Question

I am trying to retrieve some data from a binary file to put them in a linked list, here’s my code to write to the file:

void Pila::memorizzafile()
{
     int contatore = 0; 
     puntarec temp = puntatesta;
     ofstream miofile;
     miofile.open("data.dat" , ios::binary | ios::out);
     if(!miofile) cerr << "errore";
     else
     {
                while(temp)
                {
                            temp->elem.writes(miofile);
                            contatore++;
                            temp = temp->next;
                }
                //I go back at the beginning of the file to write how many elements I have
                miofile.seekp(0, ios::beg);
                miofile.write((const char *)&contatore , sizeof(int));
                miofile.close();
     }
}

And the function writes:

void Fiche::writes(ofstream &miofile)
{
     //Valore.
     miofile.write((const char *)&Valore,sizeof(int));
     //Materiale, I write the dimension of the string.
     int buff = strlen(Materiale);
     miofile.write((const char *)&buff,sizeof(int));
     //Writing the string
     miofile.write(Materiale,buff*sizeof(char));
     //Dimension of Forma
     buff = strlen(Forma);
     miofile.write((const char*)&buff,sizeof(int));
     //The string itself
     miofile.write(Forma,buff*sizeof(char));
     //Dimension of Colore.
     buff = strlen(Colore);
     miofile.write((const char*)&buff,sizeof(int));
     //The string
     miofile.write(Colore,buff*sizeof(char));
}

Now for the reading part, I am trying to make a constructor which should be able to read directly from the file, here it is:

Pila::Pila(char * nomefile)
{
     puntatesta = 0;
     int contatore = 0;
     ifstream miofile;
     miofile.open(nomefile  , ios::binary | ios::in);
     if(!miofile) cerr << "errore";
     else
     {
         //I read how many records are stored in the file
         miofile.read((char*)&contatore,sizeof(int));
         Fish temp;
         for(int i = 0; i < contatore; i++)
         {
                 temp.reads(miofile);
                 push(temp);
         }            
         miofile.close();
     }
}

And the reading function:

void Fiche::reads(ifstream &miofile)
{
     //I read the Valore
     miofile.read((char*)&Valore,sizeof(int));
     //I create a temporary char *

     char * buffer;
     int dim = 0;
     //I read how long will be the string
     miofile.read((char*)&dim,sizeof(int));
     buffer = new char[dim];
     miofile.read(buffer,dim);
     //I use the set function I created to copy the buffer to the actual member char*
     setMateriale(buffer);
     delete [] buffer;
     //Now it pretty much repeats itself for the other stuff
     miofile.read((char*)&dim,sizeof(int));
     buffer = new char[dim];
     miofile.read(buffer,dim);
     setForma(buffer);
     delete [] buffer;
     //And again.
     miofile.read((char*)&dim,sizeof(int));
     buffer = new char[dim];
     miofile.read(buffer,dim);
     setColore(buffer);
     delete [] buffer;    
}

The code doesn’t give me any error, but on the screen I read random characters and not even remotely close to what I wrote on my file. Anyone could help me out, please?

EDIT:

As requested here’s an example of input&output:

Fiche A("boh" , 4 , "no" , "gaia");
Fiche B("Marasco" , 3 , "boh" , "nonnt");
Fiche C("Valori" , 6 , "asd" , "hey");
Fiche D("TipO" , 7 , "lol" , "nonloso");
Pila pila;
pila.push(A);
pila.push(B);
pila.push(C);
pila.push(D);
pila.stampa();
pila.memorizzafile();

And:

Pila pila("data.dat");
pila.stampa();

Answer 1

This is probably your error:

            //I go back at the beginning of the file to write how many elements I have
            miofile.seekp(0, ios::beg);
            miofile.write((const char *)&contatore , sizeof(int));
            miofile.close();

By seeking to the beginning and then writing. You are overwriting part of the first object.

I think your best bet is to run through the list and count the elements first. Write this then proceed to write all the elements. It will probably be faster anyway (but you can time it to make sure).

I think you are using way to many C structures to hold things.

Also I would advice against a binary format unless you are saving huge amounts of information. A text format (for your data) is probably going to be just as good and will be human readable so you can look at the file and see what is wrong.