Automate Your Builds with Make: Understanding Makefiles and Compilation Processes

1. Make • Make is a system utility that automatically compiles your programs for you • Make looks for a file named Makefile (or makefile) in the current directory • Describes the relationships among files that comprise you program • Gives the commands for updating each file • Using the Makefile, make automatically: • Determines which files need to be recompiled • Issues the commands to recompile them

2. A Simple Program // hello.cpp #include <iostream> #include “hello.h” using namespace std; int main() { cout << MESSAGE << endl; }

3. The Header File // hello.h #define MESSAGE "Hello World!"

4. Compiling and Running the Program • Compiling: • g++ -O2 -o hello hello.cpp • Running • ./hello • Result: • Hello World!

5. Makefile • Composed of: • Comments (from a pound sign to the end of a line) # This is a comment • Macros – just like in your program CFLAGS= -O2 • Targets – lists dependencies and rules for updating hello: hello

6. The Makefile # Makefile for hello.cpp CFLAGS = -O2 hello: hello.h hello.cpp g++ $(CFLAGS) -o hello hello.cpp

7. Compiling and Running the Program with Make • Compiling: • make • Running • ./hello • Result: • Hello World! • Note: make is really unnecessary for such a simple program, but is essential for programs with lots of source files

8. Make - Pitfalls • Make is very picky about some things: • Indenting must be done with tabs not spaces • Dependencies must be correct • If nothing has changed make will tell you the target is “up to date”

9. A More Complicated Example • 5 source files • Some shared header files • Multiple targets • Make creates the first target by default • E.g. make • You can specify others: • E,g, make clean

10. Let’s Write a Makefile • 3 header files • src1.h – used by src1.cpp • src2.h – used by src2.cpp • global.h – used by src1.cpp, src2.cpp, and main.cpp • 4 source files • src1.cpp – routines used by main.cpp • src2.cpp – routines used by main.cpp • src3.cpp – routines used by src2.cpp • main.cpp – main program

11. Questions • What will make do if we touch: • global.h? • src1.h? • src2.h? • src3.cpp? • main.cpp?