Make

A program for directing recompilation

GNU make
Automatically determines which pieces of a large program need to be recompiled, and issues commands to recompile them
Not limited to C programs

Motivation

Complex projects
- Many lines of code
- Multiple components
- More than one programmer
Division to components is desired
- Long files are harder to manage (humans and machines)
- Every change requires long compilation
- Many programmers can not modify the same file simultaneously

The makefile structure

target ... : prerequisites ...
command

simple example

prog: prog.o
	gcc prog.o -o prog
prog.o: prog.c
	gcc -Wall -c prog.c

The goals are the targets that make should strive ultimately to update
Other targets are updated as well if they appear as prerequisites of goals, or prerequisites of prerequisites of goals, etc.

The make process

Each changed C source file is recompiled
Each C source file that includes a changed header file is recompiled (to be safe)
Each compilation produces an object file corresponding to the source file
If any source file has been recompiled, all the object files (newly made or saved from previous compilations), are linked together to produce the new executable

Running make

Edit a file called the makefile that describes the relationships among files in your program and provides commands for updating each file in make format
Type:
make
By default make tries the following in order:
- GNUmakefile
- makefile - best choice, if source-file names start with upper case
- Makefile - best choice, if source-file names start with lower case
To tell make to read the file name as the makefile, type:
make -f name
By default, the goal is the first target in the makefile
Specify a different goal or goals with arguments to make
- Several goals are made in the order specified
make target1 target2 target3

Another example

btree example - source files: prog.c btree.c btree.h

Project structure and dependencies can be represented as a DAG

prog: prog.o btree.o
	gcc prog.o btree.o -o prog

btree.o: btree.c btree.h
        gcc -c btree.c -o btree.o
        
prog.o: prog.c btree.h
        gcc -c prog.c -o prog.o
       
clean:
	rm -rf btree.o prog.o prog

Variables make makefiles simpler

btree example

CSOURCES = prog.c btree.c
OBJECTS = $(CSOURCES:.c=.o)

prog: $(OBJECTS)
	gcc $? -o $@

btree.o: btree.c btree.h
        gcc -c $< -o $@
        
prog.o: prog.c btree.h
        gcc -c $< -o $@
       
clean:
	rm -rf btree.o prog.o prog

Pattern Rules

Instructs make that the command `bison -d x.y' will make both x.tab.c and x.tab.h
%.tab.c %.tab.h: %.y bison -d $<

Implicit Rules

Predefined rules always available

Compiling C sourse

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

Linking objects
x: y.o z.o
- when `x.c', `y.c' and `z.c' all exist

Adding dependencies

prog: prog.o btree.o
btree.o: btree.h
prog.o: btree.h
       
clean:
	rm -rf btree.o prog.o prog

Shorter makefile (more generic)

Using variables, implicit rules and pattern rules

CSOURCES = btree.c prog.c
OBJECTS = $(CSOURCES:.c=.o)
TARGET = btree
CPPFLAGS =
CFLAGS = -Wall -pedantic

$(TARGET): $(OBJECTS)
btree.o: btree.h
prog.o: btree.h
clean:
        rm -rf $(OBJECTS) $(TARGET)

The output

gcc -Wall -pedantic   -c -o btree.o btree.c
gcc -Wall -pedantic   -c -o prog.o prog.c
gcc   btree.o prog.o   -o btree

Example: photo

linux gcc (gnu) makefile

CSOURCES = photo.c
OBJECTS = $(CSOURCES:.c=.o)
TARGET = $(CSOURCES:.c=)
CPPFLAGS =
CFLAGS = -Wall -pedantic
LDFLAGS = -lglut

$(TARGET): $(OBJECTS)
clean:
        rm -rf $(OBJECTS) $(TARGET)

Example: photo

Windows gcc (gnu cygwin) makefile

CSOURCES = photo.c
OBJECTS = $(CSOURCES:.c=.o)
TARGET = $(CSOURCES:.c=)
CPPFLAGS =
CFLAGS = -Wall -pedantic
LDFLAGS = -lglut32 -lopengl32

$(TARGET): $(OBJECTS)
        gcc $(OBJECTS) $(LDFLAGS) -o $@
clean:
        rm -rf $(OBJECTS) $(TARGET)

Example: photo

Windows cl (MSVC) makefile

CSOURCES = cp_photo.c
OBJECTS = $(CSOURCES:.c=.obj)
TARGET = $(CSOURCES:.c=.exe)
CPPFLAGS =
CFLAGS = -nologo -I.
CPPFLAGS =
LDFLAGS = -nologo -subsystem:console glut32.lib opengl32.lib

$(TARGET): $(OBJECTS)
        link $(OBJECTS) $(LDFLAGS) -Out:$@
%.obj : %.c
        cl $(CFLAGS) -c $<
clean:
        rm -rf $(OBJECTS) $(TARGET)

Example: photo

Combined makefile

ifeq ($(OS), Windows)
CSOURCES = cp_photo.c
OBJECTS = $(CSOURCES:.c=.obj)
TARGET = $(CSOURCES:.c=.exe)
CFLAGS = -nologo -I.
LDFLAGS = -nologo -subsystem:console glut32.lib opengl32.lib
else
CSOURCES = photo.c
OBJECTS = $(CSOURCES:.c=.o)
TARGET = $(CSOURCES:.c=)
CFLAGS = -Wall -pedantic
ifeq ($(OSTYPE), linux)
LDFLAGS = -lglut
else
LDFLAGS = -lglut32 -lopengl32
endif
endif
CPPFLAGS =

$(TARGET): $(OBJECTS)
ifeq ($(OS), Windows)
        link $(OBJECTS) $(LDFLAGS) -Out:$@

%.obj : %.c
        cl $(CFLAGS) -c $<
else
        gcc $(OBJECTS) $(LDFLAGS) -o $@
endif

clean:
        rm -rf $(OBJECTS) $(TARGET)

Last modified: August 02 2004.