Makefile basics

Question

I am having trouble with the basics of makefile.

I use gcc to compile

What I need to do is make a makefile named labMakefile and the targets are

lab
labM.o
labG.o
clean

the files already in the folder that i'm working on consist of

labM.c
labM.o
labG.c
labG.o

I have been looking at makefile tutorials but I cant seem to find the proper way to create a makefile

What i have tried

labMakefile: labM.o labG.o

but it just says labMakefile:: command not found

Answer 1

A makefile is a script which is run by Make. It is just a text file written with a strict grammar which Make needs, like source code (although it is interpreted, not compiled). You can use any text editor you like to create it.

You are using C (judging by the suffixes on your filenames). So to create labM.o from labM.c you'd probably use a command like

gcc -c labM.c -o labM.o

(Not that the -o labM.o is really needed, it's the default behavior, I'm just trying to spell things out a little.) Likewise to build labG.o you'd use

gcc -c labG.c -o labG.o

and then (I guess) you'd link them together to build lab:

gcc labM.o labG.o -o lab

And sometimes you'd want to clear out the constructed files:

rm -f *.o lab

So to do all of this, you'd write a makefile called Makefilethat looked like this (note that the leading spaces are TABs):

labM.o:
    gcc -c labM.c -o labM.o

labG.o:
    gcc -c labG.c -o labG.o

lab:
    gcc labM.o labG.o -o lab

.PHONY:clean
clean:
    rm -f *.o lab

Then you could make lab or make clean or make labM.o labG.o. If you really want to call this makefile labMakefile, you can do so, but then you'll have to do e.g. make -f labMakefile lab. This makefile is crude but effective. It could be greatly improved upon:

CC = gcc

lab: labM.o labG.o
    gcc $^ -o $@

lab%.o: lab%.c
    $(CC) -c $< -o $@

.PHONY:clean
clean:
    @echo cleaning things up, boss...
    @rm -f *.o lab

This will handle dependencies better: if you modify labM.c but not labG.c, and then make, Make will know that labM.o (and lab) must be rebuilt, but labG.o need not be.

This is a lot to take in, and further improvement is possible (dependency handling can be made very slick), but it's a good start.

Answer 2

To run a makefile, you must invoke "make"

If your makefile has not a standard name (makefile or Makefile), you should specify it with the -f argument :

make -f labMakefile