Thread: Can someone give me a very quick and simple explanation of how to make a makefile

A makefile is a database of rules read by the make program that describes how to make your program. Here's an example for 3 .c files where two of them have associated .h files:

Code:

prog : prog.o util.o stuff.o
	gcc -o prog prog.o util.o stuff.o

prog.o : prog.c util.h stuff.h
	gcc -c prog.c

util.o : util.c util.h
	gcc -c util.c

stuff.o : stuff.c stuff.h
	gcc -c stuff.c

The rule format is

Code:

target : prerequisites
	recipe

It's IMPORTANT to use a TAB before the recipe lines (that's what marks them as recipe lines, and there can be more than one).

If you put the above into a file called Makefile (or makefile), then just typing make while in that directory will run make with that makefile. make (when run by just typing make) checks to see if the first target is out of date by comparing its last modification time to that of its prerequisites. If any of the prerequisites are newer than the target, or the target does not exist, then the recipe is executed. The recipe is (usually) designed to re-create the target. If any of the prerequisites is out of date relative to their prerequisites then their recipes will be executed before the main target's recipe.

It doesn't really matter which file has main defined in it, but the above scenario presumably has main defined in prog.c.

There are other things, like variables and fake files (clean, for example), implicit rules, etc., but the above is enough to get you started. Read GNU `make' to learn all about it.