fstream

May 8, 2014 at 4:28am
CodingisFun (40)
My question is when i inside a thing to file but the file didnt update ? But it did display on code when i run it again.

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#include<string>
#include<fstream>
#include<iomanip>
#include<iostream>

using namespace std;

struct Database_struct
{
    int id;
    char name[100];
    int quant;
    double cost;
};
typedef struct Database_struct Database;
void write_to_binary_file(Database *p_Data);
void read_from_binary_file(Database *p_Data);
void print_records(Database *p_Data);

int main()
{
    int i,j;
    Database d;
    Database db[100],
    temp[8]={
        3,"Electric Sander",7,57.98,
        17,"Hammer",76,11.99,
        24,"Jig Saw",21,11.00,
        39,"Lawn Mover",3,79.50,
        56,"Power Saw",18,99.99,
        68,"Screw-driver",106,6.99,
        77,"Sledge Hammer",11,21.50,
        83,"Wrench",34,7.50
    };
    int n;
    ifstream myfile ("hardware.dat");
    if (myfile.is_open())
    {
        myfile.close();
        cout<<" Database is present, so loading:"<<endl;
        read_from_binary_file(db);
    }
    else
    {
        cout<<"Creating new Database :";
        for(i=0;i<100;i++)
        {
            for(j=0;j<8;j++)
            {
                if(temp[j].id == i)
                {
                    memcpy(&db[i],&temp[j],sizeof(Database));
                    break;
                }
            }
            if(j>=8)
            {
                memset(&db[i],0,sizeof(Database));
            }
        }

        write_to_binary_file(db);
    }
    while(1)
    {
        cout<<"\n1.Display\n2.Insert\n3.Update\n4.Delete\n5.Exit\n";
        cin>>n;
        switch(n)
        {
            case 1:
                print_records(db);
                break;
            case 2:
            again:
                cout<<"Enter the record number:";
                cin>>d.id;
                if(db[d.id].name[0]!=0)
                {
                    cout<<"\nThis id is present in Data Base, so enter other:\n";
                    goto again;
                }
                cout<<"Enter the name:";
                do
                {
                    cin.getline(d.name,sizeof(d.name));
                }while(strcmp(d.name,"")==0);
                cout<<"Enter the Quant:";
                cin>>d.quant;
                cout<<"Enter th cost:";
                cin>>d.cost;
                memcpy(&db[d.id],&d,sizeof(Database));
                write_to_binary_file(db);
                break;
            case 3:
            again1:
                cout<<"Enter the record number:";
                cin>>d.id;
                if(db[d.id].name[0]==0)
                {
                    cout<<"\nThis id is empty so can't update, so enter other:\n";
                    goto again1;
                }
                cout<<"Enter the name:";
                do
                {
                    cin.getline(d.name,sizeof(d.name));
                }while(strcmp(d.name,"")==0);
                cout<<"Enter the Quant:";
                cin>>d.quant;
                cout<<"Enter th cost:";
                cin>>d.cost;
                memcpy(&db[d.id],&d,sizeof(Database));
                write_to_binary_file(db);
                break;
            case 4:
            again2:
                cout<<"Enter the record number:";
                cin>>d.id;
                if(db[d.id].name[0]==0)
                {
                    cout<<"\nThis id is empty so can't delete, so enter other:\n";
                    goto again2;
                }
                memset(&db[d.id],0,sizeof(Database));
                write_to_binary_file(db);
                break;
        }
        if(n==5)
            break;
        
}
}
void write_to_binary_file(Database *p_Data)
{
    int i;
    fstream binary_file("hardware.dat",ios::out|ios::binary);
    if(binary_file.is_open())
    {
        for(i=0;i<100;i++)
        {
            binary_file.write((char*)(&p_Data[i]),sizeof(Database));
        }
            binary_file.close();
        
        }else
        {
            cout<<"\nCan't open file";
        }
}
void read_from_binary_file(Database *p_Data)
{
        fstream binary_file("hardware.dat",ios::binary|ios::in);
        
        binary_file.read((char*)p_Data,sizeof(Database)*100);
        binary_file.close();
        
}
void print_records(Database *p_Data)
{
    int i;
        
    cout<<setw(20)<<"Record"<<setw(20)<<"Tool name"<<setw(20)<<"Quantity"<<setw(20)<<"Cost"<<endl;
    for(i=0;i<100;i++)
    {
        if(p_Data[i].name[0]!=0)
            cout<<setw(20)<<p_Data[i].id<<setw(20)<<p_Data[i].name<<setw(20)<<p_Data[i].quant<<setw(20)<<p_Data[i].cost<<endl;
    }
}

//print_records(db);
//cout<<endl;
Edit & run on cpp.sh


here is files

3 ElectricSander 7 57.98
17 Hammer 76 11.99
24 JigSaw 21 11.00
39 LawnMower 3 79.50
56 PowerSaw 18 99.99
68 Screwdriver 106 6.99
77 SledgeHammer 11 21.50 
83 Wrench 34 7.50
May 8, 2014 at 9:13am
coder777 (8449)
My question is when i inside a thing to file but the file didnt update ? But it did display on code when i run it again.
What makes you think that the data isn't written to the file?
By the way: What you print is the array. It exists independently from the file.

That you always print/write 100 isn't the best idea. That way you print/write data that is invalid.
May 8, 2014 at 6:27pm
CodingisFun (40)
What you mean?
May 8, 2014 at 6:34pm
AbstractionAnon (6954)
What if you have only 80 items in db? You print 100. What is going to print for the last 20 since you're using 100 as your loop limit, not the number actually present.
May 9, 2014 at 2:29am
CodingisFun (40)
when i try to hide a file to see if it read from file. When I do, it still same thing like it dont need file. I want to to read from file
May 9, 2014 at 7:59am
coder777 (8449)
Ok, I see that you set invalid records to 0 so that you don't show them.

What you have to do is this:
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void read_from_binary_file(Database *p_Data)
{
        fstream binary_file("hardware.dat",ios::binary|ios::in);
        
        memset(p_Data,0,sizeof(Database)*100);
        binary_file.read((char*)p_Data,sizeof(Database)*100);
        binary_file.close();
        
}
May 9, 2014 at 4:04pm
CodingisFun (40)
OK I will try. Here is other problems. is I need to change the file from. Txt. To .bin
Last edited on May 9, 2014 at 4:04pm
May 9, 2014 at 4:13pm
CodingisFun (40)
coder777:When i put that in there my complier say:Segmentation Fault (core dumped)
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