使用libxml2解析XML文件时缺少元素值

static 局部变量很可能会中断处理。还记得吗 局部变量在函数调用之间保持其值。一次 streamFile() 退出,然后再次调用 静止的 变量仍将保留其以前的值,不会重置回其原始值。你必须把他们改成你组织的成员 CXMLManager 流文件() 每次调用时都可以重置它们。

我不建议使用一个函数来处理您需要解析的每个可能的节点。我将把reading分解为不同的函数,这些函数在XML文档的每个级别上都有自己的职责,如下所示:

void CXMLManager::readFeed(xmlTextReaderPtr reader)
{
    // read attributes if needed...

    if (xmlTextReaderIsEmptyElement(reader))
        return;

    int depth = xmlTextReaderNodeDepth(reader);
    int ret;

    while ((ret = xmlTextReaderRead(reader)) == 1)
    {
        switch (xmlTextReaderNodeType(reader))
        {
            case XML_READER_TYPE_ELEMENT:
            {
                if (xmlStrEqual(xmlTextReaderConstLocalName(reader), BAD_CAST "entry"))
                {
                    CFeed entry;
                    readFeedEntry(reader, entry);
                    m_feedBuffer.push_back(entry);
                }
                break;
            }

            case XML_READER_TYPE_END_ELEMENT:
            {
                if ((xmlTextReaderNodeDepth(reader) == depth)
                    /*&& xmlStrEqual(xmlTextReaderConstLocalName(reader), BAD_CAST "feed")*/)
                {
                    return;
                }
                break;
            }
        }
    }

    if (ret == -1)
        throw CFeedreaderException("FEEDREADER: Failed to read XML.", ...);
}

void CXMLManager::readFeedEntry(xmlTextReaderPtr reader, CFeed &entry)
{
    // read attributes if needed...

    if (xmlTextReaderIsEmptyElement(reader))
        return;

    int depth = xmlTextReaderNodeDepth(reader);
    int ret;

    while ((ret = xmlTextReaderRead(reader)) == 1)
    {
        switch (xmlTextReaderNodeType(reader))
        {
            case XML_READER_TYPE_ELEMENT:
            {
                const xmlChar *name = xmlTextReaderConstLocalName(reader);

                if (xmlStrEqual(name, BAD_CAST "title"))
                {
                    readText(reader, entry.m_title/*, BAD_CAST "title"*/);
                    std::cout << "Title: " << entry.m_title << std::endl;
                }
                // else other <entry> children as needed ...

                break;
            }

            case XML_READER_TYPE_END_ELEMENT:
            {
                if ((xmlTextReaderNodeDepth(reader) == depth)
                    /*&& xmlStrEqual(xmlTextReaderConstLocalName(reader), BAD_CAST "entry")*/)
                {
                    return;
                }
                break;
            }
        }
    }

    if (ret == -1)
        throw CFeedreaderException("FEEDREADER: Failed to read XML.", ...);
}

void CXMLManager::readText(xmlTextReaderPtr reader, std::string &text/*, const xmlChar *tagName */)
{
    text.clear();

    if (xmlTextReaderIsEmptyElement(reader))
        return;

    int depth = xmlTextReaderNodeDepth(reader);
    int ret;

    while ((ret = xmlTextReaderRead(reader)) == 1)
    {
        switch (xmlTextReaderNodeType(reader))
        {
            // TODO: handle XML_READER_TYPE_ELEMENT if you need to treat
            // embedded XML elements as part of the text, such as for
            // formatting instructions (like <b>, <i>, etc)...

            case XML_READER_TYPE_TEXT:
            {
                const xmlChar *value = xmlTextReaderConstValue(reader);
                text += reinterpret_cast<const char*>(value);
                break;
            }

            case XML_READER_TYPE_END_ELEMENT:
            {
                if ((xmlTextReaderNodeDepth(reader) == depth)
                    /*&& xmlStrEqual(name, tagName)*/)
                {
                    return;
                }
                break;
            }
        }
    }

    if (ret == -1)
        throw CFeedreaderException("FEEDREADER: Failed to read XML.", ...);
}

void CXMLManager::streamFile(const char *data, size_t size)
{
    /*
     * Pass some special parsing options to activate DTD attribute defaulting,
     * entities substitution and DTD validation
     */
    xmlTextReaderPtr reader = xmlReaderForMemory(data, size, NULL, NULL,
                XML_PARSE_DTDATTR |  /* default DTD attributes */
                XML_PARSE_NOENT);    /* substitute entities */

    if (!reader)
        throw CFeedreaderException("FEEDREADER: Failed to parse XML.", E_WRONG_XML);

    std::unique_ptr<xmlTextReader, decltype(xmlFreeTextReader)> reader_deleter(reader, xmlFreeTextReader);
    int ret;

    while ((ret = xmlTextReaderRead(reader)) == 1)
    {
        if ((xmlTextReaderNodeType(reader) == XML_READER_TYPE_ELEMENT)
            && xmlStrEqual(xmlTextReaderConstLocalName(reader), BAD_CAST "feed"))
        {
            readFeed(reader);
        }
    }

    if (ret == -1)
        throw CFeedreaderException("FEEDREADER: Failed to read XML.", ...);
}

