scons实践笔记（2）－－带选项的编译

（1）如果想要生成两个编译器版本的代码，比如在PC机上的GCC编译和ARM linux gcc交叉编译，并且在编译的时候可以选择，SConstruct内容如下，源代码测试文件还是前一个hello world程序：

> vim SConstruct

src = Glob('*.c')

platform = ARGUMENTS.get('platform','pc')

if platform == 'arm':

EXE_PATH = '/opt/arm-2007q1/bin'
PREFIX = 'arm-none-linux-gnueabi-'
ARMCC = PREFIX + 'gcc'
ARMAS = PREFIX + 'gcc'
ARMAR = PREFIX + 'ar'
ARMLINK = PREFIX + 'gcc'
ARMSIZE = PREFIX + 'size'
ARMOBJDUMP = PREFIX + 'objdump'
ARMOBJCPY = PREFIX + 'objcpy'

env = Environment (AS = ARMAS,
CC = ARMCC,
AR = ARMAR,
LINK = ARMLINK)
env.PrependENVPath ('PATH',EXE_PATH)

elif platform == 'pc':
env = Environment()
else:
pass

env.Program(source = src, target = 'hello_world')

第二条语句指定了若platform缺省时为pc，故执行scons 与scons platform=pc效果一样。运行如下：

> ls
main.c  SConstruct

> scons platform=arm
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
arm-none-linux-gnueabi-gcc -o main.o -c main.c
arm-none-linux-gnueabi-gcc -o hello_world main.o
scons: done building targets.

> scons platform=pc
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o main.o -c main.c
gcc -o hello_world main.o
scons: done building targets.

> scons -c
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed main.o
Removed hello_world
scons: done cleaning targets.

> scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o main.o -c main.c
gcc -o hello_world main.o
scons: done building targets.

（2）同样，这个方法还可以用来编译器生成不同版本的代码（如release版本和debug版本），如下：

> vim SConstruct

src = Glob('*.c')
debug = ARGUMENTS.get('debug',0)
vars = Variables(None,ARGUMENTS)
vars.Add('debug','Set to 1 to build for debug', 0)
env = Environment(variables = vars)
Help(vars.GenerateHelpText(env))

if int(debug) == 1:
env.Append( CCFLAGS = '-g')

env.Program(source = src, target = 'hello_world')

> ls
main.c  SConstruct

> scons debug=1
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o main.o -c -g main.c
gcc -o hello_world main.o
scons: done building targets.

> scons debug=0
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o main.o -c main.c
gcc -o hello_world main.o
scons: done building targets.

这样，便可控制debug版本和release版本的生成，另外SConstruct 脚本中第3、4、5、6句用来产生帮助信息，可以加上-h参数以运行使用：

> scons -h
scons: Reading SConscript files ...
scons: done reading SConscript files.

debug: Set to 1 to build for debug
default: 0
actual: 0

Use scons -H for help about command-line options.

这样便可提示用户使用命令。

（3）变量（如debug=1，platform=pc）还可以从文件中引入，详细在用户手册（10.2.3. Reading Build Variables From a File）一节，预编译定义也可由这种方法定义