如何在Qt中使用数据库Sqlite保存和提取图片

#include "mainwindow.h"
//源码来自
//How to Store and Retrieve Image on SQLite
//https://wiki.qt.io/How_to_Store_and_Retrieve_Image_on_SQLite
#include <QApplication>
#include <QtSql>
#include <QtWidgets>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    // Set up database
    QString dbName("myDatabase.db3"); //默认路径在文件夹build-sqldemo-Desktop_Qt_5_12_9_MSVC2017_64bit-Debug
    QFile::remove(dbName);            // delete sqlite file if it exists from a previous run
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName(dbName);
    db.open();
    QSqlQuery query = QSqlQuery(db);
    query.exec("CREATE TABLE IF NOT EXISTS imgTable ( filename TEXT, imagedata BLOB )");
    // Generate an image (in this case a screenshot) and store it in a QByteArray
    QScreen *screen = a.primaryScreen();
    QPixmap inPixmap = screen->grabWindow(0);
    QByteArray inByteArray;
    QBuffer inBuffer(&inByteArray);
    inBuffer.open(QIODevice::WriteOnly);
    inPixmap.save(&inBuffer, "PNG"); // write inPixmap into inByteArray in PNG format
    // Alternatively, load an image file directly into a QByteArray
    // QFile file("screenshot.png");
    // if (!file.open(QIODevice::ReadOnly)) return;
    // QByteArray inByteArray = file.readAll();
    // Insert image bytes into the database
    // Note: make sure to wrap the :placeholder in parenthesis
    query.prepare("INSERT INTO imgTable (filename, imagedata) VALUES ('screenshot.png', :imageData)");
    query.bindValue(":imageData", inByteArray);
    if (!query.exec())
        qDebug() << "Error inserting image into table:\n"
                 << query.lastError();
    // Get image data back from database
    if (!query.exec("SELECT imagedata from imgTable"))
        qDebug() << "Error getting image from table:\n"
                 << query.lastError();
    query.first();
    QByteArray outByteArray = query.value(0).toByteArray();
    QPixmap outPixmap = QPixmap();
    outPixmap.loadFromData(outByteArray);
    db.close();
    // Display image
    QLabel myLabel;
    myLabel.setPixmap(outPixmap);
    myLabel.show();
    //MainWindow w;
    //w.show();
    return a.exec();
}

QFile file(fileName);
    if (!file.open(QIODevice::ReadOnly)) return;
    QByteArray byteArray = file.readAll();
    QSqlQuery query;
    query.prepare("INSERT INTO imgtable (imgdata) VALUES (?)");
    query.addBindValue(byteArray);
    query.exec();

QString connName = "basedb"
 QSqlDatabase db ;
 if(QSqlDatabase::contains(connName)){
        //如已经打开这个数据库，直接调出这个数据连接
      db = QSqlDatabase::database(connName);
    }else //否则打开这个数据库，注意带上数据库名
      db = QSqlDatabase::addDatabase("QSQLITE",connName);
//操作数据库1
QSqlQuery query;
//默认数据库1
query.exec("select * from student");
//操作数据库2
QSqlDatabase db2 = QSqlDatabase::addDatabase("QSQLITE","a");
//连接数据库2
QSqlQuery query(db2);
//绑定db2
query.exec("select * from teacher");