如何用Gnu make编写库？

Question

I'm trying to create a library, called Aa, that provides a class A, which depends on the classes B and C, all in their respective files ( .cpp and .hpp ). I usually compiled all my code manually, but as the number of files increased, I wanted to use a makefile. Basically, what I would do was:

g++ -c A.cpp
g++ -c B.cpp
g++ -c C.cpp
ar rvs A.a *.o

How can I construct a makefile that does this? Can makefiles even call ar ?

This is what I tried:

CC=g++
CFLAGS=-c -Wall
objects=C.o B.o

all : A.o $(objects) #Creates the library called A.a.
:ar rvs A.a A.o $(objects)

A.o : $(objects) A.hpp A.cpp
:$(CC) $(CFLAGS) A.cpp

B.o : B.hpp B.cpp
:$(CC) $(CFLAGS) B.cpp

C.o : C.hpp C.cpp
:$(CC) $(CFLAGS) C.cpp

But it seems that my ar rvs Aa Ao $(objects) instruction isn't even executing. This makefile produces all the correct .o files, but doesn't archive them.

Answer 1

You could use rules and patterns to make it more generic:

SRC_DIR = .
CPPFLAGS += -g
INCLUDES = -I.

# variant 1
SRCS ?= $(shell find $(SRC_DIR) -name '*.cpp' | sed "s/[^\/]*\/[^\/]*\///")
# variant 2
SRCS = A.cpp B.cpp

%.o : $(SRC_DIR)/%.cpp
    $(CXX) -o $@ $(INCLUDES) $(CPPFLAGS) -c $^

all : A.a

A.a : $(SRCS:.cpp=.o) 
    $(AR) rsv $@ $^

Answer 2

OK, so my syntax was correct after all, or, at least, a big portion of it was. I went with a wrong premise that : 's could replace tabs, which is, apparently, not correct after all.

So, this is the code that does what I want:

CC=g++
CFLAGS=-c -Wall
objects=B.o C.o

all : A.a

A.o : $(objects) A.hpp A.cpp
    $(CC) $(CFLAGS) A.cpp

B.o : B.hpp B.cpp
    $(CC) $(CFLAGS) B.cpp

C.o : C.hpp C.cpp
    $(CC) $(CFLAGS) C.cpp

A.a : A.o $(objects)
    ar rvs A.a A.o $(objects)