问题描述
我已经尝试了太多时间，无法从boost库中访问json_reader ptree.
I have been trying for too much time now, to access a json_reader ptree from the boost library.
我有一个经常封装的json文件:(pseudo-json:)
I have a json file that is capsulated really often: (pseudo-json:)
"Foo": {
"nameofFoo:"foofoo"
"Bar": [{
"BarFoo":
{ BarFooDeep: {
BarFooDeepDeep: {
"BarFooValue1": 123
"BarFooValue2" : 456
}
}
}
"FooBar": [ {
"FooBarDeep" :[ {
FooBarDeepDeep:[ {
FooBarValue1: "ineedthis"
FooBarValue2: "andthis"
} ]
FooBarDeepDeep1:[ {
FooBarValue1: "ineedthis"
FooBarValue2: "andthis"
} ]
"FooBarDeep" :[ {
FooBarDeepDeep2:[ {
FooBarValue1: "ineedthis"
FooBarValue2: "andthis"
} ]
FooBarDeepDeep3:[ {
FooBarValue1: "ineedthis"
FooBarValue2: "andthis"
} ]
and so on .... won t complete this now...
现在我只需要获取所有FooBar的FooBarValue1和FooBarValue2.
Now I only need to get FooBarValue1 and FooBarValue2 of all FooBar.
我知道ptree将数组与空子元素(")放在一起
I know ptree puts arrays together with empty childs ("")
我可以通过递归地遍历所有子项来访问所有成员.
I can access all the members by itereration over all the childs recursively.
但是没有更好的方法来访问特殊值吗?
But is there not a better way to access special values?
ptree如何找到有效的方法?我总是会收到编译器错误...
how does ptree find works? i always get compiler errors ...
ptree jsonPT;
read_json( JSON_PATH, jsonPT);
ptree::const_iterator myIT = jsonPT.find("FooBarValue1");
double mlat = boost::lexical_cast<int>(myIT->second.data());
任何人都可以给我一个有用的提示，告诉您如何访问此ptree吗?！?
Can anyone give me a useful hint how to get access to this ptree?!?
推荐答案
正如链接答案中所暗示的，我评论了(Boost.PropertyTree子路径处理)，您可以编写自己的选择器"查询，因此可以编写以下内容:
As hinted in the linked answer I commented (Boost.PropertyTree subpath processing), you could write your own "selector" query, so you could write stuff like:
read_json("input.txt", pt);
std::ostream_iterator<std::string> out(std::cout, ", ");
std::cout << "\nSpecific children but in arrays: ";
enumerate_path(pt, "Foo.Bar..FooBar..FooBarDeep1..FooBarDeepDeep6..FooBarValue2", out);
std::cout << "\nSingle wildcard: ";
enumerate_path(pt, "Foo.Bar..FooBar..FooBarDeep1..*..FooBarValue2", out);
std::cout << "\nTwo wildcards: ";
enumerate_path(pt, "Foo.Bar..FooBar..*..*..FooBarValue2", out);
enumerate_path函数不必太复杂，不需要任何输出迭代器(因此您也可以back_inserter(some_vector)):
The enumerate_path function need not be too complicated and takes any output iterator (so you can back_inserter(some_vector) just as well):
template <typename Tree, typename Out, typename T = std::string>
Out enumerate_path(Tree const& pt, typename Tree::path_type path, Out out) {
if (path.empty())
return out;
if (path.single()) {
*out++ = pt.template get<T>(path);
} else {
auto head = path.reduce();
for (auto& child : pt) {
if (head == "*" || child.first == head) {
out = enumerate_path(child.second, path, out);
}
}
}
return out;
}
作为简单的演示作品打印:
As simple working demo prints:
Specific children but in arrays: andthis6,
Single wildcard: andthis6, andthis7, andthis8, andthis9,
Two wildcards: andthis1, andthis2, andthis3, andthis4, andthis6, andthis7, andthis8, andthis9,
具有以下 input.txt :
{
"Foo": {
"nameofFoo": "foofoo",
"Bar": [{
"BarFoo": {
"BarFooDeep": {
"BarFooDeepDeep": {
"BarFooValue1": 123,
"BarFooValue2": 456
}
}
},
"FooBar": [{
"FooBarDeep0": [{
"FooBarDeepDeep1": [{
"FooBarValue1": "ineedthis1",
"FooBarValue2": "andthis1"
}],
"FooBarDeepDeep2": [{
"FooBarValue1": "ineedthis2",
"FooBarValue2": "andthis2"
}]
},
{
"FooBarDeepDeep3": [{
"FooBarValue1": "ineedthis3",
"FooBarValue2": "andthis3"
}],
"FooBarDeepDeep4": [{
"FooBarValue1": "ineedthis4",
"FooBarValue2": "andthis4"
}]
}],
"FooBarDeep1": [{
"FooBarDeepDeep6": [{
"FooBarValue1": "ineedthis6",
"FooBarValue2": "andthis6"
}],
"FooBarDeepDeep7": [{
"FooBarValue1": "ineedthis7",
"FooBarValue2": "andthis7"
}]
},
{
"FooBarDeepDeep8": [{
"FooBarValue1": "ineedthis8",
"FooBarValue2": "andthis8"
}],
"FooBarDeepDeep9": [{
"FooBarValue1": "ineedthis9",
"FooBarValue2": "andthis9"
}]
}]
}]
}]
}
}
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <iostream>
template <typename Tree, typename Out, typename T = std::string>
Out enumerate_path(Tree const& pt, typename Tree::path_type path, Out out) {
if (path.empty())
return out;
if (path.single()) {
*out++ = pt.template get<T>(path);
} else {
auto head = path.reduce();
for (auto& child : pt) {
if (head == "*" || child.first == head) {
out = enumerate_path(child.second, path, out);
}
}
}
return out;
}
int main() {
std::ostream_iterator<std::string> out(std::cout, ", ");
using namespace boost::property_tree;
ptree pt;
read_json("input.txt", pt);
std::cout << "\nSpecific children but in arrays: ";
enumerate_path(pt, "Foo.Bar..FooBar..FooBarDeep1..FooBarDeepDeep6..FooBarValue2", out);
std::cout << "\nSingle wildcard: ";
enumerate_path(pt, "Foo.Bar..FooBar..FooBarDeep1..*..FooBarValue2", out);
std::cout << "\nTwo wildcards: ";
enumerate_path(pt, "Foo.Bar..FooBar..*..*..FooBarValue2", out);
}
这篇关于boost :: ptree找到了吗?或如何访问深层阵列? C ++的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！