Qt使用Json-编程知识

Qt使用Json

包含目录：

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

基本结构：
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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.jsonQJsonDocument 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: 2QJsonValue 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();}

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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();

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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=2for(int j = 0 ; j < size;++j){QJsonObject objData = value[j].toObject();int  id = objData .value("id").toInt();........}}......   
}