c++ - 使用结构的二维 vector

Question

所以我有以下代码，我在其中读取 XML 文件并将值保存到 vector 中。我对 vector 没有太多经验，但现在我有了参数“motor”，我希望能够获取电机值，并从该 vector 中读取参数。

我必须向我的结构添加一些东西吗？或者初始化一个二维 vector vector<vector <NameValue>> motors;如果我确实初始化了一个 2D vector ，我将如何填充该 vector 。或者有什么好的指南可以帮助我完全理解 vector ？

这是 TinyXML 的文档。 http://www.grinninglizard.com/tinyxmldocs/index.html

#include <QCoreApplication>
#include <iostream>
#include <string>
#include <vector>
#include <stdexcept>
#include <tinyxml.h>

using namespace std; 

struct NameValue
{
    string motor;
    string name;
    string value;
};

vector<NameValue> read()
{   //READING XML FILE
    QString directory;
    string file;
    directory = QCoreApplication::applicationDirPath();
    file = directory.toUtf8().constData();
    file = file + "/Profile.xml";
    cout<<file<<endl;
    TiXmlDocument doc (file);
    if(!doc.LoadFile()){
        cout<<"Cannot open file"<<endl;}

    vector<NameValue> xmlread;
    NameValue elem;

    TiXmlElement *pRoot, *pParm, *pMotor;
    pRoot = doc.FirstChildElement("PRO");
    if (pRoot) //parsing
    {
     pMotor = pRoot->FirstChildElement("Motor");
      if(pMotor){
        while (pMotor)
        {
            elem.motor = pMotor->Attribute("value");
            pParm = pMotor->FirstChildElement("PARAMETER");
            while (pParm)
            {
                elem.name = pParm->Attribute("name");
                elem.value = pParm->Attribute("value");
                xmlread.push_back(elem);
                pParm = pParm->NextSiblingElement("PARAMETER");
            }
            pMotor = pMotor->NextSiblingElement("Motor");

        }
   }
}
   return xmlread;
}
int main (int argc, char *argv[])
{
   vector<NameValue> elems = read();
   cout<<elems[0].motor<<endl;

}

这是我的 XML 文件的片段:

<PRO>
   <Motor value = "1">
         <PARAMETER name = "SPEED" value = "100" />
         <PARAMETER name = "LOOP" value = "1" />
         <PARAMETER name = "DEADBAND" value = "10" />
   </Motor>
   <Motor value = "2">
         <PARAMETER name = "SPEED" value = "100" />
         <PARAMETER name = "LOOP" value = "1" />
         <PARAMETER name = "DEADBAND" value = "10" />
   </Motor>
   <Motor value = "3">
         <PARAMETER name = "SPEED" value = "100" />
         <PARAMETER name = "LOOP" value = "1" />
         <PARAMETER name = "DEADBAND" value = "10" />
   </Motor>
</PRO>

Answer 1

为了生成 2D vector ，您已经拥有的东西需要很少的修改。只需使用 emplace_back就地构建内部 vector :

vector<vector<NameValue>> xmlread2D;
NameValue elem;

TiXmlElement *pRoot, *pParm, *pMotor;
pRoot = doc.FirstChildElement("PRO");
if (pRoot)
{
    pMotor = pRoot->FirstChildElement("Motor");
    while (pMotor)
    {
        // allocate new inner vector
        xmlread2D.emplace_back();
        auto& xmlread = xmlread2D.back();
        // in C++17 the above can be replaced with a single line

        // unmodified inner loop
        elem.motor = pMotor->Attribute("value");
        pParm = pMotor->FirstChildElement("PARAMETER");
        while (pParm)
        {
            elem.name = pParm->Attribute("name");
            elem.value = pParm->Attribute("value");
            xmlread.push_back(elem);
            pParm = pParm->NextSiblingElement("PARAMETER");
        }
        pMotor = pMotor->NextSiblingElement("Motor");
    }
}