Searching in binary file C++

Question

#include <iostream>
#include <fstream>
#include <conio.h>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

class Student{
private:
    char name[40];
    char grade;
    float marks;
public:
    void getdata();
    void display();
    char* getname(){return name;}
    void search(fstream,char*);
};

void Student::getdata(){
    char ch;
    cin.get(ch);
    cout<<"Enter name : ";
    cin.getline(name,40);
    cout<<"Enter grade : ";
    cin>>grade;
    cout<<"Enter marks : ";
    cin>>marks;
    cout<<"\n";
}

void Student::display(){
    cout<<"Name : "<<name<<"\t";
    cout<<"Grade : "<<grade<<"\t";
    cout<<"Marks : "<<marks<<"\t"<<"\n";
}

void search(fstream fin,char* nm)/*initializing argument 1 of 'void search(std::fstream, char*)'*/{
    Student s;
    fin.open("stu.txt",ios::in|ios::binary);
    while(!fin){
        fin.read((char*)&s,sizeof(s));
        if(s.getname()==nm){
            cout<<"Record found !";
            s.display();
            break;
        }
    }
    fin.close();
}

int main(){
    system("cls");
    char nam[40];
    Student arts[3];
    fstream f;
    f.open("stu.txt",ios::in|ios::out|ios::binary);
    if(!f){
        cerr<<"Cannot open file !";
        return 1;
    }
    for(int i=0;i<3;i++){
        arts[i].getdata();
        f.write((char*)&arts[i],sizeof(arts[i]));
    }
    f.close();
    cout<<"Enter name to be searched for : ";
    cin.getline(nam,40);
    char* p = new char[40];
    p=nam;
    search(f,p);/*synthesized method 'std::basic_ios<char>::basic_ios(const std::basic_ios<char>&)' first required here*/
    getch();
    f.close();
    return 0;
}

The above program first creates a file "stu.txt" and writes user-given input to the file. It is then supposed to search for a record based on the name the user enters ( using the search() function ). I'm getting errors when calling search() and also defining search(). I've put in the errors the compiler throws as comment lines. Could anyone explain what's going wrong in there ?

You cannot have a fstream parameter because fstream cannot be copied. Use fstream& instead. — n. m. could be an AI
– n. m. could be an AI, Commented Sep 9, 2014 at 5:53
It passes the stream by reference (look up pass by reference). — n. m. could be an AI
– n. m. could be an AI, Commented Sep 9, 2014 at 5:58

Steve Lorimer · Accepted Answer · 2014-09-09 06:17:38Z

2

fstream is not copyable, so you have to pass fstream as a reference, or in c++11, move it.

Given you access f after calling search, it is best to pass it by reference.

Change your function to accept the fstream as a reference:

void search(fstream& fin,char* nm)

answered Sep 9, 2014 at 6:17

Steve Lorimer

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