Compiling your source code files can be tedious, specially when you want to include several source files and have to type the compiling command everytime you want to do it.
Well, I have news for you... Your days of command line compiling are (mostly) over, because YOU will learn how to write Makefiles.
Makefiles are special format files that together with the make utility will help you to automagically build and manage your projects.
For this session you will need these files:
note: I use g++ for compiling. You are free to change it to a compiler of your choice
The make utilityIf you run
makethis program will look for a file named makefile in your directory, and then execute it.
If you have several makefiles, then you can execute them with the command:
make -f MyMakefileThere are several other switches to the
Compiling by handThe trivial way to compile the files and obtain an executable, is by running the command:
g++ main.cpp hello.cpp factorial.cpp -o hello
The basic MakefileThe basic makefile is composed of:
target: dependencies [tab] system commandThis syntax applied to our example would look like:
all: g++ main.cpp hello.cpp factorial.cpp -o hello[Download here]
To run this makefile on your files, type:
make -f Makefile-1On this first example we see that our target is called all. This is the default target for makefiles. The make utility will execute this target if no other one is specified.
We also see that there are no dependencies for target all, so make safely executes the system commands specified.
Finally, make compiles the program according to the command line we gave it.
Using dependenciesSometimes is useful to use different targets. This is because if you modify a single file in your project, you don't have to recompile everything, only what you modified.
Here is an example:
all: hello hello: main.o factorial.o hello.o g++ main.o factorial.o hello.o -o hello main.o: main.cpp g++ -c main.cpp factorial.o: factorial.cpp g++ -c factorial.cpp hello.o: hello.cpp g++ -c hello.cpp clean: rm -rf *o hello[Download here]
Now we see that the target all has only dependencies, but no system commands. In order for make to execute correctly, it has to meet all the dependencies of the called target (in this case all).
Using variables and commentsYou can also use variables when writing Makefiles. It comes in handy in situations where you want to change the compiler, or the compiler options.
# I am a comment, and I want to say that the variable CC will be # the compiler to use. CC=g++ # Hey!, I am comment number 2. I want to say that CFLAGS will be the # options I'll pass to the compiler. CFLAGS=-c -Wall all: hello hello: main.o factorial.o hello.o $(CC) main.o factorial.o hello.o -o hello main.o: main.cpp $(CC) $(CFLAGS) main.cpp factorial.o: factorial.cpp $(CC) $(CFLAGS) factorial.cpp hello.o: hello.cpp $(CC) $(CFLAGS) hello.cpp clean: rm -rf *o hello[Download here]
As you can see, variables can be very useful sometimes. To use them, just assign a value to a variable before you start to write your targets. After that, you can just use them with the dereference operator $(VAR).
Where to go from hereWith this brief introduction to Makefiles, you can create some very sophisticated mechanism for compiling your projects. However, this is just a tip of the iceberg. I don't expect anyone to fully understand the example presented below without having consulted some Make documentation (which I had to do myself) or read pages 347 to 354 of your Unix book.
CC=g++ CFLAGS=-c -Wall LDFLAGS= SOURCES=main.cpp hello.cpp factorial.cpp OBJECTS=$(SOURCES:.cpp=.o) EXECUTABLE=hello all: $(SOURCES) $(EXECUTABLE) $(EXECUTABLE): $(OBJECTS) $(CC) $(LDFLAGS) $(OBJECTS) -o $@ .cpp.o: $(CC) $(CFLAGS) $< -o $@[Download here]
If you understand this last example, you could adapt it to your own personal projects changing only 2 lines, no matter how many additional files you have !!!.