Nonrecursive Multilevel makefile - makefile

Question

I am starting to work on a project that I would like to grow to be fairly large. I Want to create a makefile that will grow with the project without much maintenance. Here is the directory structure that I have right now.
.
+--src
| +--part1
| | +--part1.c
| | +--part1.h
| +--part2
| | +--part2.c
| | +--part2.h
. .
. .
. .
| +--partN
| | +--partN.c
| | +--partN.h
+--test
| +--part1_tests
| | +--part1_testX.c
| | +--part1_testY.c
. .
. .
. .
+--obj
| +--part1.o
| +--part2.o
. .
. .
. .
| +--partN.o
+--a.out
I have never had a project of this scale and never needed to make a make file for such a project. How would I design a makefile for this? Thanks!

Answer 1

There are different ways to do it, but i would start by not letting the makefile grow with the project. Instead I would use the regular structure to define rules to handle projects with one codefile in one directory, to big projects with thousend of files.
For example lets play a little bit with your structure (not tested might have some typos and I assume that you start make from project dir):
# we nead the header directory
INCDIRS = src
# collect every cpp file
CXXSRCS = $(shell find src/ -type f -name '*.cpp' 2>/dev/null)
# now generate the object file names
OBJSTMP = $(CXXSRCS:%.cpp=obj/%.o)
# compiled the source file
obj/%.o: src/%.cpp
$(CXX) ${CXXFLAGS} $(foreach bin,${INCDIRS},-I${bin}) -o "$#" "$<"
now lets say your main is in part1.cpp:
ifneq (,$(wildcard src/part1/part1.cpp))
# I just dont like a.out...
executable=${APPLICATION_NAME}
# now lets build the exe:
${executable}: ${OBJS}
$(LD) $(LDFLAGS) -o $# $^
endif
now the last thing is a little cosmetic:
.PHONY: clean all
all: install
compile: ${OBJS}
package: compile ${executable}
#now we can move the object files to were they should be
mv -f obj/part*/* obj/
install: package
no matter how big your project is gonna be this makefile will do some of your steps. Its just to give your an idea. I ignored the test_files. But thinking ahead you can collect the test sources in the same way like I did with the normal sources.
So my point is, there is absolutely no reason why your makefile has to grow with the size of your project, only with its complexity.
For more information, look in the Documentation here at stackoverflow, there is plenty information for makefiles...
Hope that helps,
Kai