Makefile tutorial: http://www.cs.colby.edu/maxwell/courses/tutorials/maketutor/

normally type in terminal
gcc -o hellomake hellomake.c hellofunc.c -I.
(-I. : gcc will look in the current directory (.) for the include files)
2 problems: inefficient / not automatized + have to recompile everything everytime

Makefile: "makefile" or "hello.make" etc
command: make : executes the first rule in the file


Some macros:
$@: name before the : in rule head
$^: after the : in rule head
S<: first item after : in rule head
$(NAME): access a macro
name headers DEPS
name object files OBJ
name compiler CC
name flags CFLAGS

EX1:
hellomake: hellomake.c hellofunc.c
     gcc -o hellomake hellomake.c hellofunc.c -I. 

Note 1: By putting the list of files on which the command depends on the first line after the :, make knows that the rule hellomake needs to be executed if any of those files change. 

Note 2: need tab before the gcc command


EX2:
CC=gcc
CFLAGS=-I.

hellomake: hellomake.o hellofunc.o
     $(CC) -o hellomake hellomake.o hellofunc.o -I.

Note 1: variables / macros used : VARNAME=string then use $(VARNAME)

Note 2: putting the object files: knows that the .c files must be compiled individually


EX3:
CC=gcc
CFLAGS=-I.
DEPS = hellomake.h

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

hellomake: hellomake.o hellofunc.o 
  gcc -o hellomake hellomake.o hellofunc.o -I.

Note 1: new macro for header file

Note 2: new rule: any object file depends on corresponding .c file + headers

Note 3:
  -the -c flag says to generate the object file 
  -the -o $@ says to put the output of the compilation in the file named on the left side of the : 
  -the $< is the first item in the dependencies list


EX4:
CC=gcc
CFLAGS=-I.
DEPS = hellomake.h
OBJ = hellomake.o hellofunc.o 

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

hellomake: $(OBJ)
  gcc -o $@ $^ $(CFLAGS)

Note 1: Better syntax



EX5:
IDIR =../include
CC=gcc
CFLAGS=-I$(IDIR)

ODIR=obj
LDIR =../lib

LIBS=-lm

_DEPS = hellomake.h
DEPS = $(patsubst %,$(IDIR)/%,$(_DEPS))

_OBJ = hellomake.o hellofunc.o 
OBJ = $(patsubst %,$(ODIR)/%,$(_OBJ))


$(ODIR)/%.o: %.c $(DEPS)
  $(CC) -c -o $@ $< $(CFLAGS)

hellomake: $(OBJ)
  gcc -o $@ $^ $(CFLAGS) $(LIBS)

.PHONY: clean

clean:
  rm -f $(ODIR)/*.o *~ core $(INCDIR)/*~ 

Note 1: libraries, includes and objects now in other directories

Note 2: macro for libraries we want to include: -lm is the math lib

Note 3: make clean cleans up directories / .PHONY makes the file named "clean" ignored

Note 4: http://web.mit.edu/gnu/doc/html/make_4.html