为C ++程序创建健壮的Makefile

Question

Consider the following trivial Makefile. Notice that there are two classes with corresponding .h and .cpp files for each.

output: main.o class1.o class2.o
    g++ main.o class1.o class2.o -o output

main.o: main.cpp
    g++ -c main.cpp

class1.o: class1.cpp class1.h
    g++ -c class1.cpp

class2.o: class2.cpp class2.h
    g++ -c class2.cpp

clean:
    rm *.o output 

Is this Makefile robust? How can I make it more robust? Can someone provide a more robust version of this Makefile? It will be running on a 64 bit Red Hat Linux or CentOS machine.

If it matters, I am using:

-gcc --version 4.8.4 (From the GNU Compiler Collection)

-GDB version: GNU gdb (Ubuntu 7.7.1 -0ubuntu5~14.04.2) 7.7.1

Answer 1

I would write something like

CXX = g++
# mandatory build flags
AM_CXXFLAGS = -Wall -W -std=gnu++11
# optional build flags
CXXFLAGS = -O2 -Werror

# mandatory link flags
AM_LDFLAGS = -Wl,-as-neeeded

output: main.o class1.o class2.o
    ${CXX} ${AM_LDFLAGS} ${LDFLAGS} $(filter %.o,$^) -o $@

%: %.cpp
    ${CXX} ${AM_CXXFLAGS} ${CXXFLAGS} $< -c -o $@

class1.o: class1.cpp class1.h
class2.o: class2.cpp class2.h

• the *FLAGS are following automake notation: AM_* mean mandatory flags, the normal flags contain local settings (eg debugging or optimiziation).

  Usually, AM_CPPFLAGS and CPPFLAGS with preprocessor flags ( -I ... ) should be used too but I omitted them here

• the output target might need ${LIBS} too which have been omitted here

• dependency tracking is more tricky and not implemented; you will have to play with -dM compiler option here...

When your program consists only of the listed 5 files, you can write

output_SOURCES = main.c class1.c class2.c class1.h class2.h

output: ${output_SOURCES}
        ${CXX} ${AM_CXXFLAGS} ${CXXFLAGS} ${AM_LDFLAGS} ${LDFLAGS} $(filter %.cpp,$^) -o $@ ${LIBS}

directly.

EDIT:

For automatic dependency tracking, you can write

DEPGENFLAGS = \
    -MD -MF ${@D}/.${@F}.d -MT '$@'

%: %.cpp
    ${CXX} ${DEPGENFLAGS} ${AM_CXXFLAGS} ${CXXFLAGS} $< -c -o $@

-include .deps.main.o.d
-include .deps.class1.o.d
-include .deps.class2.o.d

Answer 2

I don't think your original makefile is far off the mark. I've just made a few additions:

1. Added a default all target - it's good to be explicit
2. Use the CXXFLAGS environment variable in all the calls to g++
3. Make main.o depend upon class1.h and class2.h as discussed
4. Specify that clean is a PHONY target just to be on the safe side if you add build artifact called clean

---

ALL := output

all : $(ALL) 

output: main.o class1.o class2.o
    g++ $(CXXFLAGS) main.o class1.o class2.o -o output

main.o: main.cpp class1.h class2.h
    g++ $(CXXFLAGS) -c main.cpp

class1.o: class1.cpp class1.h
    g++ $(CXXFLAGS) -c class1.cpp

class2.o: class2.cpp class2.h
    g++ $(CXXFLAGS) -c class2.cpp

.PHONY : clean

clean:
    rm *.o output 

Answer 3

How can I make it more robust?

Use implicit rules, keep it simple.

LDLIBS+=-lstdc++
output: main.o class1.o class2.o

clean:
    rm *.o output