blocks|key|4336692|text|get_child+(以及所有其他基于路径的访问函数)不太擅长处理多个相同的键。它将选择具有给定密钥的第一个子级，并返回该子级，忽略所有其他子级。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4336693|但是您不需要get_child，因为您已经掌握了您想要的节点。|4336694|pt.get_child("applications")会给你一个ptree。对其进行迭代会得到一个ptree::value_type，这是一个std::pair<std::string,+ptree>。|4336695|那么，第一件奇怪的事情就是这一行：|4336696|std::string+key+=+v.first.data();|code-block|syntax|javascript|4336697|您在这里调用的data()函数是std::string::data，而不是ptree::data。你可以直接写|4336698|std::string+key+=+v.first;|4336699|下一个奇怪的事情是比较：|4336700|if+(key+==+std::string("application"))|4336701|您不需要在这里显式地构造std::string。实际上，这样做是悲观的，因为当std::string具有用于C样式字符串的比较运算符时，它必须分配一个字符串缓冲区并将字符串复制到那里。|4336702|然后在pt.get_child("applications.application")上迭代，但不需要执行这种查找-+v.second已经是您想要的树了。|4336703|此外，您根本不需要遍历该子对象，您可以使用它的查找函数来获取所需的内容。|4336704|std::string+pkgId+=+v.second.get("id",+"");|4336705|总而言之，这是我要写的代码：|4336706|boost::property_tree::ptree+pt;
boost::property_tree::read_xml(sModel,+pt);

BOOST_FOREACH(boost::property_tree::ptree::value_type+&v,+pt.get_child("applications"))
{
++++//+You+can+even+omit+this+check+if+you+can+rely+on+all+children
++++//+being+application+nodes.
++++if+(v.first+==+"application")
++++{
++++++++std::string+pkgId+=+v.second.get("id",+"");
++++++++std::string+platform+=+v.second.get("platform",+"");
++++++++std::string+version+=+v.second.get("version",+"");
++++}
}|4336707|entityMap^0|0|9|0|6|9|0|0|S|X|5|1E|H|20|T|0|0|0|7|6|G|H|11|B|0|0|0|0|C|B|13|B|0|3|14|1N|8|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1I|8|@$9|1J|A|1K|B|C]|$9|1L|A|1M|B|C]|$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1R|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1S|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1T|8|@$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]|$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|S|3|T|5|N|7|20|8|@]|D|@]|E|$O|P]]|$1|U|3|V|5|6|7|21|8|@]|D|@]|E|$]]|$1|W|3|X|5|N|7|22|8|@]|D|@]|E|$O|P]]|$1|Y|3|Z|5|6|7|23|8|@$9|24|A|25|B|C]|$9|26|A|27|B|C]]|D|@]|E|$]]|$1|10|3|11|5|6|7|28|8|@$9|29|A|2A|B|C]|$9|2B|A|2C|B|C]]|D|@]|E|$]]|$1|12|3|13|5|6|7|2D|8|@]|D|@]|E|$]]|$1|14|3|15|5|N|7|2E|8|@]|D|@]|E|$O|P]]|$1|16|3|17|5|6|7|2F|8|@]|D|@]|E|$]]|$1|18|3|19|5|N|7|2G|8|@]|D|@]|E|$O|P]]|$1|1A|3|-4|5|6|7|2H|8|@]|D|@]|E|$]]]|1B|$]]

<code>get_child</code> (and all the other path-based access functions) isn't very good at dealing with multiple identical keys. It will choose the first child with the given key and return that, ignoring all others.

But you don't need <code>get_child</code>, because you already hold the node you want in your hand.

<code>pt.get_child("applications")</code> gives you a <code>ptree</code>. Iterating over that gives you a <code>ptree::value_type</code>, which is a <code>std::pair&lt;std::string, ptree&gt;</code>.

The first weird thing, then, is this line:

<pre><code>std::string key = v.first.data();
</code></pre>

The <code>data()</code> function you're calling here is <code>std::string::data</code>, not <code>ptree::data</code>. You could just write

<pre><code>std::string key = v.first;
</code></pre>

The next strange thing is the comparison:

<pre><code>if (key == std::string("application"))
</code></pre>

You don't need to explicitly construct a <code>std::string</code> here. In fact, doing so is a pessimization, because it has to allocate a string buffer and copy the string there, when <code>std::string</code> has comparison operators for C-style strings.

Then you iterator over <code>pt.get_child("applications.application")</code>, but you don't need to do this lookup - <code>v.second</code> is already the tree you want.

Furthermore, you don't need to iterate over the child at all, you can use its lookup functions to get what you need.

