C++program to delete the content of a Binary File

11 Nov, 2019
This article explains how to delete the content of a Binary File.
Given a binary file that contains the records of students, the task is to delete the record of the specified student. If the record of no such student exists, then print “record not found”.
Examples:
Input:
roll no: 1
Output
The deleted record is 
roll no: 1
name: vinay
record successfully deleted

Input:
roll no: 2
Output:
record not found 

Approach:In this example, the existing roll number of the student whose record is to be deleted is taken from the user and we will create a new file in which we will write all the records of the first file except the record to be deleted and then delete the first file and rename new file with the name of the first file
Below are the various steps on how to do so:
Step 1:Opening the file from which the record is to be deleted in reading mode here “he.dat”
Step 2: Opening the file to which the new content is to be written in writing mode here “temp.dat”
Step 3:Reading the file and Comparing the record roll no with that to be deleted
Step 4: If during reading the roll number to be deleted exists then display it else write the record in temp.dat
Step 5: Finally after reading the complete file delete the file “he.dat” and rename the new file “temp.dat” with “he.dat”
Step 6: If in the file record exist then print the record and print record successfully deleted
Step 7: If the roll number does not exists then print “record not found”.
Standard Library Functions used:
// to remove the file
remove("name_of_file");

// to rename file1 as file2
rename("name-of_file1", "name_of_file2");

Below is the implementation of the above approach:
// C++ program to delete the record// of a binary file  #include <bits/stdc++.h>  using namespace std;  class abc {    int roll;    char name[20];  public:    void deleteit(int);    void testcase1();    void testcase2();    void putdata();};  // Code to display the data of the// data of the objectvoid abc::putdata(){    cout << "roll no: ";    cout << roll;    cout << "\nname: ";    cout << name;}  // code to delete// the content of the binary filevoid abc::deleteit(int rno){      int pos, flag = 0;      ifstream ifs;    ifs.open("he.dat", ios::in | ios::binary);      ofstream ofs;    ofs.open("temp.dat", ios::out | ios::binary);      while (!ifs.eof()) {          ifs.read((char*)this, sizeof(abc));          // if(ifs)checks the buffer record in the file        if (ifs) {              // comparing the roll no with            // roll no of record to be deleted            if (rno == roll) {                flag = 1;                cout << "The deleted record is \n";                  // display the record                putdata();            }            else {                // copy the record of "he" file to "temp" file                ofs.write((char*)this, sizeof(abc));            }        }    }      ofs.close();    ifs.close();      // delete the old file    remove("he.dat");      // rename new file to the older file    rename("temp.dat", "he.dat");      if (flag == 1)        cout << "\nrecord successfully deleted \n";    else        cout << "\nrecord not found \n";}  // Sample input 1void abc::testcase1(){    int rno;      // roll no to be searched    rno = 1;      // call deleteit function    // with the roll no. of record to be deleted    deleteit(rno);}  // Sample input 2void abc::testcase2(){    int rno;      // roll no to be searched    rno = 4;      // call deleteit function    // with the roll no of record to be deleted    deleteit(rno);}  // Driver codeint main(){    abc s;      // sample case 1    s.testcase1();      // sample case 2      s.testcase2();      return 0;}
Output:
to delete the record of the file
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