目录结构：
WorkSpace/root_dir
|_ SConstruct
|_ multipy
|_ include
|_ mul.h
|_ src
|_ mul.cpp
|_ SConscript
|_ sum
|_ include
|_ sum.h
|_ src
|_ sum.cpp
|_ SConscript
|_ src_main
|_ main.cpp
|_ SConscript
root_dir/SConstruct 的内容：
# This Sconstruct file should build:
# Static and Shared libraries of sum and mul for both release(build/release) and debug mode(build/debug) and place it into the directory as mentioned in parenthesis
# Finally build executable for main.cpp by linking it with sum and mul libraries
# and place it into src_main/build/release and src_main/build/debug directories
import os
env = Environment()
print 'env = ', env
debug_env = env.Clone(CCFLAGS = '-g')
release_env = env.Clone(CCFLAGS = '-O2')
SConscript('sum/src/SConscript', variant_dir='sum/build/debug/', exports ={'env' : debug_env}, duplicate=0)
SConscript('sum/src/SConscript', variant_dir='sum/build/release/', exports = {'env' : release_env}, duplicate=0)
SConscript('multiply/src/SConscript', variant_dir='multiply/build/debug/', exports ={'env' : debug_env}, duplicate=0)
SConscript('multiply/src/SConscript', variant_dir='multiply/build/release/', exports = {'env' : release_env}, duplicate=0)
sum/src/SConscript 文件的内容：
# The main purpose of this SConscript file is to create static and shared library version
# for release and debug mode
# It should also creates objects and place it into build/release and build/debug
# directories inside multiply directory
import os
Import('env')
libs = ['libsum.a', 'libsum.so']
# list of source files
src_list = Glob(os.path.join(Dir('#').abspath, 'sum', 'src', '*.cpp'))
# Path of included files ( - not sure whether it's the correct way to do in scons ?)
env['CPPPATH'] = ['#/sum/include']
env.StaticLibrary(target = 'sum', source = src_list)
env.SharedLibrary(target = 'sum', source = src_list)
Return('libs')
目录中存在类似类型的 SConscript 文件，目的与sum/src/SConscript文件multiply的注释中提到的相同。
对于 src_main/SConscript：
import os
import ('env')
Program('main.cpp', LIBS=['sum', 'mul'], LIBPATHS=[]) # How should I mention LIBPATHS here ?
运行%scons -Q
g++ -o multiply/src/mul.o -c -g -Imultiply/include multiply/src/mul.cpp
ar rc multiply/build/debug/libmul.a multiply/src/mul.o
ranlib multiply/build/debug/libmul.a
g++ -o multiply/src/mul.os -c -g -fPIC -Imultiply/include multiply/src/mul.cpp
g++ -o multiply/build/debug/libmul.so -shared multiply/src/mul.os
ar rc multiply/build/release/libmul.a multiply/src/mul.o
ranlib multiply/build/release/libmul.a
g++ -o multiply/build/release/libmul.so -shared multiply/src/mul.os
g++ -o sum/src/sum.o -c -g -Imultiply/include sum/src/sum.cpp
sum/src/sum.cpp:1:17: fatal error: sum.h: No such file or directory
compilation terminated.
scons: *** [sum/src/sum.o] Error 1
我不明白为什么在创建 sum.o 时使用 -Imultiply/include，尽管对于 sum SConscript 文件我使用了env['CPPPATH'] = ['#/sum/include'] -> 它被视为类似我在 multiply/src/SConscript 文件中使用的那种语句（即env['CPPPATH'] = ['#/multiply/include']）
我是 scons 构建工具的新用户，我无法做这种简单的例子，这是一个非常普遍的实际场景。
请向我建议必要的详细信息以修复我的错误并在我的方法中添加优化以满足要求/目的。