<pre><code>std::string pkgId = v.second.get("id", "");
</code></pre>

So to sum up, this is the code I would write:

<pre><code>boost::property_tree::ptree pt;
boost::property_tree::read_xml(sModel, pt);

BOOST_FOREACH(boost::property_tree::ptree::value_type &amp;v, pt.get_child("applications"))
{
 // You can even omit this check if you can rely on all children
 // being application nodes.
 if (v.first == "application")
 {
 std::string pkgId = v.second.get("id", "");
 std::string platform = v.second.get("platform", "");
 std::string version = v.second.get("version", "");
 }
}
</code></pre>

blocks|key|4336720|text|检查此示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4336721|#include+<boost/property_tree/xml_parser.hpp>
#include+<boost/property_tree/ptree.hpp>
#include+<boost/foreach.hpp>

struct+Application
{
++++int++++++++++m_id
++++std::string++m_platform;
++++float++++++++m_version;
};

typedef+std::vector<Application>+AppList;

AppList+Read()
{
++++using+boost::property_tree::ptree;

++++//+Populate+tree+structure+(pt):

++++ptree+pt;
++++read_xml("applications.xml",+pt);+//+For+example.

++++//+Traverse+pt:

++++AppList+List;
++++BOOST_FOREACH(ptree::value_type+const&+v,+pt.get_child("applications"))
++++{
++++++++if+(v.first+==+"application")
++++++++{
++++++++++++Application+App;
++++++++++++App.id+=+v.second.get<int>("id");
++++++++++++App.platform+=+v.second.get<std::string>("platform");
++++++++++++App.version+=+v.second.get<float>("version");

++++++++++++List.push_back(App);
++++++++}
++++}

++++return+List;
}|code-block|syntax|javascript|4336722|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Check this example:

<pre><code>#include &lt;boost/property_tree/xml_parser.hpp&gt;
#include &lt;boost/property_tree/ptree.hpp&gt;
#include &lt;boost/foreach.hpp&gt;

struct Application
{
 int m_id
 std::string m_platform;
 float m_version;
};

typedef std::vector&lt;Application&gt; AppList;

AppList Read()
{
 using boost::property_tree::ptree;

 // Populate tree structure (pt):

 ptree pt;
 read_xml("applications.xml", pt); // For example.

 // Traverse pt:

 AppList List;
 BOOST_FOREACH(ptree::value_type const&amp; v, pt.get_child("applications"))
 {
 if (v.first == "application")
 {
 Application App;
 App.id = v.second.get&lt;int&gt;("id");
 App.platform = v.second.get&lt;std::string&gt;("platform");
 App.version = v.second.get&lt;float&gt;("version");

 List.push_back(App);
 }
 }

 return List;
}
</code></pre>

I have following xml data and i want to parse through boost xml parser.

<pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;applications&gt;
 &lt;application&gt;
 &lt;id&gt;1&lt;/id&gt;
 &lt;platform&gt;linux-x64&lt;/platform&gt;
 &lt;version&gt;2.4&lt;/version&gt;
 &lt;/application&gt;
 &lt;application&gt;
 &lt;id&gt;2&lt;/id&gt;
 &lt;platform&gt;windows&lt;/platform&gt;
 &lt;version&gt;2.5&lt;/version&gt;
 &lt;/application&gt;
 &lt;application&gt;
 &lt;id&gt;3&lt;/id&gt;
 &lt;platform&gt;linux&lt;/platform&gt;
 &lt;version&gt;2.6&lt;/version&gt;
 &lt;/application&gt;
&lt;/applications&gt;
</code></pre>

I have written below boost code but I read only first child of "applications" and not able to read other two childs. Everytime inner loop get the data of first child.

<pre><code>boost::property_tree::ptree pt;
boost::property_tree::read_xml(sModel, pt); // sModel is filename which contains above xml data

BOOST_FOREACH(boost::property_tree::ptree::value_type &amp;v, pt.get_child("applications"))
{
 std::string key = v.first.data(); 
 std::string Id, platform, version;

 if (key == std::string("application"))
 {
 BOOST_FOREACH(boost::property_tree::ptree::value_type &amp;v_, pt.get_child("applications.application"))
 {
 std::string app_key = v_.first.data();
 std::string app_value = v_.second.data();

 if (app_key == std::string("id"))
 pkgId = app_value;
 else if (app_key == std::string("platform"))
 platform = app_value;
 else if (app_key == std::string("version"))
 version = app_value;
 }
 }
}
</code></pre>

Here, every time i get the platform as "linux-x64".
Can someone guide how to read all the child through this boost xml ?

Thanks in Advance.

Boost and xml parsing

我有以下xml数据，我想通过boost xml解析器进行解析。<?xml version="1.0" encoding="UTF-8"?><applications> <application> <id>1</id> <platform>linux-x64</platf...

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