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file updation

closed account (1vf9z8AR)
What's wrong with this file updation
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   cout<<"Update your file"<<endl;
  string sh;
  cout<<"Enter character to search";cin>>sh;
  cout<<endl;
  fstream r2;
  r2.open("marks.dat",ios::in|ios::out|ios::binary);;
  r2.seekg(0);
  while(r2>>line)
  {
          if(line==sh)
          {
                cin>>name;
                cin>>rollno;
          }
          r2<<name<<rollno;
  }
  r2.close();


If you want full code here it is
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#include<iostream>
#include<fstream>
#include<string.h>
using namespace std;
int main()
{
    fstream w1;
    w1.open("marks.dat",ios::out|ios::binary);
    char name[80],ans;
    int rollno;
  do
  {
          cout<<"Enter name";cin>>name;
          cout<<endl;
          cout<<"Enter roll number";cin>>rollno;
          cout<<endl;
          w1<<name<<'\t'<<rollno<<'\n';
          cout<<"Enter more records?(y/n)";cin>>ans;
          cout<<endl;
  }while(ans=='y');
w1.close();

  cout<<"Contents of your file"<<endl;
  string line;
  fstream r1;
  r1.open("marks.dat",ios::in|ios::binary);
  r1.seekg(0);
  while(r1>>line)
  {
          cout<<line;
          cout<<endl;
  }
  r1.close();

  cout<<"Update your file"<<endl;
  string sh;
  cout<<"Enter character to search";cin>>sh;
  cout<<endl;
  fstream r2;
  r2.open("marks.dat",ios::in|ios::out|ios::binary);;
  r2.seekg(0);
  while(r2>>line)
  {
          if(line==sh)
          {
                cin>>name;
                cin>>rollno;
          }
          r2<<name<<rollno;
  }
  r2.close();

 cout<<"Contents of your file"<<endl;
  string liner;
  fstream r3;
  r3.open("marks.dat",ios::in|ios::binary);
  r3.seekg(0);
  while(r3>>liner)
  {
          cout<<liner;
          cout<<endl;
  }
  r3.close();
}

Last edited on
ne555 (10692)
> What's wrong with this file updation
¿symptoms?
closed account (1vf9z8AR)
in place of original roll no entered new name+roll are displayed
ne555 (10692)
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  while(r2>>line)
  {
          if(line==sh)
          {
                cin>>name;
                cin>>rollno;
          }
          r2<<name<<rollno; //this always execute
  }
you are overwritting all the records with `name' and `rollno'
when you do `r2>>line' your position is at the end of the word, that's where you start writting.
¿why did you open the file in binary mode? ¿how much space do you hae in each register?
closed account (1vf9z8AR)
oh ok i got it now
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