Re: [Boost-users] How to use the optional with property_tree‏

Subject: Re: [Boost-users] How to use the optional with property_tree‏
From: Sven Steckmann (spm_boost_at_[hidden])
Date: 2013-12-20 15:28:52

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<o.tristan_at_[hidden]>
> 时间：周四 12月19日 22:08
> 收件人：boost-users_at_[hidden]
> 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;
>>> }
>>>
>>>
>>>
>>>
>>> --
>>> 兰生幽谷, ä¸ä»¥æ— äººè€Œä¸èŠ³...
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Boost-users mailing list
>>> Boost-users_at_[hidden]
>>> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>> -- 
>> Olivier TRISTAN
>> uvi.net
>>
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