# 第一个例子

myfile:
	echo 'Hello World!' > myfile
# end of file

# 第二个例子

foo.o: foo.c foo.h
	gcc -c foo.c

bar.o: bar.c bar.h
	gcc -c bar.c

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


# 重要语法

## 伪目标

.PHONY: clean

## 变量

### 变量的定义与使用

objects = program.o foo.o utils.o
program : $(objects)
	gcc -o program $(objects)
$(objects) : defs.h

### 目标指定变量

CXXFLAGS := -std=c99 -O2
CXXDFLAGS := -std=c99 -g -Wall
all debug: main
main: main.c
	gcc -o main main.c $(CXXFLAGS)
debug: CXXFLAGS := $(CXXDFLAGS) # 目标指定变量
.PHONY: debug

### 替换引用

foo := a.o b.o c.o
bar := $(foo:.o=.c)
foobar := obj/test.o
test := $(foobar:obj/%.o=%.c)

## 模式规则与自动化变量

CFLAGS := -Wall
%.o %.x : %.c defs.h
	$(CC) $(CFLAGS) $< -o $@
%.x : CFLAGS += -g
%.o : CFLAGS += -O2

## order-only依赖

DIRS := obj bin
$(DIRS):
	mkdir $@
obj/%.o : %.c | obj
	gcc -o $@ -c $<
bin/% : obj/%.o | bin
	gcc -o $@ $<

## 条件语句

info := 0
ifeq ($(MAKECMDGOALS),test)
test: clean
ifneq ($(info),0)
	echo info=1
else
	echo info=0
endif
	echo This is target [test].
clean:
	rm -f bin/*
	rm -f obj/*
endif

## 忽略错误

clean:
	-rmdir obj
	-rmdir bin

## 引用外部文件

Objects := obj/foo.o obj/bar.o
all: $(Objects)
ifneq ($(MAKECMDGOALS),clean)
-include $(Objects:.o=.d)
endif
clean:
	rm -f bin/*
	rm -f obj/*
%.d:
	echo "$(@:.d=.o) : $(@:obj/%.d=%.c)\n\tgcc -c \$$< -o \$$@" > $@



obj/bar.o : bar.c
	gcc -c $< -o $@

# 第三个例子

.
├── debug
│   └── debug.cpp
├── defs.h
├── main.cpp
├── Makefile
└── src
    ├── command.cpp
    ├── file.cpp
    └── utils
        └── utils.cpp



CXX			:= g++
RM			:= rm -f
MKDIR		:= mkdir -p
RMDIR		:= rmdir

CXXFLAGS	:= -std=c++11 -O2
LDFLAGS		:= 
CXXINCLUDE	:= -I.

OBJDIR		:= obj
BINDIR		:= bin

Main		:= $(BINDIR)/main
Header		:= defs.h
Objects		:= $(patsubst ./%.cpp, $(OBJDIR)/%.o, $(shell find . -name '*.cpp'))

Dirs		:= $(BINDIR) $(shell echo $(patsubst %/,%,$(dir $(Objects))) | tr ' ' '\n' | sort -u | tr '\n' ' ')

all: $(Main)

$(OBJDIR)/%.o: %.cpp $(Header) | $(Dirs)
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -c $< -o $@

$(Main): $(Objects) $(Header) | $(Dirs)
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -o $@ $^ $(LDFLAGS)

$(Dirs):
	$(MKDIR) $@

run: $(Main)
	$(Main)

clean:
	$(RM) -r $(OBJDIR)
	$(RM) -r $(BINDIR)

.PHONY: all run clean

# 易错特性

## 变量中的空格

nullstring :=
space := $(nullstring) # end of the line

# 高级用法

## 目录搜寻

VPATH := src:tools:test
test/test.o : test.c
	gcc -c $< -o $@

## 自动生成头文件依赖

Objects := $(wildcard *.cpp)
Objects := $(Objects:.cpp=.o)
all: main
main: $(Objects)
	$(CXX) $(CXXFLAGS) -o $@ $^ $(LDFLAGS)
%.o: %.cpp
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -c $< -o $@
%.d: %.cpp
	set -e; rm -f $@; \
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -MM $< > $@.$$$$; \
	sed 's,\($*\)\.o[ :]*,\1.o $@ : ,g' $@.$$$$ > $@; \
	rm -f $@.$$$$
ifneq ($(MAKECMDGOALS),clean)
-include $(Objects:.o=.d)
endif
clean:
	rm -f *.o *.d main
.PHONY: all clean

# 第四个例子

.
├── main.cpp
├── Makefile
├── src
│   ├── command.cpp
│   ├── command.h
│   ├── console.cpp
│   └── console.h
├── unit_test.cpp
└── utils
    ├── database.cpp
    ├── database.h
    ├── file.cpp
    └── file.h



CXX			:= g++
RM			:= rm -f
MKDIR		:= mkdir -p
RMDIR		:= rmdir
SED			:= sed

CXXFLAGS	:= -std=c++11 -O2
CXXDFLAGS	:= -std=c++11 -g -Wall
LDFLAGS		:= 

VPATH		:= src:utils
CXXINCLUDE	:= $(patsubst %,-I%,$(subst :, ,$(VPATH)))

OBJDIR		:= obj
BINDIR		:= bin
Dirs		:= $(OBJDIR) $(BINDIR)

Main		:= $(BINDIR)/main
Test		:= $(BINDIR)/unit_test

Objects		:= $(patsubst %.cpp, $(OBJDIR)/%.o, $(notdir $(wildcard *.cpp */*.cpp)))

all: $(Main) $(Test)

$(OBJDIR)/%.o: %.cpp | $(Dirs)
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -c $< -o $@

$(OBJDIR)/%.d: %.cpp | $(Dirs)
	@set -e; $(RM) $@; \
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -MM $< > $@.$$$$; \
	$(SED) -i 's,\($*\)\.o[ :]*,\1.o $@ : ,g' $@.$$$$; \
	$(SED) '1s/^/$(OBJDIR)\//' < $@.$$$$ > $@; \
	$(RM) $@.$$$$

ifneq ($(MAKECMDGOALS),clean)
-include $(Objects:.o=.d)
endif

$(Main):	$(filter-out $(OBJDIR)/$(subst $(BINDIR)/,,$(Test).o), $(Objects))
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -o $@ $^ $(LDFLAGS)

$(Test):	$(filter-out $(OBJDIR)/$(subst $(BINDIR)/,,$(Main).o), $(Objects))
	$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -o $@ $^ $(LDFLAGS)

$(Dirs):
	$(MKDIR) $@

debug: CXXFLAGS := $(CXXDFLAGS)
debug: $(Main) $(Test)

run: $(Main)
	$(Main)

test: $(Test)
	$(Test)

clean:
	$(RM) $(OBJDIR)/*.o
	$(RM) $(OBJDIR)/*.d
	$(RM) $(Main)
	$(RM) $(Test)
	-$(RMDIR) $(OBJDIR)
	-$(RMDIR) $(BINDIR)

.PHONY: all debug run test clean

# 其他语法

## 其他函数

dirs := a b c d
files := $(foreach dir,$(dirs),$(wildcard $(dir)/*))

files := $(wildcard a/* b/* c/* d/*)

reverse = $(2) $(1)
foo = $(call reverse,a,b)

## 宏

define mycmd
echo 'compling .cpp to .o using mycmd'
$(CXX) $(CXXFLAGS) $(CXXINCLUDE) -c $< -o $@
endef

%.o: %.cpp
	$(mycmd)