Support multiple build types with GNU make

makefile

#
# Compiler flags
#
CC = gcc
CFLAGS = -Wall -Werror -Wextra

#
# Project files
#
SOURCES = file1.c file2.c file3.c file4.c
OBJECTS = $(SOURCES:.c=.o)
EXECUTABLE = exefile
BUILD_DIR = build

#
# Debug build settings
#
DEBUG_DIR = $(BUILD_DIR)/debug
DEBUG_EXECUTABLE = $(DEBUG_DIR)/$(EXECUTABLE)
DEBUG_OBJECTS = $(addprefix $(DEBUG_DIR)/, $(OBJECTS))
DEBUG_FLAGS = -g -O0 -DDEBUG

#
# Release build settings
#
RELEASE_DIR = $(BUILD_DIR)/release
RELEASE_EXECUTABLE = $(RELEASE_DIR)/$(EXECUTABLE)
RELEASE_OBJECTS = $(addprefix $(RELEASE_DIR)/, $(OBJECTS))
RELEASE_FLAGS = -O3 -DNDEBUG

.PHONY: all clean debug prep release remake

# Default build
all: release

#
# Debug rules
#
debug: prep $(DEBUG_EXECUTABLE)

$(DEBUG_EXECUTABLE): $(DEBUG_OBJECTS)
	$(CC) $(CFLAGS) $(DEBUG_FLAGS) -o $(DEBUG_EXECUTABLE) $^

$(DEBUG_DIR)/%.o: %.c
	$(CC) -c $(CFLAGS) $(DEBUG_FLAGS) -o $@ $<

#
# Release rules
#
release: prep $(RELEASE_EXECUTABLE)

$(RELEASE_EXECUTABLE): $(RELEASE_OBJECTS)
	$(CC) $(CFLAGS) $(RELEASE_FLAGS) -o $(RELEASE_EXECUTABLE) $^

$(RELEASE_DIR)/%.o: %.c
	$(CC) -c $(CFLAGS) $(RELEASE_FLAGS) -o $@ $<

#
# Other rules
#
prep:
	@mkdir -p $(DEBUG_DIR) $(RELEASE_DIR)

remake: clean all

clean:
	rm -f $(RELEASE_EXECUTABLE) $(RELEASE_OBJECTS) $(DEBUG_EXECUTABLE) $(DEBUG_OBJECTS)