包含目录：

#include <QJsonObject>
#include <QJsonDocument>
#include <QByteArray>
#include <QFile>
#include <QJsonArray>

基本结构：

写json

QJsonObject studentobj;
    QJsonArray arrarydata;
    QJsonObject subdata;
    int id = 01;
    QString name = "zhangsan";
    QString gender = "Male";
   subdata.insert("id", QJsonValue(id));
   subdata.insert("name", QJsonValue(name));
   subdata.insert("gender", QJsonValue(gender));
   arrarydata.append(QJsonValue(subdata));
   id = 02;
   name = "lisi";
   gender = "Male";
   subdata.insert("id", QJsonValue(id));
   subdata.insert("name", QJsonValue(name));
   subdata.insert("gender", QJsonValue(gender));
   arrarydata.append(QJsonValue(subdata));
   studentobj.insert("Student", QJsonValue(arrarydata));
    //写入到文件，名字为info.json
    QJsonDocument docs(studentobj);
    QByteArray datas = docs.toJson();
    QFile files("student.json");
    bool oks = files.open(QIODevice::WriteOnly);
    if (oks)
    {
         files.write(datas);
         files.close();
    }
    else
    {
         qDebug() << "write error!" << endl;
    }

读json

QFile file("student.json");
    file.open(QIODevice::ReadOnly);
    QByteArray data = file.readAll();
    file.close();
    //解析
    QJsonParseError parseError;
    QJsonDocument doc = QJsonDocument::fromJson(data, &parseError);
    if (parseError.error != QJsonParseError::NoError) {
        qDebug() << "error";
        return;
    }
    QJsonObject obj = doc.object();
    if (obj.contains("Student"))
    {
        QJsonValue arrayTemp = obj.value("Student");
        QJsonArray array = arrayTemp.toArray();
        qDebug() << "array size: " << array.size();// size: 2
        QJsonValue sub = array.at(0);//因为里面就一个元素，如果有多个元素，可以通过array.size()遍历
        QJsonObject subObj = sub.toObject();
        int  id = subObj.value("id").toInt();
        QString name = subObj.value("name").toString();
        QString gender = subObj.value("gender").toString();
    }

复合结构：

	QJsonArray ArrayALL;
    QJsonObject studentobj;
    QJsonArray studentarrarydata;
    QJsonObject studentsubdata;
    int id = 01;
    QString name = "zhangsan";
    QString gender = "Male";
    studentsubdata.insert("id", QJsonValue(id));
    studentsubdata.insert("name", QJsonValue(name));
    studentsubdata.insert("gender", QJsonValue(gender));
    studentarrarydata.append(QJsonValue(studentsubdata));
    id = 02;
    name = "lisi";
    gender = "Male";
   studentsubdata.insert("id", QJsonValue(id));
   studentsubdata.insert("name", QJsonValue(name));
   studentsubdata.insert("gender", QJsonValue(gender));
   studentarrarydata.append(QJsonValue(studentsubdata));
   studentobj.insert("Student", QJsonValue(studentarrarydata));
   QJsonObject scoreobj;
   QJsonArray scorearrarydata;
   QJsonObject scoresubdata;
   id = 01;
   double math = 95;
   double physics = 85;
   double english = 66;
   scoresubdata.insert("ID", id);
   scoresubdata.insert("Math", math);
   scoresubdata.insert("Physics", physics);
   scoresubdata.insert("English", english);
   scorearrarydata.append(scoresubdata);
   id = 02;
   math = 85;
   physics = 95;
   english = 86;
   scoresubdata.insert("ID", id);
   scoresubdata.insert("Math", math);
   scoresubdata.insert("Physics", physics);
   scoresubdata.insert("English", english);
   scorearrarydata.append(scoresubdata);
   scoreobj.insert("Score", scorearrarydata);
   ArrayALL.append(studentobj);
   ArrayALL.append(scoreobj);
   QJsonDocument jsonDoc;
   jsonDoc.setArray(ArrayALL);
   QByteArray json = jsonDoc.toJson();
   //写文件
   QFile file0("test.json");
   file0.open(QIODevice::WriteOnly);
   file0.write(json);
   file0.close();

读文件

QFile file("info.json");
file.open(QIODevice::ReadOnly);
QByteArray data = file.readAll();
file.close();
//解析
QJsonParseError parseError;
QJsonDocument document= QJsonDocument::fromJson(data, &parseError);
if (parseError.error != QJsonParseError::NoError) {
    qDebug() << "error";
    return;
}
if(document.isArray())
{
            int Num = document.array().size();
             for(int i = 0; i <  Num ; ++i)
            {
                QJsonObject obj = document[i].toObject();
                QJsonValue value = obj.value("Student");
                int size = value.toArray().size();  //size=2
                	for(int j = 0 ; j < size;++j)
                    {
                        QJsonObject objData = value[j].toObject();
                       	int  id = objData .value("id").toInt();
                        ........
                    }
			}
            ......   
}