Makefile

Seen in CS247 - Software Engineering Principles. CS247 Lecture 8 and CS247 Lecture 7

Once you master how Makefile works, move on to CMake.

Resources:

• https://makefiletutorial.com/ (REALLY GOOD)

Example:

CXX=g++
CXXFLAGS= -std=c++14 -Wall -g -MMD
EXEC = myprogram
OBJECTS=${CCFILES:.cc=.o}
DEPEND=${CCFILES: .cc=.d}
${EXEC}: ${OBJECTS} 
	${CXX} ${OBJECTS} -o ${EXEC}
-include ${DEPENDS}

Example:

• main.cc (includes List.h)
• List.h
• List.cc (includes List.h)

:= vs. = Syntax

Turns out that you can also use := to define the variables. The difference is that if you assign it to another variable using :=, you need to make sure that the variable is defined before.

The ESENCE OF MAKE: target: preqrequisite

• this is how make is able to detect changes (they use timestamps of files as a heuristic)

Makefile (v1)

myprogram: main.o, List.o
myprogram (TAB) g++ main.o List.o -o myprogram

• General format for first line is target: dependencies
• g++ main.o List.o -o myprogram is called the recipe

main.o : main.cc List.h
	g++ -std=c++14 main.cc -c

List.o : List.cc List.h
	g++ -std=c++14 main.cc -c

This text is in a Makefile in our directory.

make → creates the first target

Looks at the last modified time of dependencies.

If last modified time is newer for a dependency than a target ⇒ target is out of date, recreate it.

Still too much work! Still requires lots of updates to our makefile.

Makefile(V2)

CXX = g++
CXXFLAGS = -std=c++14 -Wall -g -MMD
EXEC = myprogram
CCFILES = $(wildcard *.cc)
OBJECTS = ${CCFILES:.cc=.o}
DEPENDS = ${CCFILES:.cc=.d}
${EXEC}: ${OBJECTS}
	${CXX} ${CXXFLAGS} ${OBJECTS} -o ${EXEC}
-include ${DEPENDS}

For CXXFLAGS

• -Wall for more warnings
• -g for extra debugging support (so you can use gdb)
• -MMD to generate dependency information as a side-effect of compilation. The compiler will create a .d file for each .cpp file you compile. These .d files are makefile fragments that the make program can use to determine which .cpp files need to be recompiled when a header file changes.

- include ${DEPENDS}

• Compiles all object files with dependencies using CXX and CXXFLAGS

CXXFLAGS doesn't seem to be used??

How does it know to use those flags then? StackOverflow has same question.