GNU Make pattern to build output in different directory than src

Question

I'm trying to create a Makefile which places my .o files in a different directory than my source files. I'm trying to use a pattern rule so I don't have to create identical rules for each source & object file.

My project structure looks something like:

project/  + Makefile  + src/    + main.cpp    + video.cpp  + Debug/    + src/       [contents built via Makefile:]      + main.o      + video.o 

My Makefile looks something like:

OBJDIR_DEBUG = Debug OBJ_DEBUG = $(OBJDIR_DEBUG)/src/main.o $(OBJDIR_DEBUG)/src/video.o  all: $(OBJ_DEBUG)  $(OBJ_DEBUG): %.o: %.cpp     $(CXX) $(CFLAGS_DEBUG) $(INC_DEBUG) -c $< -o $@ 

This doesn't work, because it looks for my source files at Debug/src/*.cpp.

I've tried the following:

# Broken: make: *** No rule to make target `Debug/src/main.cpp', needed by `Debug/src/main.o'.  Stop. # As a test, works if I change "%.cpp" to "Debug/src/main.cpp", though it obv. builds the wrong thing  # Strip OBJDIR_DEBUG from the start of source files $(OBJ_DEBUG): %.o: $(patsubst $(OBJDIR_DEBUG)/%,%,%.cpp)     $(CXX) $(CFLAGS_DEBUG) $(INC_DEBUG) -c $< -o $@ 

# Broken: #   Makefile:70: target `src/main.o' doesn't match the target pattern #   Makefile:70: target `src/video.o' doesn't match the target pattern  # Add OBJDIR_DEBUG in target rule OBJ = src/main.o src/video.o  $(OBJ): $(OBJDIR_DEBUG)/%.o: %.cpp     $(CXX) $(CFLAGS_DEBUG) $(INC_DEBUG) -c $< -o $@ 

Answer 1

After re-reading the documentation on static pattern rules, I derived the following pattern rule which seems to work.

$(OBJ_DEBUG): $(OBJDIR_DEBUG)/%.o: %.cpp     $(CXX) $(CFLAGS_DEBUG) $(INC_DEBUG) -c $< -o $@ 

I'm not sure this is the best approach, and I'm open to suggestions.