rapidxml – 覆盖以前的xml_nodes

这是我手动创作的.

<?xml version="1.0" encoding="utf-8"?>
<GPS>
    <Path>    
        <Point X="-3684.136" Y="3566.282" Z="285.2893" />
        <Point X="-3681.816" Y="3540.431" Z="283.3658" />
        <Point X="-3687.079" Y="3515.315" Z="282.6284" />
    </Path>
</GPS>

我可以轻松阅读,没有任何问题.然后我想把它写到一个新文件.
但问题是它不断覆盖以前的xml_nodes.

例如,

<?xml version="1.0" encoding="UTF-8"?>
<GPS>
    <Path>
        <Point X="-3687.08" Y="3515.31" Z="282.628"/>
        <Point X="-3687.08" Y="3515.31" Z="282.628"/>
        <Point X="-3687.08" Y="3515.31" Z="282.628"/>
    </Path>
</GPS>

这是创建该xml文件的代码,

int Write(pathStruct *toStore)
{
    xml_document<> doc;

    xml_node<>* decl = doc.allocate_node(node_declaration);
    decl->append_attribute(doc.allocate_attribute("version","1.0"));
    decl->append_attribute(doc.allocate_attribute("encoding","UTF-8"));
    doc.append_node(decl);  

    xml_node<> *GPS = doc.allocate_node(node_element,"GPS");
    doc.append_node(GPS);

    cout << "Saving GrindPath " << endl;
    xml_node<> *Path = doc.allocate_node(node_element,"Path");
    GPS->append_node(Path);

    for(int i = 0;i<3;i++) //Temp Static
    {
        xml_node<> *Point = doc.allocate_node(node_element,"Point");
        Path->append_node(Point);

        char x[10];
        FloatToCharA(toStore->X[i],x);
        Point->append_attribute(doc.allocate_attribute("X",x));

        char y[10];
        FloatToCharA(toStore->Y[i],y);
        Point->append_attribute(doc.allocate_attribute("Y",y));

        char z[10];
        FloatToCharA(toStore->Z[i],z);
        Point->append_attribute(doc.allocate_attribute("Z",z));

        //GrindPath->append_node(Point);
        //doc.first_node()->append_node(GrindPath);
        //Point = GrindPath->next_sibling();

        cout << "x:" << toStore->X[i] << "    y:" << toStore->Y[i] << "   z:" << toStore->Z[i] << endl;
    }

    cout << "Done! " << endl;
    std::ofstream myfile;
    myfile.open ("./toStore.xml");
    myfile << doc;
    return 0;

};

我的问题是他如何阻止它覆盖以前的xml_nodes？
我尝试过很多东西,但每次都会覆盖以前的xml_nodes.
我知道这一定很简单,或者我错过了大局.

谢谢你的帮助和时间！