Makefile.md

Makefile

Solve the problem of having to worry about compilation each time you make a change to each module.

<target>: [ <dependency > ]*
   [ <TAB> <command> <endl> ]+

The above will run the commands listed for any targets that have dependencies that have been updated.

.PHONY: <target>`

.PHONY are used to tell Make that the target is not associated with files.

An example is clean

.PHONY: clean
clean:
  rm -rf *.o

You can now run make clean even if you have a file named clean.

We can use variables instead of listing all of our commands separately.

CXX = g++
CXXFLAGS = -Wall (warn all)
OBJECTS = main.o book.o ...
EXEC = main

${EXEC}: ${OBJECTS}
    ${CXX} ${CXXFLAGS} ${OBJECTS} -o ${EXEC}

main.o: <dependencies>

book.o <dependencies>

...

.PHONY: clean

clean: 
    rm ${OBJECTS} ${EXEC}

Doing this will go through the OBJECTS and abstracts away the commands that were entered manually before.

We can take this one step further:

CXX = g++
CXXFLAGS = -Wall -MMD -g
EXEC = main
OBJECTS = main.o book.o textbook.o comic.o ...
DEPENDS = ${OBJECTS:.o=.d}

${EXEC}: ${OBJECTS}
    ${CXX} ${CXXFLAGS} ${OBJECTS} -o ${EXEC}

-include ${DEPENDS}

.PHONY: clean

clean:
    rm ${OBJECTS} ${EXEC} ${DEPENDS}

• Now all we have to do is change the list of OBJECTS whenever we add more files to the project
• -include will look for the files in DEPENDS and include them in the Makefile (these are other Makefiles)
  • Notice the addition of -MMD, which will auto-create the list of dependencies that we had to manually enter before
    • e.g.) main.o:
  • These will be created as .d files and then Make will include them much like a copy and paste
• The line ${OBJECTS:.o=.d} takes the value of ${OBJECTS} and replaces .o with .d
• The - infront of -include is needed since .d files may not exist for newly created files in the project. The hyphen tells Make to skip the warning and move on.
• If the .d file doesn't exist, then neither will the .o so the command will be executed and both will be created.

PROTIP:

If getting an error: Makefile:_: *** missing separator. Stop

Use Ctrl-V, Ctrl-I in VIM while in insert mode to insert a real tab character.

(Just in case your VIM isn't configured to use tabs)