Flat object file directory structure output with GNU Make

Question

I have a C++ small project using GNU Make. I\'d like to be able to turn the following source files:

src/
  a.cpp
  b/
    b.cpp
  c/
    c.cpp

Answer 1

Creating the flat directory structure as initially requested.

Does use vpath to track down the source files, but all the bookeeping is done automagically from the SRC list.

SRC = a/a.c a/aa.c b/b.c
TARGET = done

FILES = $(notdir $(SRC) )
#make list of source paths, sort also removes duplicates
PATHS = $(sort $(dir $(SRC) ) )

BUILD_DIR = build
OBJ = $(addprefix $(BUILD_DIR)/, $(FILES:.c=.o))
DEP = $(OBJ:.o=.d)

# default target before includes
all: $(TARGET)

include $(DEP)

vpath %.c $(PATHS)

# create dummy dependency files to bootstrap the process
%.d:
    echo a=1 >$@

$(BUILD_DIR)/%.o:%.c
    echo $@: $< > $(patsubst %.o,%.d,$@)
    echo $< >$@

$(TARGET): $(OBJ)
    echo $^ > $@

.PHONY: clean
clean:
    del $(BUILD_DIR)/*.o
    del $(BUILD_DIR)/*.d

Sorry about the ugly echo's but I only had my win box to test it on.