add format to make

Makefile

@@ -32,4 +32,9 @@ re:
 		$(MAKE) -C $$ex re; \
 	done
 
-.PHONY: all clean fclean re
+format:
+	for ex in $(EX); do \
+		$(MAKE) -C $$ex format; \
+	done
+
+.PHONY: all clean fclean re format

common.mk

@@ -16,6 +16,8 @@ SRC = $(notdir $(wildcard src/*.cpp))
 OBJ    = $(SRC:.cpp=.o)
 CC     = c++
 CFLAGS = -Wall -Wextra -Werror -std=c++11
+FORMATTER = clang-format
+FORMAT_FILES = $(wildcard src/*.[ch] src/*.[ch]pp inc/*.[ch] inc/*.[ch]pp)
 
 all: $(NAME)
 
@@ -36,4 +38,17 @@ fclean: clean
 
 re: fclean all
 
-.PHONY: all clean fclean re run
+format:
+	@if command -v $(FORMATTER) >/dev/null 2>&1; then \
+		if [ -n "$(FORMAT_FILES)" ]; then \
+			$(FORMATTER) -i --style=file $(FORMAT_FILES); \
+			printf "Formatted %s\n" "$(NAME)"; \
+		else \
+			printf "No files to format in %s\n" "$(NAME)"; \
+		fi; \
+	else \
+		printf "clang-format not found. Please install clang-format.\n"; \
+		exit 1; \
+	fi
+
+.PHONY: all clean fclean re run format