Boost属性树add_child指定路径

boost property tree add_child specifying the path

本文关键字：路径 child 属性 add Boost      更新时间：2023-10-16

我使用boost::property_tree来操作一些XML。我必须在xml文档中添加子节点

xml文档看起来像这样:

<MPD>
    <Period>
        <AdaptationSet mimeType="audio/mp4" segmentAlignment="true" startWithSAP="1">
            <ContentProtection schemeIdUri="urn:mpeg:dash:mp4protection:2011" value="cenc"/>
            <ContentProtection schemeIdUri="urn:uuid:9a04f079-9840-4286-ab92-e65be0885f95">
                <!-- value already exists here //-->
                <!-- need to insert new entry here //-->
            </ContentProtection>
        </AdaptationSet>
        <AdaptationSet>
            <ContentProtection ... />
            <ContentProtection ... />
            <ContentProtection ... />
        </AdaptationSet>
    </Period>
</MPD>
因此，我使用以下代码将新条目插入到上面XML中标记的位置: 
typedef boost::property_tree::iptree        property_tree_t;
typedef boost::shared_ptr<property_tree_t>  shared_ptree_t;
typedef boost::optional<property_tree_t &>  optional_ptree_t;
string sSearchSchemeIdUri = "urn:uuid:9a04f079-9840-4286-ab92-e65be0885f95";
string sChildName;
optional_ptree_t spPeriod = spPTree->get_child_optional("MPD.Period");
if (spPeriod)
{
    for (auto & adaptSetNextChild : spPeriod->get_child("AdaptationSet"))
    {
        sChildName = adaptSetNextChild.first;
        if (sChildName.compare("ContentProtection") == 0)
        {
            property_tree_t &   ptContentProtection = adaptSetNextChild.second;
            string              sSchemeIdUri        = ptContentProtection.get<string>("<xmlattr>.schemeIdUri", "");
            if (sSchemeIdUri.compare(sSearchSchemeIdUri) == 0)
            {
                property_tree_t ptPssh;
                ptPssh.clear();
                ptPssh.add("cenc:PSSH", sPssh);
                ptContentProtection.add_child("./", ptPssh);
            }
        }
    }
}

上面的代码将添加的数据包装在下面:

<></>
<//></>

我想避免。

这个错误的标记来自我的add_child调用，它将插入路径指定为"./"

不指定会导致异常，这是我发现的唯一有效的方法。

读取了ptree.hpp的头文件，其中声明参数为

/** Add the node at the given path. Create any missing parents. If there
* already is a node at the path, add another one with the same key.
* @param path Path to the child. The last fragment must not have an
*             index.
* @return A reference to the inserted subtree.
* @note Because of the way paths work, it is not generally guaranteed
*       that a node newly created can be accessed using the same path.
*/
self_type &add_child(const path_type &path, const self_type &value);

是否有任何方法可以指定当前路径，例如:ptContentProtection的路径?

您可能希望使用put成员而不是add成员。

下面是用NEW VALUE代替OLD VALUE的示例:

Live On Coliru 

#include <boost/property_tree/xml_parser.hpp>
#include <iostream>
static std::string const sample = R"(<MPD>
    <Period>
        <AdaptationSet mimeType="audio/mp4" segmentAlignment="true" startWithSAP="1">
            <ContentProtection schemeIdUri="urn:mpeg:dash:mp4protection:2011" value="cenc"/>
            <ContentProtection schemeIdUri="urn:uuid:9a04f079-9840-4286-ab92-e65be0885f95">OLD VALUE</ContentProtection>
        </AdaptationSet>
        <AdaptationSet>
        </AdaptationSet>
    </Period>
</MPD>)";
static std::string sSearchSchemeIdUri = "urn:uuid:9a04f079-9840-4286-ab92-e65be0885f95";
int main() {
    using boost::property_tree::iptree;
    iptree pt;
    {
        std::istringstream iss(sample);
        read_xml(iss, pt);
    }
    for (auto& as : pt.get_child("MPD.Period")) {
        if (as.first == "AdaptationSet") {
            for (auto& cp : as.second) {
                if (cp.first == "ContentProtection" && cp.second.get("<xmlattr>.schemeIdUri", "") == sSearchSchemeIdUri)
                {
                    cp.second.put_value("NEW VALUE");
                }
            }
        }
    }
    auto xws = boost::property_tree::xml_writer_make_settings<std::string>(' ', 4);
    write_xml(std::cout, pt, xws);
}
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