[HELP] C++ random access file

[alfredhin]

I have some problems when i need to delete one record after I enter the number, the problem is
1) no matter which record number I enter(both exist or not exist in the file), it still print out " Record deleted"
2) after that, The record in the file i have stored at the beginning are all become blank.


what's wrong of the code in line 69 to line 86?
how can i modify it?

THANK YOU VERY MUCH

#include <fstream>
#include <iostream>
#include <string>
#include <iomanip>
#include <cstdio>
using namespace std;
struct Store{
	int record;
	char name[20];
	int quantity;
	double cost;
};
int main()
{
	int r;
	int choice;
//--------------Create 100 blank record into a file--------------
	fstream fout("hardware.dat",ios::out|ios::binary);
	Store blankstore={0,"",0,0.0};
	for(int i=0;i<100;i++)
	{
	fout.write(reinterpret_cast<const char*>(&blankstore),sizeof(Store));
	}

//---------------------add record into a file------------------------
	  ofstream outstore("hardware.dat",ios::out|ios::binary);
			while(true)
			{	
			 cout<<"Enter record number.(0 to exit)\n?";
			 cin>>r;
				 while(r>100)
				 {
					 cout<<"The record number should be less than 100\nEnter again: ";
					 cin>>r;
				 }
			 if(r<=0)			
			    {break;}
			 Store store;
			 store.record=r;
			 cout<<"Enter name of tool, quantity and cost.\n?";
			 cin>>store.name>>store.quantity>>store.cost;
			 outstore.seekp((store.record-1)*sizeof(Store));
		     outstore.write(reinterpret_cast<const char*>(&store),sizeof(Store));
			}
			outstore.close();
//-----------------Ask for choice----------------------------
		cout<<"Enter choice: ";
		cin>>choice;
	while(choice>0 && choice<5)
	{

	  if(choice ==1)//-----------print out all records form the file-----------------
	  {
			 ifstream instore("hardware.dat",ios::in|ios::binary);
			 cout<<left<<setw(10)<<"Record#"<<setw(12)<<"Tool name"<<setw(10)<<"Quantity"<<"Cost\n";
			Store store;
			 instore.read(reinterpret_cast<char *>(&store),sizeof(Store));
					while(instore&&!instore.eof())
						{
							  if(store.record!=0)
								cout<<left<<setw(10)<<store.record<<setw(12)<<store.name<<setw(10)
								<<store.quantity<<store.cost<<endl;
						  instore.read(reinterpret_cast<char *>(&store),sizeof(Store));
						}

	   instore.close();
	  }

	else if(choice== 2)//------------ask for one record to be deleted---------
		{
		fstream delstore("hardware.dat",ios::out|ios::binary);
		cout<<"Enter the record number: ";
		cin>>r;
		delstore.seekg((r-1)*sizeof(Store));
		Store store;
		delstore.read(reinterpret_cast<char *>(&store),sizeof(Store));
		if(store.record!=0)
		{
			Store blankStore;
			delstore.seekp((r-1)*sizeof(Store));
			delstore.write(reinterpret_cast<const char*>(&blankStore),sizeof(Store));
			cout<<"Record deleted!\n";
		}
	
		delstore.close();
		}
	 //----------------------------------------------
		cout<<"Enter choice: ";
		cin>>choice;
	}//---------------end fo while-----------
	system("pause");
    return 0;
}

[cire]

Line 71 you open delstore with an openmode of ios::out | ios::binary.

Line 74 you do a seekg() on a file opened only for output.

Line 76 you do a read from a file that is only opened for output.

I'm guessing this may put the object into a bad state. Hard to tell though since you check no return values.

[alfredhin]

ya. you right
the problem is fixed after i add "ios::in" in line 71
so careless ,didn't realize it
thank you very much^^