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

Subject: Re: [Boost-users] How to use the optional with property_tree‏
From: 王郁槐 (wyhfly_at_[hidden])
Date: 2013-12-25 01:23:45

Thanks you for your help. Thanks a lot.
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At 2013-12-21 04:28:52,"Sven Steckmann" <spm_boost_at_[hidden]> 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.
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-------- 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;
}
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Olivier TRISTAN
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