How do I make Makefile to recompile only changed files?

Question

I have been struggling a bit to get make to compile only the files that have been edited. However I didn\'t have much success and all the files get recompiled. Can someone e

Answer 1

This very late after the fact, and actually it's based on paxdiablo's excellent answer, but while experimenting i found that you don't need separate targets for each .o file unless you're doing something clever.

So for my makefile:

all: program

program: a_functions.o main.o
    gcc a_functions.o main.o -o program

clean: 
    rm -f *.o
    rm -f program

In make 4.1 it compiles the .o files automatically, you don't have to do anything if your .o files have the same names as your source files. So, it will go and hunt for a_functions.c, a_functions.h, main.h and main.c automagically. If you don't have the expected source code names, then you'll get an error like:

make: *** No rule to make target 'a_functions.o', needed by 'program'.  Stop.

I have also added a "clean" target for you. "Clean" is useful if you need to release your software as source code, or you just want to remove all the compiled object files and / or binaries.

And this is all you need to do.

Save this to "Makefile" and run:

$ make

to build your binary. And

$ make clean 

to clean up the compiled objects and binaries in your code.