或者,我建议完全去掉所有的helper函数,只在 流文件() 它本身,使用本地状态机在 reader 例如:

void CXMLManager::streamFile(const char *data, size_t size)
{
    /*
     * Pass some special parsing options to activate DTD attribute defaulting,
     * entities substitution and DTD validation
     */
    xmlTextReaderPtr reader = xmlReaderForMemory(data, size, NULL, NULL,
                XML_PARSE_DTDATTR |  /* default DTD attributes */
                XML_PARSE_NOENT);    /* substitute entities */

    if (!reader)
        throw CFeedreaderException("FEEDREADER: Failed to parse XML.", E_WRONG_XML);

    std::unique_ptr<xmlTextReader, decltype(xmlFreeTextReader)> reader_deleter(reader, xmlFreeTextReader);

    std::string name, title, updated, author, link, text;
    int feedDepth = -1;
    int entryDepth = -1;
    int textDepth = -1;
    int ret;

    while ((ret = xmlTextReaderRead(reader)) == 1)
    {
        switch (xmlTextReaderNodeType(reader))
        {
            case XML_READER_TYPE_ELEMENT:
            {
                if (textDepth != -1)
                {
                    // TODO: handle this case if you need to treat embedded
                    // XML elements as part of the text, such as for formatting
                    // instructions (like <b>, <i>, etc)...
                    break;
                }

                const xmlChar *name = xmlTextReaderConstLocalName(reader);

                if (feedDepth == -1)
                {
                    if (xmlStrEqual(name, BAD_CAST "feed"))
                    {
                        // read attributes if needed...

                        feedDepth == xmlTextReaderNodeDepth(reader);
                    }
                }
                else if (entryDepth == -1)
                {
                    if (xmlStrEqual(name, BAD_CAST "entry"))
                    {
                        name = title = updated = author = link = text = "";

                        // read attributes if needed...

                        if (xmlTextReaderIsEmptyElement(reader))
                            m_feedBuffer.push_back( CFeed { name, title, updated, author, link } );
                        else
                            entryDepth == xmlTextReaderNodeDepth(reader);
                    }
                }
                else if (xmlStrEqual(name, BAD_CAST "title"))
                {
                    text.clear();
                    if (!xmlTextReaderIsEmptyElement(reader))
                        textDepth = xmlTextReaderNodeDepth(reader);
                    else
                        textDepth = -1;
                }
                // else other <entry> children as needed ...

                break;
            }

            case XML_READER_TYPE_TEXT:
            {
                if (textDepth != -1)
                {
                    const xmlChar *value = xmlTextReeaderConstValue(reader);
                    text += reinterpret_cast<const char*>(value);
                }

                break;
            }

            case XML_READER_TYPE_END_ELEMENT:
            {
                const xmlChar *name = xmlTextReaderConstLocalName(reader);

                if (textDepth != -1)
                {
                    if ((xmlTextReaderNodeDepth(reader) == textDepth)
                        /*&& xmlStrEqual(name, BAD_CAST "title")*/)
                    {
                        textDepth = -1;

                        title = text;
                        text.clear();

                        std::cout << "Title: " << title << std::endl;
                    }
                    // else other <entry> children as needed ...
                }
                else if (entryDepth != -1)
                {
                    if ((xmlTextReaderNodeDepth(reader) == entryDepth)
                        /*&& xmlStrEqual(name, BAD_CAST "entry")*/)
                    {
                        entryDepth = -1;
                        m_feedBuffer.push_back( CFeed { name, title, updated, author, link } );
                    }
                }
                else if (feedDepth != -1)
                {
                    if ((xmlTextReaderNodeDepth(reader) == feedDepth)
                        /*&& xmlStrEqual(name, BAD_CAST "feed")*/)
                    {
                        feedDepth = -1;
                    }
                }

                break;
            }
        }
    }

    if (ret == -1)
        throw CFeedreaderException("FEEDREADER: Failed to read XML.", ...);
}