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.
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-------- 原始邮件 -------- 发件人：Olivier Tristan<o.tristan@uvi.net> 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 <boost/filesystem.hpp> #include <boost/property_tree/ptree.hpp> #include <boost/property_tree/ini_parser.hpp> #include <boost/any.hpp> #include <boost/optional.hpp>
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::optional<boost::property_tree::ptree&> child1 = pt.get_child_optional(field);
if (child1) { boost::optional<boost::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; }
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