Makefile to put object files from source files different directories into a single, separate directory?

Question

I'm using UnitTest++ to allow me to create unit tests for some C++ code (that should build on Linux or Mac OS X). I have a directory structure like this:

src - Foo.cpp - Bar.cpp test - FooTest.cpp - BarTest.cpp - Main.cpp - Makefile UnitTest++ - libUnitTest++.a 

And this Makefile (adapted from the UnitTest++ Makefile) works nicely (with GNU make):

test = TestFooAndBar  src = ../src/Foo.cpp \     ../src/Bar.cpp  test_src = Main.cpp \     FooTest.cpp \     BarTest.cpp  lib = ../UnitTest++/libUnitTest++.a  objects = $(patsubst %.cpp,%.o,$(src)) test_objects = $(patsubst %.cpp,%.o,$(test_src))   .PHONY: all all: $(test)     @echo Running unit tests...     @./$(test)  $(test): $(lib) $(test_objects) $(objects)     @echo Linking $(test)...     @$(CXX) $(LDFLAGS) -o $(test) $(test_objects) $(objects) $(lib)  .PHONY: clean clean:     -@$(RM) -f $(objects) $(test_objects) $(test) 2> /dev/null  %.o : %.cpp     @echo $<     @$(CXX) $(CXXFLAGS) -c $< -o $(patsubst %.cpp,%.o,$<) 

But I want to put all the .o files in an "obj" subdirectory of the "test" directory. How do I modify this Makefile to do so?

I've tried adding "obj/" to the objects and test_objects variables, but I can't figure out how to modify the %.o rule so it knows where the .o files are and refers to the correct .cpp files. Do I need to create two separate rules, one for each set of .cpp files?

Would it be simpler if instead of defining the src and test_src variables, I just have the Makefile build a .o (into obj/) for all .cpp files (both in the same directory as the Makefile and in ../src/)?

Answer 1

There's more than one way to do it, but this is a pretty good one (I really should have that hotkeyed).

vpath %.cpp ../src  src = Foo.cpp Bar.cpp  test_src = Main.cpp FooTest.cpp BarTest.cpp   objects = $(patsubst %.cpp,obj/%.o,$(src))  test_objects = $(patsubst %.cpp,obj/%.o,$(test_src))   $(objects): | obj  obj:   @mkdir -p $@  obj/%.o : %.cpp   @echo $<    @$(CXX) $(CXXFLAGS) -c $< -o $@