How to compile a c++ project with multiple directories using Makefiles? - c++

Question

I have read other questions asking similar things, alas I am still confused.
This is my current Makefile:
CC = g++
EXEFILE = template
IFLAGS= -I/usr/include/freetype2 -I../Camera
LFLAGS= -L/usr/lib/nvidia-375 -L/usr/local/lib -L/usr/include/GL -L/usr/local/include/freetype2 -L/usr/local/lib/
LIBS = -lglfw -lGL -lGLU -lOpenGL -lGLEW -pthread -lfreetype
SRC=*.cpp
DEPS=*.h
$(EXEFILE):
$(CC) -std=c++11 -o $(EXEFILE) -Wall -Wno-comment $(SRC) $(IFLAGS) $(LFLAGS) $(LIBS)
all: run clean
run: $(EXEFILE)
./$(EXEFILE)
clean:
rm $(EXEFILE)
Right now all of my .h files and .cpp files are on the working directory, and everything compiles and runs just fine. My issue is that I have already a large number of files, and it is getting quite messy. I want to create multiple directories (and maybe even directories inside these directories) to organize my files. But as soon as I move a header file and it's corresponding cpp file(s) to a directory inside of the current directory the compiler doesn't know how to link them anymore.
How do I tell my make file to compile and link everything under the current root?
Alternatively, is there a ELI5 guide to makefile syntax?

Answer 1

The quickest way to solve your problem is to add SRC and DEPS the files contains in all your sub-directories, something like:
SRC=*.cpp src/*.cpp
DEPS=*.h inc/*.h
Now you may consider writing a rule to first compile every file in a separate directory:
# Group compilation option
CXXFLAGS := -std=c++11 -Wall -Wno-comment $(IFLAGS)
# A directory to store object files (.o)
ODIR := ./objects
# Read this ugly line from the end:
# - grep all the .cpp files in SRC with wildcard
# - add the prefix $(ODIR) to all the file names with addprefix
# - replace .cpp in .o with patsubst
OBJS := $(patsubst %.cpp,%.o,$(addprefix $(ODIR)/,$(wildcard $(SRC)/*.cpp)))
# Compile all the files in object files
# $# refers to the rule name, here $(ODIR)/the_current_file.o
# $< refers to first prerequisite, here $(SRC)/the_current_file.cpp
$(ODIR)/%.o:$(SRC)/%.cpp $(DEPS)/%.h
$(CXX) $(CXXFLAGS) -c -o $# $<
# Finally link everything in the executable
# $^ refers to ALL the prerequisites
$(EXEFILE): $(OBJS)
$(CXX) $(CXXFLAGS) -o $# $^ $(LFLAGS) $(LIBS)

Answer 2

I found a solution, that, to my tastes seems elegant, or at least easy to trace using the wildcard operator. Here is my current makefile:
EXEFILE := $(shell basename $(CURDIR))
DIRECTORIES = $(filter-out ./ ./.%, $(shell find ./ -maxdepth 10 -type d))
IFLAGS= -I/usr/include/freetype2
LOCAL_I_DIRS =$(addprefix -I./, $(DIRECTORIES))
LFLAGS= -L/usr/lib/nvidia-375 -L/usr/local/lib -L/usr/include/GL -L/usr/local/include/freetype2 -L/usr/local/lib/
LIBS = -lglfw -lGL -lGLU -lOpenGL -lGLEW -pthread -lfreetype
SRC := $(wildcard *.cpp) $(wildcard **/*.cpp)
$(EXEFILE): $(EXEFILE).cpp
g++ -std=c++11 -o $(EXEFILE) -Wall -Wno-comment $(SRC) $(IFLAGS) $(LOCAL_I_DIRS) $(LFLAGS) $(LIBS)
all: run clean
run: $(EXEFILE)
./$(EXEFILE)
clean:
rm $(EXEFILE)
print-%: ; #echo $* = $($*)
So I get all directories up to depth 10. I then take out the current root (./) and any hidden directory (./.) leaving me with standard subdirectories stored under "DIRECTORIES", I then add -I to every directory to make it an include directory and store them in LOCAL_I_DIRS
So I can now create as many subdirectories as needed (up to 10 levels) and the compiler will be happy.