How to prevent my makefile to relink due to static library - c++

Question

I have a Makefile which works well when there is not static library to compile:
CC = g++ -std=c++11
RM = rm -f
NAME = hello
SRCS = Main.cpp \
srcs/Controller.cpp \
...
srcs/Parser.cpp
OBJS = $(SRCS:.cpp=.o)
CPPFLAGS += -W -Wall -Wextra -Werror
all : $(NAME)
$(NAME) : $(OBJS)
$(CC) $(CPPFLAGS) $(CFLAGS) -o $(NAME) $(OBJS) -I./inc
clean :
$(RM) $(OBJS)
fclean : clean
$(RM) $(NAME)
re : fclean all
.PHONY : all clean fclean re
This makefile works and doesn't relink (when I type twice "make", it doesn't recompile and output "Nothing to be done for all")
But when I want to compile a static library, the "make" command recompile the library without outputing "Nothing to be done for all", here is the new Makefile containing the static lib:
CC = g++ -std=c++11
RM = rm -f
NAME = hello
LIBNAME = libhello.a
SRCS = srcs/Controller.cpp \
...
srcs/Parser.cpp
OBJS = $(SRCS:.cpp=.o)
CPPFLAGS += -W -Wall -Wextra -Werror
all : $(NAME)
$(NAME) : $(OBJS)
ar rc $(LIBNAME) $(OBJS)
$(CC) $(CPPFLAGS) $(CFLAGS) -o $(NAME) $(LIBNAME) Main.cpp -I./inc
clean :
$(RM) $(OBJS)
$(RM) $(LIBNAME)
fclean : clean
$(RM) $(NAME)
re : fclean all
.PHONY : all clean fclean re
How could I fix that problem to prevent the makefile to recompile when the static library has already been compiled and doesn't need to be recompiled ?
Thank you very much

Answer 1

regarding this recipe:
$(NAME) : $(OBJS)
$(CC) $(CPPFLAGS) $(CFLAGS) -o $(NAME) $(OBJS) -I./inc
it is expecting that the default compile statement will be used to generate the object files and make will generate those object files before executing the rule. and since it is not performing any compiles in this recipe, the parameter -I./inc is unneeded.
Without the header files being listed in the dependencies, changing a header file will fail to cause the associated source files to be recompiled.
Suggest:
HEADERS := ..
$(name): $(OBJS)
<tab> $(CC) -o $# $(OBJS) $(LFLAGS)
%.o:%.cpp $(HEADERS)
<tab> $(CC) $(CPPFLAGS) -c $< -o $# -I./inc
Note in the line:
CPPFLAGS += -W -Wall -Wextra -Werror
the -W turns off all the previously enabled warnings, probably not what you want, suggest removing that parameter.
Similar considerations need to be applied when creating the static library, similar to:
this line:
$(NAME) : $(OBJS)
ar rc $(LIBNAME) $(OBJS)
$(CC) $(CPPFLAGS) $(CFLAGS) -o $(NAME) $(LIBNAME) Main.cpp -I./inc
becomes:
HEADER := ...
all: $(LIBNAME) $(NAME)
$(LIBNAME): $(OBJS)
<tab> ar rc -o $# $^
%.o:%.cpp
<tab> $(CC) $(CPPFLAGS) -c $< -o $# -I./inc
$(NAME): main.o $(LIBNAME)
<tab> $(CC) $< -o $# $(LFLAGS) -l$(LIBNAME)

Answer 2

The issue is that $NAME is a phony target due to this rule:
all : $(NAME)
I think the issue can be resolved by instead changing it to an actual target:
all : $(LIBNAME)
Also, you have this rule:
$(NAME) : $(OBJS)
ar rc $(LIBNAME) $(OBJS)
$(CC) $(CPPFLAGS) $(CFLAGS) -o $(NAME) $(LIBNAME) Main.cpp -I./inc
It is a bit confusing: The library is built as $LIBNAME, but then it goes on to link an executable named $NAME. So everytime you make a change to Main.cpp, the library has to be rebuilt.

Answer 3

Your rule for $(NAME) doesn't actually make a file called $(NAME) (i.e. hello), so make will try and remake it every time. The recipe must match the rule (and this is why you should use automatic variables as in the last example below):
all: $(LIBNAME)
$(LIBNAME): $(OBJS)
ar rc $(LIBNAME) $(OBJS)
GNU make also has built-in archive functionality, although it doesn't play well with parallel make:
ARFLAGS := rc
all: $(LIBNAME)($(OBJS))
A more idiomatic, parallel-safe way would be something like
ARFLAGS := rc
.PHONY: all
all: $(LIBNAME)
$(LIBNAME): $(OBJS)
$(AR) $(ARFLAGS) $# $^