def select_toolchain_version():
    '''Because ndk-r8e uses gcc4.6 as default. gcc4.6 doesn't support c++11. So we should select gcc4.7 when
    using ndk-r8e. But gcc4.7 is removed in ndk-r9,so we should determine whether gcc4.7 exist.
    Conclution:
    ndk-r8e  -> use gcc4.7
    ndk-r9   -> use gcc4.8
    '''

    ndk_root = check_environment_variables()
    if os.path.isdir(os.path.join(ndk_root,"toolchains/arm-linux-androideabi-4.9")):
        os.environ['NDK_TOOLCHAIN_VERSION'] = 4.9'
        print The Selected NDK toolchain version was 4.9 !"
    elif os.path.isdir(os.path.join(ndk_root,0); line-height:1.5!important">toolchains/arm-linux-androideabi-4.84.8The Selected NDK toolchain version was 4.8 !toolchains/arm-linux-androideabi-4.74.7The Selected NDK toolchain version was 4.7 !else:
        Couldn't find the gcc toolchain."
        exit(1)