...  # note wildcard. , '-' @ beginning means # "don't panic if there aren't any".  -include $(depdir)/*.d 

but there better way described in source cite. don't make rule .d files, build them in same rule builds object files. way don't build them unless need them.