与升压解析XML属性 [英] Parsing XML Attributes with Boost

问题描述

我想与大家分享，同时试图处理从C ++与Boost库（版本1.52.0）的XML元素的一些属性，我有一个问题。鉴于以下code：

I would like to share with you an issue I'm having while trying to process some attributes from XML elements in C++ with Boost libraries (version 1.52.0). Given the following code:

#define ATTR_SET ".<xmlattr>"
#define XML_PATH1 "./pets.xml"

#include <iostream>
#include <string>
#include <boost/foreach.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>

using namespace std;
using namespace boost;
using namespace boost::property_tree;

const ptree& empty_ptree(){
    static ptree t;
    return t;
}

int main() {
    ptree tree;
    read_xml(XML_PATH1, tree);
    const ptree & formats = tree.get_child("pets", empty_ptree());
    BOOST_FOREACH(const ptree::value_type & f, formats){
        string at = f.first + ATTR_SET;
        const ptree & attributes = formats.get_child(at, empty_ptree());
        cout << "Extracting attributes from " << at << ":" << endl;
        BOOST_FOREACH(const ptree::value_type &v, attributes){
            cout << "First: " << v.first.data() << " Second: " << v.second.data() << endl;
        }
    }
}

让我们说我有以下XML结构：

Let's say I have the following XML structure:

<?xml version="1.0" encoding="utf-8"?>
<pets>
    <cat name="Garfield" weight="4Kg">
        <somestuff/>
    </cat>
    <dog name="Milu" weight="7Kg">
        <somestuff/>
    </dog>
    <bird name="Tweety" weight="0.1Kg">
        <somestuff/>
    </bird>
</pets>

因此​​，控制台输出，我会得到的将是下一个：

Therefore, the console output I'll get will be the next:

Extracting attributes from cat.<xmlattr>:
First: name Second: Garfield
First: weight Second: 4Kg
Extracting attributes from dog.<xmlattr>:
First: name Second: Milu
First: weight Second: 7Kg
Extracting attributes from bird.<xmlattr>:
First: name Second: Tweety
First: weight Second: 0.1Kg

但是，如果我决定使用一个共同的结构为每一个​​元件从根节点铺设（以便从它们的特定属性识别它们），其结果将完全改变。这可能是在这种情况下，XML文件：

However, if I decide to use a common structure for every single element laying down from the root node (in order to identify them from their specific attributes), the result will completely change. This may be the XML file in such case:

<?xml version="1.0" encoding="utf-8"?>
<pets>
    <pet type="cat" name="Garfield" weight="4Kg">
        <somestuff/>
    </pet>
    <pet type="dog" name="Milu" weight="7Kg">
        <somestuff/>
    </pet>
    <pet type="bird" name="Tweety" weight="0.1Kg">
        <somestuff/>
    </pet>
</pets>

和输出将是如下：

Extracting attributes from pet.<xmlattr>:
First: type Second: cat
First: name Second: Garfield
First: weight Second: 4Kg
Extracting attributes from pet.<xmlattr>:
First: type Second: cat
First: name Second: Garfield
First: weight Second: 4Kg
Extracting attributes from pet.<xmlattr>:
First: type Second: cat
First: name Second: Garfield
First: weight Second: 4Kg

似乎被正确识别从根结点悬挂元件的数量，因为已经打印三套属性。然而，所有这些参考的第一元素的属性...

It seems the number of elements hanging from the root node is being properly recognized since three sets of attributes have been printed. Nevertheless, all of them refer to the attributes of the very first element...

我不是在C专家++和真正的新提升，所以这可能是什么我就缺少哈希映射处理或使...任何意见将大大AP preciated。

I'm not an expert in C++ and really new to Boost, so this might be something I'm missing with respect to hash mapping processing or so... Any advice will be much appreciated.

推荐答案

与你的程序的问题是位于此行：

The problem with your program is located in this line:

const ptree & attributes = formats.get_child(at, empty_ptree());

这条线，你是要求得到孩子宠物＆LT; xmlattr＆GT; 从宠物和你做独立取其这3次˚F你遍历。继这篇文章我猜你需要什么使用的是：

With this line you are asking to get the child pet.<xmlattr> from pets and you do this 3 times independently of whichever f you are traversing. Following this article I'd guess that what you need to use is:

const ptree & attributes = f.second.get_child("<xmlattr>", empty_ptree());

满code，这与两个XML文件的工作原理是：

The full code, that works with both your xml files, is:

#define ATTR_SET ".<xmlattr>"
#define XML_PATH1 "./pets.xml"

#include <iostream>
#include <string>
#include <boost/foreach.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>

using namespace std;
using namespace boost;
using namespace boost::property_tree;

const ptree& empty_ptree(){
    static ptree t;
    return t;
}

int main() {
    ptree tree;
    read_xml(XML_PATH1, tree);
    const ptree & formats = tree.get_child("pets", empty_ptree());
    BOOST_FOREACH(const ptree::value_type & f, formats){
        string at = f.first + ATTR_SET;
        const ptree & attributes = f.second.get_child("<xmlattr>", empty_ptree());
        cout << "Extracting attributes from " << at << ":" << endl;
        BOOST_FOREACH(const ptree::value_type &v, attributes){
            cout << "First: " << v.first.data() << " Second: " << v.second.data() << endl;
        }
    }
}

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