18

我想与您分享一个我在尝试使用 Boost 库（版本 1.52.0）处理 C++ 中 XML 元素的某些属性时遇到的问题。给定以下代码：

#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;
        }
    }
}

假设我有以下 XML 结构：

<?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，我将得到的控制台输出将是下一个：

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，如果我决定为从根节点放下的每个元素使用一个通用结构（以便从它们的特定属性中识别它们），结果将完全改变。在这种情况下，这可能是 XML 文件：

<?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>

输出如下：

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

由于已经打印了三组属性，因此似乎可以正确识别挂在根节点上的元素数量。尽管如此，它们都指的是第一个元素的属性......

我不是 C++ 方面的专家，而且对 Boost 来说真的很陌生，所以这可能是我在哈希映射处理方面所缺少的东西......任何建议都将不胜感激。

4

3 回答 3

19

您的程序的问题位于这一行：

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

使用这条线，您要求从那里得到孩子pet.<xmlattr>，pets并且您独立于f您正在遍历的任何一个进行此操作 3 次。在这篇文章之后，我猜你需要使用的是：

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

适用于您的两个 xml 文件的完整代码是：

#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;
        }
    }
}
于 2012-12-23T12:02:19.630 回答
2

到目前为止，如果没有使用过这个特性，我会怀疑boost::property_treeXML 解析器不是一个常见的 XML 解析器，而是需要一个特定的模式，其中一个特定属性只有一个特定标记。

如果您想使用超出boost::property_tree功能范围的 XML，您可能更喜欢使用提供解析任何 XML 模式的其他 XML 解析器。看看例如Xerces C++或Poco XML。

于 2012-12-23T11:49:44.243 回答
1

要解析的文件，pets.xml

<pets>
    <pet type="cat" name="Garfield" weight="4Kg">
        <something name="test" value="*"/>
         <something name="demo" value="@"/>
    </pet>
    <pet type="dog" name="Milu" weight="7Kg">
         <something name="test1" value="$"/>
    </pet>
    <birds type="parrot">
        <bird name="african grey parrot"/>
        <bird name="amazon parrot"/>
    </birds>
</pets>

代码：

// DemoPropertyTree.cpp : Defines the entry point for the console application.
//Prerequisite boost library

#include "stdafx.h"
#include <boost/property_tree/xml_parser.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/foreach.hpp>
#include<iostream>
using namespace std;
using namespace boost;
using namespace boost::property_tree;

void processPet(ptree subtree)
{
    BOOST_FOREACH(ptree::value_type petChild,subtree.get_child(""))
    {
        //processing attributes of element pet
        if(petChild.first=="<xmlattr>")
        {
            BOOST_FOREACH(ptree::value_type petAttr,petChild.second.get_child(""))
            {
                cout<<petAttr.first<<"="<<petAttr.second.data()<<endl;
            }
        }
        //processing child element of pet(something)
        else if(petChild.first=="something")
        {
            BOOST_FOREACH(ptree::value_type somethingChild,petChild.second.get_child(""))
            {
                //processing attributes of element something
                if(somethingChild.first=="<xmlattr>")
                {
                    BOOST_FOREACH(ptree::value_type somethingAttr,somethingChild.second.get_child(""))
                    {
                        cout<<somethingAttr.first<<"="<<somethingAttr.second.data()<<endl;
                    }
                }
            }
        }
    }
}
void processBirds(ptree subtree)
{
    BOOST_FOREACH(ptree::value_type birdsChild,subtree.get_child(""))
    {
        //processing attributes of element birds
        if(birdsChild.first=="<xmlattr>")
        {
            BOOST_FOREACH(ptree::value_type birdsAttr,birdsChild.second.get_child(""))
            {
                cout<<birdsAttr.first<<"="<<birdsAttr.second.data()<<endl;
            }
        }
        //processing child element of birds(bird)
        else if(birdsChild.first=="bird")
        {
            BOOST_FOREACH(ptree::value_type birdChild,birdsChild.second.get_child(""))
            {
                //processing attributes of element bird
                if(birdChild.first=="<xmlattr>")
                {
                    BOOST_FOREACH(ptree::value_type birdAttr,birdChild.second.get_child(""))
                    {
                        cout<<birdAttr.first<<"="<<birdAttr.second.data()<<endl;
                    }
                }
            }
        }
    }
}
int _tmain(int argc, _TCHAR* argv[])
{

    const std::string XML_PATH1 = "C:/Users/10871/Desktop/pets.xml";
    ptree pt1;
    boost::property_tree::read_xml( XML_PATH1, pt1  );
     cout<<"********************************************"<<endl;
    BOOST_FOREACH( ptree::value_type const& topNodeChild, pt1.get_child( "pets" ) ) 
    {
        ptree subtree = topNodeChild.second;
        if( topNodeChild.first == "pet" ) 
        {
             processPet(subtree);
             cout<<"********************************************"<<endl;
        }
        else if(topNodeChild.first=="birds")
        {
            processBirds(subtree);
             cout<<"********************************************"<<endl;
        }

    }
    getchar();
    return 0;
}

输出显示在这里： 输出

于 2019-05-16T03:36:20.390 回答