Makefile simple induction

Official website ：https://gcc.gnu.org/

file （7.4 edition ）：https://gcc.gnu.org/onlinedocs/7.4.0/

Reference resources ：https://seisman.github.io/how-to-write-makefile/overview.html

1. Basic use

# the first is the final target
main: main.c foo.o bar.o
    gcc main.c foo.o bar.o -o main

foo.o: foo.c
    gcc -c foo.c  
    
bar.o: bar.c
    gcc -c bar.c 

explain ： Final target document main Depend on main.c and func.o, from gcc Generate .func.c equally .

phony

phony False target .Makefile Of target The default is file , and phony The goal of is to execute the program .

Below demo Support make clearall and make clear Instructions .

CC = gcc

main: main.o
	$(CC) main.o -o main
main.o: main.s
	$(CC) -c main.s -o main.o
main.s: main.i
	$(CC) -S main.i -o main.s
main.i: main.c
	$(CC) -E main.c -o main.i

.phony: clean cleanall
clean:
	rm main.i main.s main.o
cleanall:
	rm main.i main.s main.o main

Multiple files can also be generated by using pseudo targets :

all : prog1 prog2 prog3
.PHONY : all

prog1 : prog1.o utils.o
    cc -o prog1 prog1.o utils.o

prog2 : prog2.o
    cc -o prog2 prog2.o

prog3 : prog3.o sort.o utils.o
    cc -o prog3 prog3.o sort.o utils.o

The default target feature is , Always executed , But because of “all” Another false target , The pseudo target is just a tag and will not generate a file , So there won't be “all” Document generation

The rules

2. command

frequently-used echo command , Need to add @, So it doesn't show echo xxx 了 .

exception handling

If there is a command error ,make Will stop . But like mkdir This kind of order , Mistakes should continue , In this case, we can talk about a horizontal bar prefix ：

-mkdir FOO

perhaps make -i.

A semicolon

scene ： The second command runs on the basis of the first instruction

cd /home/hchen; pwd

3. Variable

Specify compiler

If you don't use it one day gcc 了 , The above scripts have to be manually changed one by one . So you can save the compiler as a variable .

assignment ：

• := Normal assignment ;
• = Recursive assignment ;
• += Additional assignment ;
• ?= Conditional assignment , The left side is undefined before assignment ;

CC := g++

main: main.c foo.o
    $(CC) main.c foo.o -o main

foo.o: foo.c
    $(CC) -c foo.c  

Other parameters , Such parameters , The goal is , It is also often used as a variable .

CC := g++
TARGET := main
CFLAGS = -lm -Wall -g
$(TARGET): main.c 
    $(CC) $(CFLAGS) main.c -o main

Built-in variables

Makefile There are some very useful variables ：

• [email protected], Target file ;
• $^, All dependent files
• $<, The first dependency file .
• $*, Target file without extension
• $?, Dependent files whose timestamp is later than the target file

CC := gcc

main: main.o
	$(CC) $^ -o [email protected]

%.o: %.c
	$(CC) -c $^ -o [email protected]

wildcard

#  all .c
objects := $(wildcard *.c)

Target variable

It can be understood as a local variable , It only takes effect in the rules corresponding to the goal .

prog : CFLAGS = -g
prog : prog.o foo.o bar.o
    $(CC) $(CFLAGS) prog.o foo.o bar.o

prog.o : prog.c
    $(CC) $(CFLAGS) prog.c

foo.o : foo.c
    $(CC) $(CFLAGS) foo.c

bar.o : bar.c
    $(CC) $(CFLAGS) bar.c

4. grammar

Conditional statements

ifeq, ifneq

ifeq ($(CC),gcc)
    libs=$(libs_for_gcc)
else
    libs=$(normal_libs)
endif

ifdef

bar =
foo = $(bar)
ifdef foo
    frobozz = yes
else
    frobozz = no
endif

function

demo:

$(subst ee,EE,feet on the street)

5. Other

Some of the parameters

-f Appoint makefile

Compile subdirectories Makefile

subsystem1:
    cd subdir && $(MAKE)
    
subsystem2:
    $(MAKE) -C subdir

$(MAKE) It is a command line with parameters

Conflict situation

If there is main1.c and main2.c Each has one main, Just compile the first .

#  perform 
main1: main1.c func.o
    gcc main1.c foo.o -o main1

#  Don't execute 
main2: main2.c func.o
    gcc main2.c foo.o -o main2

#  perform 
func.o: func.c
    gcc -c func.c  

clean:
    rm *.o main1 main2

Use all You can generate two .

all: main1 main2

main1: main1.c func.o
    gcc main1.c foo.o -o main1

main2: main2.c func.o
    gcc main2.c foo.o -o main2

func.o: func.c
    gcc -c func.c  

clean:
    rm *.o main1 main2