Re: [suse-programming-e] (C++) Saving / reading structures to / from disk (desperate measures)

7 Jan 2004

      Hi

The writing to the file is working, but the load is still need to be 
done. If I will have the necessary time to do it I will, but that is not 
a promise :)
Maybe this helps you ...

Zsolt

#include <iostream>
#include <fstream>
#include <string.h>

using namespace std;

struct StockItem
{
   int code;
   char desc[20];
   float price;
}
stock[125];

/*struct bill_line
{
    StockItem product;
    float weight;
    float cost;
};

struct bill
{
    bill_line items[20];
    int num_lines;
};*/

void disp_menu(void);
struct StockItem enter_data();
void see_stock(StockItem stock[125], int num_items);
void save_data(StockItem * tosave, int size);
StockItem *load_data(StockItem toload[]);

int main()
{
   //StockItem stock[125];
   int ans;
   int num_items = 0;

   do
   {
      do
      {
         disp_menu();
         cin >> ans;
      } while((ans < 1) || (ans > 6));

      switch (ans)
      {
      case 1:
         stock[num_items] = enter_data();
         num_items++;
         break;
      case 2:
         see_stock(stock, num_items);
         break;
      case 3:
         save_data(stock, num_items);
         break;
      case 4:
      {
         //StockItem temp[125];
         StockItem *eerrmm = load_data(stock);
         break;
      }
      default:
         break;
      }
   } while(ans != 5);

   return 0;
}

void disp_menu()
{
   cout << "\n*** The Corner Shop ***\n\n";
   cout << "Select an option: \n\n";
   cout << "\t1. Enter new stock " << endl;
   cout << "\t2. See current stock " << endl;
   cout << "\t3. Save stock to disk " << endl;
   cout << "\t4. Load stock from disk " << endl;
   cout << "\t5. Exit \n" << endl;
   cout << "option> ";
}

StockItem enter_data()
{
   StockItem stock_item;

   memset(stock_item.desc, 0, sizeof(stock_item.desc));

   cout << "\n\nWhat is the product code: ";
   cin >> stock_item.code;
   cout << "What is the product description: ";
   cin.ignore();
   cin.getline(stock_item.desc, 20);
   cout << "What is the product price: ";
   cin >> stock_item.price;

   return (stock_item);
}

void see_stock(StockItem stock[125], int num_items)
{
   int ctr;
   char ret;

   cout << "\n\nHere is the stock listing:\n\n";
   for(ctr = 0; ctr < num_items; ++ctr)
   {
      cout << "Item " << ctr + 1 << endl;
      cout << "Product Code: " << stock[ctr].code << endl;
      cout << "Product Description: " << stock[ctr].desc << endl;
      cout << "Price: " << stock[ctr].price << endl;
      cout << "------------------------------------------------\n";
   }
   cout << "Press any key to return to the menu";
   if(cin >> ret)
      return;
}

//Problem sections
void save_data(StockItem* tosave, int size)
{
   ofstream fout("items.txt", ios::binary);
   if(!fout)
   {
      cout << "\n*** Error opening file ***\n";
   }

   for(int i = 0; i < size; i++){
       fout<<tosave->code<<":"<<tosave->desc<<":"<<tosave->price<<":";
       tosave++;
   }
   fout.close();
}

StockItem *load_data(StockItem * toload)
{
   ifstream fin("items.txt", ios::binary);
   if(!fin)
   {
      cout << "\n*** Error opening file ***\n";
   }
   fin.read((char *) &toload, sizeof(toload));
   fin.close();
   cout << toload;
   return toload;
}

ged.suse@ntlworld.com wrote:
...
Thanks to all who have helped so far :)
I don't have much time left to get this program running, so I have opted to drop the functions and try and get it running in the main().....
....however, I still can't get it to do what I want.
Can anyone PLEASE help me with this. I would be very grateful, I need to get this program running.
Cade now as follows:
#include <iostream>
#include <fstream>
using namespace std;
struct StockItem
{
   int code;
   char desc[20];
   float price;
}stock[125];
/*struct bill_line
{
   StockItem product;
   float weight;
   float cost;
};
struct bill
{
   bill_line items[20];
   int num_lines;
};*/
void disp_menu(void);
struct StockItem enter_data();
void see_stock(StockItem stock[125], int num_items);
main()
{
   int ans, ctr;
   int num_items = 0;
   FILE *item_file = NULL;
do
   {
       do
       {
           disp_menu();
           cin >> ans;
       } while ((ans<1) || (ans>6));
switch (ans)
       {
           case 1: 
               stock[num_items] = enter_data();
               num_items++;
               break; 
           case 2: 
               see_stock(stock, num_items);
               break;
           case 3: {
               item_file = fopen("items.txt", "ab");
               for (ctr=0;ctr<125;++ctr)
               {
                   fwrite(&stock[ctr], sizeof(StockItem), 3, item_file);
               }
               fclose(item_file);
               break; }
           case 4: {
               item_file = fopen("items.txt", "rb");
               for (ctr=0;ctr<125;++ctr)
               {
                   fread(&stock[ctr], sizeof(StockItem), 3, item_file);
               }
               fclose(item_file);                                   
               break; }
           default:
               break;
       } 
   }while (ans!=5);
return 0;
system("PAUSE");
   return 0;
}
void disp_menu()
{
   cout << "\n*** The Corner Shop ***\n\n";
   cout << "Select an option: \n\n";
   cout << "\t1. Enter new stock " << endl;
   cout << "\t2. See current stock " << endl;
   cout << "\t3. Save stock to disk " << endl;
   cout << "\t4. Load stock from disk " << endl;
   cout << "\t5. Exit \n" << endl;
   cout << "option> ";
}
StockItem enter_data()
{
   StockItem stock_item;
cout << "\n\nWhat is the product code: ";
   cin >> stock_item.code;
   cout << "What is the product description: ";
   fflush(stdin);
   cin.getline(stock_item.desc, 20);
   cout << "What is the product price: ";
   cin >> stock_item.price;
return (stock_item);
}
void see_stock(StockItem stock[125], int num_items)
{
   int ctr;
   char ret;
cout << "\n\nHere is the stock listing:\n\n";
   for (ctr = 0; ctr < num_items; ++ctr)
   {
       cout << "Item " << ctr+1 << endl;
       cout << "Product Code: " << stock[ctr].code <<  endl;
       cout << "Product Description: " << stock[ctr].desc << endl;
       cout << "Price: " << stock[ctr].price << endl;
       cout << "------------------------------------------------\n";
   }
}
...
From: Salman Khilji <skhilji@tampabay.rr.com>
Date: 2004/01/06 Tue AM 06:32:27 GMT
To: ged.suse@ntlworld.com
Subject: Re: [suse-programming-e] (C++) Saving / reading structures to / from disk
Sorry I don't have time to give you a complete implementation, but lets see 
what I can pull out of my brain.  the following won't compile, but will give 
you a brief idea as how to read and write a structure to/from disk.  The 
following will NOT work with structure that have embedded pointers in them.
example:
struct Foo {
 float bar;
 int john;
};
Foo array[2];
... populate the array of structs...
FILE * file = fopen("myfile", "w+b");
fwrite(file, array, sizeof(array));  // I know the arguments are wrong here, 
but lookup the docs to correct it.
To read it back, first use fopen call and read it into a char array.
Then do this.
Foo * array;
array = (Foo*) myCharArray;
After this, you should be able to see what the contents of Foo are.
I have an example that does this, but its at my office and I will have to dig 
it out.
Salman
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Re: [suse-programming-e] (C++) Saving / reading structures to / from disk (desperate measures)

Lukacs Zsolt