(C++) Saving / reading structures to / from disk (desperate measures)

6 Jan 2004

      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 
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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(C++) Saving / reading structures to / from disk (desperate measures)

ged.suse＠ntlworld.com