C++ Boost 1.46.1，属性树：如何迭代接收子 ptree 的 ptree？
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Boost 1.46.1, Property Tree: How to iterate through ptree receiving sub ptrees?
提问by Rella
First of all I shall say that I think I got how it should be done but my code will not compile any way I try. I based my assumption on this official example of empty ptree trick. There you can find next line:
首先，我想说我想我知道应该怎么做，但我的代码不会以我尝试的任何方式编译。我的假设基于这个空 ptree 技巧的官方示例。在那里你可以找到下一行：
const ptree &settings = pt.get_child("settings", empty_ptree<ptree>());
Which shows that it is (or should be) possible to get subptree out from ptree.
这表明可以（或应该）从 ptree 中取出 subptree。
So I assumed we could iterate thru ptree with something like BOOST_FOREACHin such manner:
所以我假设我们可以用BOOST_FOREACH这样的方式遍历 ptree ：
BOOST_FOREACH(const boost::property_tree::ptree &v,
config.get_child("servecies"))
{
}
But I get next error:
但我得到下一个错误：
Error 1 error C2440: 'initializing' : cannot convert from 'std::pair<_Ty1,_Ty2>' to 'const boost::property_tree::ptree &'
错误 1 错误 C2440：“正在初始化”：无法从“std::pair<_Ty1,_Ty2>”转换为“const boost::property_tree::ptree &”
or if I try
或者如果我尝试
BOOST_FOREACH(boost::property_tree::ptree &v,
config.get_child("servecies", boost::property_tree::empty_ptree<boost::property_tree::ptree>()))
{
}
I get:
我得到：
Error 1 error C2039: 'empty_ptree' : is not a member of 'boost::property_tree'
错误 1 错误 C2039：“empty_ptree”：不是“boost::property_tree”的成员
So what shall I do: how to iterate thru Boost Ptree and get sub Ptrees?
那么我该怎么办：如何遍历 Boost Ptree 并获得子 Ptree？
Update:I also tried such code
更新：我也试过这样的代码
BOOST_FOREACH(boost::property_tree::ptree::value_type &v,
config.get_child("path.to.array_of_objects"))
{
std::cout << "First data: " << v.first.data() << std::endl;
boost::property_tree::ptree subtree = (boost::property_tree::ptree) v.second ;
BOOST_FOREACH(boost::property_tree::ptree::value_type &vs,
subtree)
{
std::cout << "Sub data: " << vs.first.data() << std::endl;
}
}
This compiles, does not throw any exeptions but does not cout any Sub data, it just skeeps thru this cycle.
这会编译，不会抛出任何Sub data异常，但不会抛出任何异常，它只是通过这个循环。
Update 2:
更新 2：
Hm... something probably went wrong in my xml - now I get correct results with that code.
嗯...我的 xml 中可能出了点问题 - 现在我用该代码得到了正确的结果。
回答by antonakos
The property tree iterators point to pairs of the form (key, tree)of type ptree::value_type. The standard loop for iterating through the children of the node at paththerefore looks like:
属性树迭代器指向(key, tree)type形式的对ptree::value_type。因此，迭代节点子节点的标准循环path如下所示：
BOOST_FOREACH(const ptree::value_type &v, pt.get_child(path)) {
// v.first is the name of the child.
// v.second is the child tree.
}
回答by Ela782
Using C++11, you can use the following to iterate through all the children of the node at path:
使用 C++11，您可以使用以下命令遍历节点的所有子节点path：
ptree children = pt.get_child(path);
for (const auto& kv : children) {
// kv is of type ptree::value_type
// kv.first is the name of the child
// kv.second is the child tree
}
回答by Evalds Urtans
I had the same problem with iterating trough JSON sub nodes
我在遍历 JSON 子节点时遇到了同样的问题
boost::property_tree::read_json(streamJSON, ptJSON);
If you have a structure like:
如果你有这样的结构：
{
playlists: [ {
id: "1",
x: "something"
shows: [
{ val: "test" },
{ val: "test1" },
{ val: "test2" }
]
},
{
id: "2"
x: "else",
shows: [
{ val: "test3" }
]
}
]
}
You can iterate trough child nodes like this:
您可以像这样遍历子节点：
BOOST_FOREACH(boost::property_tree::ptree::value_type &playlist, ptJSON.get_child("playlists"))
{
unsigned long uiPlaylistId = playlist.second.get<unsigned long>("id");
BOOST_FOREACH(boost::property_tree::ptree::value_type &show, playlist.second.get_child("shows."))
{
std::string strVal = show.second.get<std::string>("val");
}
}
I could not find anything about path selector "shows." to select sub array. (notice the dot at the end)
我找不到有关路径选择器“显示”的任何信息。选择子数组。（注意末尾的点）
Some good documentation can be found here: http://kaalus.atspace.com/ptree/doc/index.html
一些好的文档可以在这里找到：http: //kaalus.atspace.com/ptree/doc/index.html
Hope this helps someone.
希望这可以帮助某人。
