Thread: Binary file trouble

Hi, I hope someone here can shed some light on a problem I'm having.

The simple program below reads a registry number and a name associated with it from the keyboard.

Upon exiting, all of the file contents are printed to the screen, this is working fine.

Accessing a specific name using the registry number doesn't work for some reason but for the life of me I can't figure it out.
Hope someone can take a look and help. Thanks.

Code:

#include <conio.h>
#include <iostream.h>
#include <fstream.h>
#include <cstdlib>

using namespace std;

class info {
      private :
              int regnum,status;
              char name[50];
      public : 
             int checkreg(int);
             void write_name(int);
             void read_name();
             void print_all();
             };
fstream A;

info names;

int info::checkreg(int n)
{
    A.open("c:\\names.dat",ios::in|ios::binary);
    A.clear();
    if(A.good())
    {
     
    int flag=1;
    while(A.read((char*)&names,sizeof(info))&&n!=regnum);
     if(n==regnum&&status)
      flag=0;
     A.close();
     return flag;
}
else cout<<"\nUnable to open file for checkreg";

}

void info::write_name(int n)
{
 A.open("c:\\names.dat",ios::out|ios::binary|ios::app);
 A.clear();
 if(A.good())
  {
 
 regnum=n;
 cout<<"\nEnter Name : ";
 cin>>name;
 status=1;
 A.write((char*)&names,sizeof(info));
 A.close();
 cout<<"\nRegistry saved to file";
}
else cout<<"\nUnable to open file for write";
}

void info::read_name()
{
 A.open("c:\\names.dat",ios::in|ios::binary);
 A.clear();
 if(A.good())
  {
  

 int num;
 cout<<"\nEnter the registry number : ";
 cin>>num;
 
 while(A.read((char*)&names,sizeof(info))&&num!=regnum)
 {
  if(num==regnum&&status)
  {                     
   cout<<"Name : "<<name;
   
}
 
  else cout<<"\nRegistry not found";
 }
 A.close();
}
else cout<<"\nUnable to open file to read";
}

void info::print_all()
{
 A.open("c:\\names.dat",ios::in|ios::binary);
 while(A.read((char*)&names,sizeof(info)))
 {
  cout<<"\n\n";
  cout<<"\nRegnum = "<<regnum;                                        
  cout<<"\nName = "<<name;
 
}
}

int main(void)
{
  int num;
  char option;
  do{
       system("cls"); 
       cout<<"\na - Write to file : ";
       cout<<"\nb - Check a registry : ";
       cout<<"\nc - exit and output all entries : ";
       cout<<"\n\nEnter a b or c: ";
       option=getche();
       switch(option)
       {
                     case 'a':
                          do{
                              cout<<"\nEnter registry number : ";
                              cin>>num;
                              if(names.checkreg(num))
                              {
                               names.write_name(num);
                               
                               }
                              else cout<<"\nThis registry already exists";
                              cout<<"\nWould you like to enter another name? (y/n)";
                              }while(getche()!='n');
                              cout<<"\n";
                             getch();
                              break;
                              
                     case 'b' : names.read_name();
                                cout<<"\n";
                                getch();
                                break;
                     case 'c' : break;
                     default : cout<<"\nThis option doesnt exist";
                     }
                     }while(option!='c');
                     
                     names.print_all();
                     getch();
                     return 0;
}

The problem specifically in the member function : void info::read_name(), can't get the screen output here.

What compiler are you using?? Your program will not compile with VC++ 6.0 because you are mixing obsolete header files with "using namespace std;". Remove the .h extension from iostream and fstream.

you can get rid of conio.h, which isn't portable anyway. replace getche() with cin.get().

Accessing a specific name using the registry number doesn't work for some reason

The while loop is incorrect. try something like this

Code:

void info::read_name()
{
 A.open("c:\\names.dat",ios::in|ios::binary);
 A.clear();
 if(A.is_open())
 {
  

 int num;
 bool found = false;
 cout<<"\nEnter the registry number : ";
 cin>>num;
 cout << endl; 
 while(A.read((char*)&names,sizeof(info)) && !found)
 {
  if(num==regnum)
  {                     
   cout<<"Name : "<<name;
   found = true;
  }
 
 }
 A.close();
 if(!found)
 {
  cout<<"Registry not found" << endl;
 }
}
else cout<<"\nUnable to open file to read";
cout << endl << "Press <Enter> when ready to continue" << endl;
cin.ignore();
}