c++ - 使用boost库更新具有相同名称的每个节点的XML属性值时出现的问题

Question

我正在尝试在找到的每个totalresult节点中更新test_list属性的值。问题是，它将仅更新找到的第一个test_list节点。
每次添加test_list节点时，testListCount都会增加。添加完test_list节点后，每个totalresult值将在每个test_list节点中更新。
这是我的代码:

BOOST_FOREACH(ptree::value_type const & subTree, mainTree.get_child("my_report"))
{
    auto &nodeTestList = mainTree.get_child("my_report.test_list");
    BOOST_FOREACH(ptree::value_type const & subval, nodeTestList)
    {
        ptree subvalTree = subval.second;
        BOOST_FOREACH(ptree::value_type const & paramNode, subvalTree)
        {
            std::string name = paramNode.first;
            if (name == TestListAttrib[TestListParam::TOTALRESULT])
            {
                wxMessageBox("firing!");
                nodeTestList.put("<xmlattr>." + name, testListCount);
            }
        }
    }
}

以下是实际结果:

<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type="text/xsl" href="report.xsl"?>
<my_report>
    <test_list overall_status="FAILED" result="1" totalresult="3">
    <test_list overall_status="FAILED" result="2" totalresult=""/>
    <test_list overall_status="FAILED" result="3" totalresult=""/>
</my_report>

以下是预期结果:

<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type="text/xsl" href="report.xsl"?>
<my_report>
    <test_list overall_status="FAILED" result="1" totalresult="3">
    <test_list overall_status="FAILED" result="2" totalresult="3"/>
    <test_list overall_status="FAILED" result="3" totalresult="3"/>
</my_report>

Answer 1

就像其他人说的那样，属性树不是XML库(请参阅What XML parser should I use in C++?)。
也就是说，您的错误似乎在这里:

for (auto const &subTree : mainTree.get_child("my_report")) {
    auto &nodeTestList = mainTree.get_child("my_report.test_list");

第二行根本不使用 subTree，而只匹配 "my_report.test_list"中的第一个 mainTree节点。
使用现代C++和编译器警告
我使代码自成一体的c++ 11:

#include <boost/property_tree/xml_parser.hpp>
using boost::property_tree::ptree;

enum TestListParam { OVERALLSTATUS, TOTALRESULT };
std::array<std::string, 2> TestListAttrib{ "overall_status", "totalresult" };

int main() {
    ptree mainTree;
    {
        std::ifstream ifs("input.xml");
        read_xml(ifs, mainTree);
    }

    auto const testListCount = 3;

    for (auto const& subTree : mainTree.get_child("my_report")) {
        auto& nodeTestList = mainTree.get_child("my_report.test_list");
        for (auto& subval : nodeTestList) {
            ptree subvalTree = subval.second;
            for (auto& paramNode : subvalTree) {
                std::string name = paramNode.first;
                if (name == TestListAttrib[TestListParam::TOTALRESULT]) {
                    nodeTestList.put("<xmlattr>." + name, testListCount);
                }
            }
        }
    }
}

如果启用编译器警告，则会看到错误:
Live On Wandbox

prog.cc:16:22: warning: unused variable 'subTree' [-Wunused-variable]
    for (auto const& subTree : mainTree.get_child("my_report")) {
                     ^
1 warning generated.

更现代的C++
利用C++ 17的优点，事情变得更清晰，更容易修复。这是第一张照片，还添加了输出打印:
Live On Wandbox

#include <boost/property_tree/xml_parser.hpp>
#include <iostream>
using boost::property_tree::ptree;
auto const pretty = boost::property_tree::xml_writer_make_settings<std::string>(' ', 4);

enum TestListParam { OVERALLSTATUS, TOTALRESULT };
std::array<std::string, 2> TestListAttrib{ "overall_status", "totalresult" };

int main() {
    ptree mainTree;
    {
        std::ifstream ifs("input.xml");
        read_xml(ifs, mainTree);
    }

    auto const testListCount = 3;

    for (auto& [key, subTree] : mainTree.get_child("my_report"))
    for (auto& [name, node] : subTree.get_child("<xmlattr>")) {
        if (name == TestListAttrib[TestListParam::TOTALRESULT]) {
            node.put_value(testListCount);
        }
    }

    write_xml(std::cout, mainTree, pretty);
}

打印:(减少空白)

<?xml version="1.0" encoding="utf-8"?>
<my_report>
    <test_list overall_status="FAILED" result="1" totalresult="3"/>
    <test_list overall_status="FAILED" result="2" totalresult="3"/>
    <test_list overall_status="FAILED" result="3" totalresult="3"/>
</my_report>

注意事项
注意由于我们编写循环代码的方式

如果找不到 <xmlattr>或 my_report，则

将失败

相反，即使名称与my_report不同，也会错误地降级test_list的所有子节点

XSL处理指令丢失。同样，这是固有的，因为Boost属性树不了解XML。它使用XML的子集来实现属性树的序列化。

为了解决前两个问题，我建议创建一个帮助程序来从XML(从 Iterating on xml file with boost)查询节点:

enumerate_nodes(mainTree,
        "my_report.test_list.<xmlattr>.totalresult", 
        back_inserter(nodes));

这不会遇到任何提到的问题，您可以优雅地配置所有匹配的节点:

for (ptree& node : nodes)
    node.put_value(3);

如果您确实不是/想要/要求 test_list节点名称，请使用通配符:

enumerate_nodes(mainTree,
        "my_report.*.<xmlattr>.totalresult", 
        back_inserter(nodes));

现场演示
Live On Wandbox

#include <boost/property_tree/xml_parser.hpp>
#include <iostream>
using boost::property_tree::ptree;
auto const pretty = boost::property_tree::xml_writer_make_settings<std::string>(' ', 4);

enum TestListParam { OVERALLSTATUS, TOTALRESULT };
std::array<std::string, 2> TestListAttrib{ "overall_status", "totalresult" };

template <typename Ptree, typename Out>
Out enumerate_nodes(Ptree& pt, ptree::path_type path, Out out) {
    if (path.empty())
        return out;

    if (path.single()) {
        auto name = path.reduce();
        for (auto& child : pt) {
            if (child.first == name)
                *out++ = child.second;
        }
    } else {
        auto head = path.reduce();
        for (auto& child : pt) {
            if (head == "*" || child.first == head) {
                out = enumerate_nodes(child.second, path, out);
            }
        }
    }

    return out;
}


int main() {
    ptree mainTree;
    {
        std::ifstream ifs("input.xml");
        read_xml(ifs, mainTree);
    }

    std::vector<std::reference_wrapper<ptree> > nodes;
    enumerate_nodes(mainTree,
            "my_report.test_list.<xmlattr>.totalresult", 
            back_inserter(nodes));

    for (ptree& node : nodes)
        node.put_value(3);

    write_xml(std::cout, mainTree, pretty);
}

版画

<?xml version="1.0" encoding="utf-8"?>
<my_report>
    <test_list overall_status="FAILED" result="1" totalresult="3"/>
    <test_list overall_status="FAILED" result="2" totalresult="3"/>
    <test_list overall_status="FAILED" result="3" totalresult="3"/>
</my_report>