Process all files in variable separatly in Makefile - c++

Question

I have multiple source files in a directory, which some are responsible for a main executable, and some are responsible for a shared library, which then in turn is needed for the main executable. Thus I wrote the makefile in the following way:
CC=gcc
CXX=g++
CFLAGS=-I$(DIR) -fPIC -c -fopenmp
CXXLFLAGS=-I$(DIR) -fopenmp -O3 -g -march=native -std=gnu++17 -fPIC -c
CXXFLAGS=-I$(DIR) -fopenmp -O3 -g -march=native -std=gnu++17 -c
LDFLAGS=-lfftw3 -lgomp -lm -larmadillo -lpthread -lX11 -lboost_system -lboost_program_options -L/opt/intel/mkl/lib/intel64 -lmkl_rt
LDMAINFLAGS=-lfftw3 -lgomp -lm -larmadillo -lpthread -lX11 -lboost_system -lboost_program_options -L/opt/intel/mkl/lib/intel64 -lmkl_rt -lpulse_propagation
LIBSOURCES=source/image_processing.cpp source/pulse_propagation.cpp
LIBOBJECTS=source/image_processing.o source/pulse_propagation.o
MAINSOURCES=source/fftw.cpp source/fftw++.cc
MAINOBJECTS=source/fftw.o source/fftw++.o
EXECUTABLE=fftw
LIBRARY=libpulse_propagation.so
.PHONY: default all clean
default: all
all: $(LIBRARY) main
main: $(LIBRARY) $(MAINOBJECTS)
$(CXX) $(LDFLAGS) $(MAINOBJECTS) -o $(EXECUTABLE)
$(LIBRARY): $(LIBOBJECTS)
$(CXX) $(LDFLAGS) -shared $^ -o $#
$(LIBOBJECTS): $(LIBSOURCES)
$(CXX) $(CXXLFLAGS) $^ -o $#
$(MAINOBJECTS): $(MAINSOURCES)
$(CXX) $(CXXFLAGS) $^ -o $#
clean_compile:
rm -f source/*.o
clean:
rm -f source/*.o $(EXECUTABLE) $(LIBRARY)
with everything labeled with a MAIN belonging to the main executable and everything else to the library. I would like to loop over the files in LIBSOURCES/MAINSOURCES and compile each of them. I would prefer if I do not have to use the .cpp.o:-macro, after there are different flags depending if it is a library file or a main file. I tried using $<, which executed the compilation twice (ok), but always used the first value from the variable list. When using $^ instead, both files are used at once, also resulting in an error. How could I else do that?

Answer 1

Your source/fftw++.cc instead of source/fftw++.cpp makes everything uselessly complex. If you can rename it, then the following should do what you want:
$(LIBOBJECTS): CXXFLAGS := $(CXXLFLAGS)
$(LIBOBJECTS) $(MAINOBJECTS): %.o: %.cpp
$(CXX) $(CXXFLAGS) $< -o $#
The first line defines the value of variable CXXFLAGS for the $(LIBOBJECTS) targets. The following rule is a static pattern rule that translates into as many rules with one target and one prerequisite only. It is completely different from your rules that declares all source files of one kind as prerequisites of all corresponding object files. Not what you want normally.
If you cannot rename source/fftw++.cc you can split your sources and objects lists:
MAINCPPSOURCES=source/fftw.cpp
MAINCCSOURCES=source/fftw++.cc
MAINCPPOBJECTS=source/fftw.o
MAINCCOBJECTS=source/fftw++.o
$(LIBOBJECTS): CXXFLAGS := $(CXXLFLAGS)
$(LIBOBJECTS) $(MAINCPPOBJECTS): %.o: %.cpp
$(CXX) $(CXXFLAGS) $< -o $#
$(MAINCCOBJECTS): %.o: %.cc
$(CXX) $(CXXFLAGS) $< -o $#
Finally, it would probably be better (easier to maintain) if you were computing what can be, instead of hard-wiring it in your Makefile:
MAINCPPOBJECTS = $(patsubst %.cpp,%.o,$(MAINCPPSOURCES))
MAINCCOBJECTS = $(patsubst %.cc,%.o,$(MAINCCSOURCES))
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