Makefile in C with multiple sources

Question

I am currently learning C and now I am upto the tutorial where I need to write the Makefile but I am difficulty writing a Makefile for multiple sources. Can someone tell me how I can correct my code for the Makefile for multiple sources? All of the files are in the same directory and there are a total of 3 C source files as indicated by filename1/2/3 etc. I am trying to build 3 separate programs with 3 source files in a single makefile

 OPT = -O4              

all: filename1

filename1: filename1.o 
    gcc $(OPT) -o filename1 filename1.o

filename1.o: filename1.c
    gcc $(OPT) -c filename1.c

filename2: filename2.o 
    gcc $(OPT) -o filename2 filename2.o

filename2.o: filename2.c
    gcc $(OPT) -c filename2.c   

filename3: filename3.o 
    gcc $(OPT) -o filename3 filename3.o

filename3.o: filename3.c
    gcc $(OPT) -c filename3.c       
clean:
    rm -f *.o
    rm -f filename1
    rm -f filename2
    rm -f filename3

Or is my code fine for what I want it to do?

Answer 1

Okay, so there doesn't appear to be anything wrong with the makefile, given that you're making three different programs. It should work.

Some suggestions for making it a little more usable:

1) Declare the "all" and "clean" targets to be phony. This will prevent Make from trying to make files called "all" and "clean".

.PHONY: all clean

2) You probably want your "all" target to build all three of your programs, not just one, so change that to:

all: filename1 filename2 filename3

3) If you end up using this to make more than three programs, and they all share similar build procedures, you can collapse your rules into a smaller set using pattern matches. See Martin Beckett's answer for an example. But, that's not necessary.

Answer 2

Your makefile should work, but it could be simplified.

The make utility supports implicit rules. This can simplify common operations, such as compiling a C source code file into an object file and compiling an object file into an executable.

CC=gcc
CFLAGS=-O4

all: filename1 filename2 filename3

%.o: %.c
    $(CC) $(CFLAGS) -c $<

%: %.o
    $(CC) $(CFLAGS) -o $* $<

clean:
    rm -f *.o
    rm -f filename1
    rm -f filename2
    rm -f filename3