Makefile的使用技巧

Makefile的使用技巧

1、 makefile中的两种变量

Ø COMPILE=$(CC)$(CFLAGS) -c

在使用COMPILE的时候，CC和CFLAGS才会展开，并且是每次都会展开，所以当定义COMPILE的时候，即使CC和CFLAGS还没有值，都没有关系，只要当使用COMPILE时，CC和CFLAGS有值就可以了。

OBJS=$(wildcard *.o)

OBJS每次在引用的时候，获取目标文件的列表，每一次可能都不同，并且每次计算通配符导致运行速度变慢。

Ø COMPILE=：$(CC)$(CFLAGS) -c

在执行这行后，在使用COMPILE时，其值不会再变化，即使CC和CFLAGS变化了。当然可以显示的赋值给COMPILE来改变其值。

2、 使用函数

Ø wildcard

SRCS := $(wildcard *.c)

获得所有的C文件列表

Ø patsubst

OBJS := $(patsubst %.c,%.o,$( wildcard *.c ))

获得所有c文件对应的o文件列表

3、 特殊符号

%.o: %.c

gcc -Wall -c -o $@ $<

将所有的C文件编译成O文件。

4、 两种编译方式

Ø gcc -o myprogram 1.c 2.c

将1.c和2.c编译成myprogram程序。

Ø gcc -c -o 1.o 1.c

将1.c编译成O文件。

5、 依赖性计算

gcc -M init.c > init.d

将所有的依赖文件（包括系统文件）写入d文件

gcc -MM init.c > init.d

将不包括系统文件的依赖文件写入d文件

6、 智能makefile模板

# Lines starting with the pound sign are comments.

#

# This is one of two options you might need to tweak.

EXECUTABLE = myprogram

# You can modify the below as well, but probably

# won't need to.

#

# CC is for the name of the C compiler. CPPFLAGS denotes pre-processor

# flags, such as -I options. CFLAGS denotes flags for the C compiler.

# CXXFLAGS denotes flags for the C++ compiler. You may add additional

# settings here, such as PFLAGS, if you are using other languages such

# as Pascal.

CC = gcc

CPPFLAGS =

CFLAGS = -Wall -O2

CXXFLAGS = $(CFLAGS)

COMPILE = $(CC) $(CPPFLAGS) $(CFLAGS) -c

SRCS := $(wildcard *.c)

OBJS := $(patsubst %.c,%.o,$(SRCS))

DEPS := $(patsubst %.c,%.d,$(SRCS))

# "all" is the default target. Simply make it point to myprogram.

all: $(EXECUTABLE)

# Define the components of the program, and how to link them together.

# These components are defined as dependencies; that is, they must be

# made up-to-date before the code is linked.

#最终的二进制程序依赖于d文件和o文件

$(EXECUTABLE): $(DEPS) $(OBJS)

$(CC) -o $(EXECUTABLE) $(OBJS)

# Specify that the dependency files depend on the C source files.

#生成d文件，d文件内容包括两行，o文件的依赖关系，d文件的依赖关系

%.d: %.c

$(CC) -M $(CPPFLAGS) $< > $@

$(CC) -M $(CPPFLAGS) $< | sed s///.o/.d/ >> $@

# Specify that all .o files depend on .c files, and indicate how

# the .c files are converted (compiled) to the .o files.

#由c文件生成o文件

%.o: %.c

$(COMPILE) -o $@ $<

#删除四类文件

clean:

-rm $(OBJS) $(EXECUTABLE) $(DEPS) *~

explain:

@echo "The following information represents your program:"

@echo "Final executable name: $(EXECUTABLE)"

@echo "Source files: $(SRCS)"

@echo "Object files: $(OBJS)"

@echo "Dependency files: $(DEPS)"

depend: $(DEPS)

@echo "Dependencies are now up-to-date."

#将d文件内容导入makefile中

-include $(DEPS)

特点：

Ø 没有出现任何一个具体的文件名

Ø 采用依赖性文件确定依赖关系，并最后通过include将依赖关系导入

Ø 最终的二进制程序，不仅仅依赖于o文件，还依赖于d文件

具体见example4

7、 级联嵌套makefile

# Lines starting with the pound sign are comments.

#

# This is one of two options you might need to tweak.

EXECUTABLE = myprogram

# You can modify the below as well, but probably

# won't need to.

#

# CC is for the name of the C compiler. CPPFLAGS denotes pre-processor

# flags, such as -I options. CFLAGS denotes flags for the C compiler.

# CXXFLAGS denotes flags for the C++ compiler. You may add additional

# settings here, such as PFLAGS, if you are using other languages such

# as Pascal.

CC = gcc

CPPFLAGS =

CFLAGS = -Wall -O2

CXXFLAGS = $(CFLAGS)

COMPILE = $(CC) $(CPPFLAGS) $(CFLAGS) -c

SRCS := $(wildcard *.c)

OBJS := $(patsubst %.c,%.o,$(SRCS))

DEPS := $(patsubst %.c,%.d,$(SRCS))

DIRS= input format

# "all" is the default target. Simply make it point to myprogram.

all: $(EXECUTABLE)

subdirs:

@for dir in $(DIRS); do $(MAKE) -C $$dir; done

# Define the components of the program, and how to link them together.

# These components are defined as dependencies; that is, they must be

# made up-to-date before the code is linked.

$(EXECUTABLE): subdirs $(DEPS) $(OBJS)

$(CC) -o $(EXECUTABLE) $(OBJS)

# Specify that the dependency files depend on the C source files.

%.d: %.c

$(CC) -M $(CPPFLAGS) $< > $@

$(CC) -M $(CPPFLAGS) $< | sed s///.o/.d/ >> $@

# Specify that all .o files depend on .c files, and indicate how

# the .c files are converted (compiled) to the .o files.

%.o: %.c

$(COMPILE) -o $@ $<

clean:

-rm $(OBJS) $(EXECUTABLE) $(DEPS) *~

@for dir in $(DIRS); do $(MAKE) -C $$dir clean; done

explain:

@echo "The following information represents your program:"

@echo "Final executable name: $(EXECUTABLE)"

@echo "Source files: $(SRCS)"

@echo "Object files: $(OBJS)"

@echo "Dependency files: $(DEPS)"

@echo "Subdictionary: $(DIRS)"

depend: $(DEPS)

@for dir in $(DIRS); do $(MAKE) -C $$dir; done

@echo "Dependencies are now up-to-date."

-include $(DEPS)

这是顶层makefile相对于标准智能模板进行的修改，input和format中的makefile为标准的模块。