Thanks you for your help. Thanks a lot. -- 兰生幽谷, 不以无人而不芳... At 2013-12-21 04:28:52,"Sven Steckmann" wrote: Hi, You can access child2 only, if the child2 is true, otherwise you have no child2. An optional returns false if there is no value inside, then it is like a NULL pointer. Merry Christmas! On 19.12.2013 15:28, 王郁槐 wrote: I still don't understand，could you please figure it out？thanks. 发送自魅族手机 -------- 原始邮件 -------- 发件人：Olivier Tristan 时间：周四 12月19日 22:08 收件人：boost-users@lists.boost.org 主题：Re: [Boost-users] How to use the optional with property_tree‏ Those following lines from your code should give you a hint if (child2) { child2.get().put_value(strValue); } else { child2.get().put_value(strValue); } Le 19/12/2013 12:34, 王郁槐 a écrit : Could anyone help? Why the below code will crash on the below line? I'm using the boost property_tree. Thanks. child1.get().put(sub_field, strValue); ========================================================= #include <fstream> #include #include #include #include #include void writeConfig(const std::string &field, const std::string &sub_field, const std::string & strValue) { if (!boost::filesystem::exists(prog_cfg_file)) { std::ofstream ofIniConfig(prog_cfg_file, std::ofstream::out|std::ofstream::app); ofIniConfig.close(); } boost::property_tree::ptree pt; boost::property_tree::ini_parser::read_ini(prog_cfg_file, pt); boost::optionalboost::property_tree::ptree& child1 = pt.get_child_optional(field); if (child1) { boost::optionalboost::property_tree::ptree& child2 = child1.get().get_child_optional(sub_field); if (child2) { child2.get().put_value(strValue); }else { child2.get().put_value(strValue); } }else { child1.get().put(sub_field, strValue); } boost::property_tree::ini_parser::write_ini(prog_cfg_file, pt); } int main() { writeConfig("test", "a", "OK"); return 0; } -- 兰生幽谷, 不以无人而不芳... _______________________________________________ Boost-users mailing list Boost-users@lists.boost.orghttp://lists.boost.org/mailman/listinfo.cgi/boost-users -- Olivier TRISTAN uvi.net _______________________________________________ Boost-users mailing list Boost-users@lists.boost.orghttp://lists.boost.org/mailman/listinfo.cgi/boost-users _______________________________________________ Boost-users mailing list Boost-users@lists.boost.orghttp://lists.boost.org/mailman/listinfo.cgi/boost-users