Save/Read struct to/from File

droelf

I have to save multiple pairs of (QPointF, Int) in a file and need to read them again.

This is my idea right now:

 typedef pair<QPointF,int> vertex_info;   

 struct graph_info{
       QList<vertex_info> all_vertices;
 };


void MainWindow::on_button_save_clicked(){
   QString s = this->ui->lineEdit->text();
   this->ui->lineEdit->clear();

   struct graph_info my_graph;

   vmap::iterator itr = myLogic->set.begin();
   while(itr != myLogic->set.end()){
        v = itr->second;
       my_graph.all_vertices.append(vertex_info(v->pos,v->type));
    
       itr++;
    }

   QFile new_graph(s);
   new_graph.open(QIODevic::WriteOnly);

    
}

How to save/read my struct properly?

mcosta

Hi,

I suggest to create QDataStream::operator<<() and QDataStream::operator>>() for your structure

QDataStream& operator<<(QDataStream& stream, const graph_info& info) 
{
 ...
}

QDataStream& operator>>(QDataStream& stream, graph_info& info) 
{
 ...
}

In that case you can save your data

QFile file("file.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);   // we will serialize the data into the file
out << my_graph;

and read

QFile file("file.dat");
file.open(QIODevice::ReadOnly);
QDataStream in(&file);    // read the data serialized from the file
in >> my_graph;

UPDATE: a complete different approach is to save your data in text format (for example JSON). Here you'll find a great example

droelf

@mcosta

thx for the fast answer, but how does the inside of these QDataStream declarations look like?

And what happens exactly in line:

      in >> my_graph;

The Stream "in" looks into the file "file.dat" and reads it.

Sry i am kind of new but a task at my University forces me to find an answer to this problem :/

mcosta

Hi,

you have to implements the << and >> operators for your struct.
Read the QDataStream Documentation to understand how implement them

droelf

I came to this point:

struct vertex_info{
     QPointF pos;
     int type;
};


struct graph_info{
    QList<vertex_info> all_vertices;
 };


 QDataStream &operator<<(QDataStream &out, const vertex_info &v){

       out << v.pos << v.type;
      return out;
 }



 QDataStream &operator<<(QDataStream &out, const graph_info &g){

       int n = g.all_vertices.size();

       for(int i=0; i<n ;i++){
               out<<g.all_vertices.at(i);
        }

        return out;
  }







     QDataStream &operator>>(QDataStream &in, graph_info &g){
             QList<vertex_info> L;


             return in;
      }



      QDataStream &operator>>(QDataStream &in, vertex_info &v){



              return in;
       }



   void MainWindow::on_button_save_clicked(){
            QString s = this->ui->lineEdit->text();
            this->ui->lineEdit->clear();

            vmap::iterator itr = myLogic->set.begin();
            graph_info my_graph = new graph_info();


            vertex_info vinfo;

           while(itr != myLogic->set.end()){
                   vinfo.first = itr->second->pos;
                   vinfo.second = itr->second->type;
                   my_graph.all_vertices.append(vinfo);
                   itr++;
            }


           QFile file(s);
           file.open(QIODevice::WriteOnly);
           QDataStream stream(&file);
           stream << my_graph;

           file.close();
        }

Any suggestions or solutions? :/

droelf

Anyone? :/

mcosta

Hi,

you have to decide the format of your file; we got you information how to use properly the QT classes but you should thing about the format.