[提问]怎么引用变量的值不能改变原本的值? [复制链接]

我重载>>操作符,可是不能改变原来的值的?
QDataStream &operator >>(QDataStream &in,Painting &painting)
{
    int year;
    QString title,artist;
    in>>artist>>year>>title;
    painting = Painting(title,artist,year);
调试发现这里是改变了,可是在主函数那里的输出还是没改变...
    return in;
}