创建一个makefile并在子目录中进行编译

Question

There is this nice makefile (from this tutorial: https://sites.google.com/site/michaelsafyan/software-engineering/how-to-write-a-makefile ). However, also as mentioned on the web site, this makefile compiles all the .c and .cpp files from single directory to an executable.

program_NAME := myprogram
program_C_SRCS := $(wildcard *.c)
program_CXX_SRCS := $(wildcard *.cpp)
program_C_OBJS := ${program_C_SRCS:.c=.o}
program_CXX_OBJS := ${program_CXX_SRCS:.cpp=.o}
program_OBJS := $(program_C_OBJS) $(program_CXX_OBJS)
program_INCLUDE_DIRS :=
program_LIBRARY_DIRS :=
program_LIBRARIES :=

CPPFLAGS += $(foreach includedir,$(program_INCLUDE_DIRS),-I$(includedir))
LDFLAGS += $(foreach librarydir,$(program_LIBRARY_DIRS),-L$(librarydir))
LDFLAGS += $(foreach library,$(program_LIBRARIES),-l$(library))

.PHONY: all clean distclean

all: $(program_NAME)

$(program_NAME): $(program_OBJS)
    $(LINK.cc) $(program_OBJS) -o $(program_NAME)

clean:
    @- $(RM) $(program_NAME)
    @- $(RM) $(program_OBJS)

distclean: clean

How is it possible to modify this makefile such that it compiles following program? eg, if my directories have following structure:

/project
    Makefile
    main.cpp
    /src
        Class1.cpp
        Class2.cpp
    /obj
        Class1.obj
        Class2.obj
    /bin
        myProgram
    /inc
        Class1.h
        Class2.h
    /lib
        libX.a

Answer 1

Dan. As others have mentioned in the comments, you really ought to use CMake or some other build system that generates makefiles (and other projects) rather than creating a makefile by hand.

With the makefile that I provided in the tutorial, it's important to understand what each of the various variables represent. The program_C_SRCS and program_CXX_SRCS represent the C and C++ source files that are to be built. You can modify the wildcard such that they are picked up from the "src" directory rather than from the current directory. Likewise, the OBJS variables define the list of object files that are produced as output. You can similarly modify the way that this is constructed so that they get emitted in the "obj" subdirectory (though without further testing, I'm unsure whether the normal inference that xo is generated from x.cpp will survive if they span different directories... you'll have to see for yourself).

As for including the headers from a different directory, the program_INCLUDE_DIRS is defined for this very purpose. Just use program_INCLUDE_DIRS := inc , and the "inc" folder should be added to the list of directory for which to search for includes. Likewise, you can link against the library libX.a library by adding the "lib" directory to program_LIBRARY_DIRS and adding "X" to program_LIBRARIES .

In any event, knowing how makefiles work is useful both for historical purposes and for debugging / understanding how the tools that generate makefiles work. However, it is really inadvisable in this day and age to write your own makefiles. Please, please, please invest some time into learning CMake . While there is some upfront time investment in learning a new tool such as CMake, it will save you a lot of time in the long run over writing extremely contorted Makefiles that are fragile and slow to build.