Reading a XML file in C++ with TinyXML2

I'm pretty new to using XML in C++ and i'm trying to parse a list of files to download. THe XML file I'm using is generated via PHP and looks like this :

<?xml version="1.0"?>
<FileList>
  <File Name="xxx" Path="xxx" MD5="xxx" SHA1="xxx"/>
</FileList>

The code I'm using in C++ is the following, which I came up using some online tutorials (it's included in some global function):

tinyxml2::XMLDocument doc;

doc.LoadFile("file_listing.xml");
tinyxml2::XMLNode* pRoot = doc.FirstChild();
tinyxml2::XMLElement* pElement = pRoot->FirstChildElement("FileList");
if (pRoot == nullptr)
{
    QString text = QString::fromLocal8Bit("Error text in french");
    //other stuff
}
else
{
    tinyxml2::XMLElement* pListElement = pElement->FirstChildElement("File");
    while (pListElement != nullptr)
    {
        QString pathAttr = QString::fromStdString(pListElement->Attribute("Path"));
        QString md5Attr = QString:: fromStdString(pListElement->Attribute("MD5"));
        QString sha1Attr = QString::fromStdString(pListElement->Attribute("SHA1"));

        QString currentPath = pathAttr.remove("path");
        QString currentMd5 = this->fileChecksum(currentPath, QCryptographicHash::Md5);
        QString currentSha1 = this->fileChecksum(currentPath, QCryptographicHash::Sha1);

        QFile currentFile(currentPath);

        if (md5Attr != currentMd5 || sha1Attr != currentSha1 || !currentFile.exists())
        {
            QString url = "url" + currentPath;
            this->downloadFile(url);
        }

        pListElement = pListElement->NextSiblingElement("File");
    }

Problem is, I get an error like "Access violation, this was nullptr" on the following line :

tinyxml2::XMLElement* pListElement = pElement->FirstChildElement("File");

Since I'm far from a pro when it comes to coding and I already searched the internet up and down, I hope that someone here can provide me some pointers.

Have a good day, folks.

I don't know if you have C++17 available, but you can remove a lot of noise by using auto* and if-init-expressions (or rely on the fact that pointers can be implicitly converted to boolean values.)

The main issue with your code is you were not using XMLElement* but instead a XMLNode. The function tinyxml2::XMLDocument::RootElement() automatically gets the top-most element for you.

Because you have an xml declaration at the top, FirstChild returns that...which doesn't have any children, so the rest of the code fails.

By using RootElement tinyxml knows to skip any leading non-element nodes (comments, doctypes, etc.) and give you <FileList> instead.

    tinyxml2::XMLDocument doc;
    auto err = doc.LoadFile("file_listing.xml");
    if(err != tinyxml2::XML_SUCCESS) {
        //Could not load file. Handle appropriately.
    } else {
        if(auto* pRoot = doc.RootElement(); pRoot == nullptr) {
            QString text = QString::fromLocal8Bit("Error text in french");
            //other stuff
        } else {
            for(auto* pListElement = pRoot->FirstChildElement("File");
                pListElement != nullptr;
                pListElement = pListElement->NextSiblingElement("File"))
            {
                QString pathAttr = QString::fromStdString(pListElement->Attribute("Path"));
                QString md5Attr = QString:: fromStdString(pListElement->Attribute("MD5"));
                QString sha1Attr = QString::fromStdString(pListElement->Attribute("SHA1"));

                QString currentPath = pathAttr.remove("path");
                QString currentMd5 = this->fileChecksum(currentPath, QCryptographicHash::Md5);
                QString currentSha1 = this->fileChecksum(currentPath, QCryptographicHash::Sha1);

                QFile currentFile(currentPath);
                if(md5Attr != currentMd5 || sha1Attr != currentSha1 || !currentFile.exists()) {
                    QString url = "url" + currentPath;
                    this->downloadFile(url);
                }
            }
        }
    }