How to use C++ modules with a Makefile? - c++

Question

I have a Makefile which is minimal, yet complete. It is the following:
OUT = example
INSTALL_DIR = /usr/local/bin
OBJECT = ./obj
SOURCE = ./src
SRC := $(shell find $(SOURCE) -name *.cc)
OBJ := $(SRC:%=$(OBJECT)/%.o)
DEPS := $(OBJ:.o=.d)
INC_DIRS := $(shell find $(SOURCE) -type d)
INC_FLAGS := $(addprefix -I,$(INC_DIRS))
CC = gcc
CFLAGS = -pipe -fmodules-ts -std=c++2a
DEBUG_FLAGS := $(CFLAGS) -g -Wall -Wextra
RELEASE_FLAGS := $(CFLAGS) -O3 -flto
debug: $(OBJ)
#echo "Building the DEBUG binary..."
#$(CC) $(OBJ) -o $(OUT) $(DEBUG_FLAGS)
#echo "The binary was built successfully!"
release: $(OBJ)
#echo "Building the RELEASE binary..."
#$(CC) $(OBJ) -o $(OUT) $(RELEASE_FLAGS)
#echo "The binary was built successfully!"
install: $(OUT)
#cp $(OUT) $(INSTALL_DIR)
uninstall:
#rm $(INSTALL_DIR)/$(OUT)
$(OBJECT)/%.cc.o: %.cc
#mkdir -p $(dir $#)
#echo "Building $#..."
#$(CC) $(CFLAGS) -c $< -o $#
.PHONY: clean
clean:
rm -rf $(OBJECT) $(OUT)
-include $(DEPS)
There is a directory called "src" which includes the source files. When I'm running make, I will get a compilation error about having to first create modules before using them. If I do create them manually, then I will be able to use "Make" and it will work then it will work. Is there a way to automatically create them?

Answer 1

I recommend using g++-11 instead of just gcc, since versions <=10 do not really include module support asides from the deprecated TS. Then also, use flag -std=c++20.
Also, I have (painful) experience using dependency files with gcc, since that particular feature is not really fully implemented. Last I checked (beginning of nov '21) the dependency files don't actually do anything as pertains to modules.
That being said, what you write should work. And it would, if the compiler-support for modules was finished.