c++ function deleting a line - c++

Question

hello guys i'm trying to delete a full line from a ".txt" file when the user enters the book id
my text file looks like this :
[BOOK INFO]%Book Id : 1%title : Object oriented programming%[PUBLISHER
INFO]%publisher name : misr publish house%puplisher address
:adfaf%[AUTHOR(s) INFO]%Authors Name : ahmed%Nationality :
egyptian%Authors Name : eter%Nationality : american%[MORE
INFO]%PublishedAt : 3/3/2006%status :6.
[BOOK INFO]%Book Id : 2%title : automate%[PUBLISHER INFO]%publisher
name : misr%puplisher address :nasr city%[AUTHOR(s) INFO]%Authors Name
: ahmed khaled%Nationality : egyptian%Authors Name : ohammed
adel%Nationality : egyptian%[MORE INFO]%PublishedAt : 3/8/2005%status
:15.
the line starts from [book info] to the (.)
i should be able to delete the whole line when the user enter the id
but i don't know how or what function to use
my code is :
/*password is admin*/
#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>
#include<stdlib.h>
#include<iomanip>
#include<conio.h>
#define F1 59
#define ESC 27
using namespace std;
void list_all_books_1();
void list_available_books_2();
void borrow_books_3();
void search_for_abook_4();
void add_new_book_5();
void delete_books_6();
fstream d_base;
char path[] = "library books.txt";
void output(){
//this function for displaying choices only
cout << setw(77) << "***********************************" << endl;
cout << setw(71) << "1. List all books in library" << endl;
cout << setw(77) << "2. List available books to borrow " << endl;
cout << setw(72) << "3. Borrow a Book from library" << endl;
cout << setw(63) << "4. Search For a Book" << endl;
cout << setw(59) << "5. Add New Books" << endl;
cout << setw(59) << "6. Delete a Book" << endl;
cout << setw(62) << "7. EXIT The Library" << endl;
cout << setw(77) << "***********************************" << endl;
}
//=====================================================================================================================================================
struct books{
//identfying books with all needed things
string id, status;
string title, p_name, p_address;
string date;
};
struct author{
string aut_name;
string aut_nationality;
};
//=====================================================================================================================================================
//function for choice 1 showing the books
void list_all_books_1(){
ifstream show;
char all;
show.open(path, ios::in | ios::app);
while (!show.eof()){
show >> std::noskipws;
show >> all;
if (all == '%')
cout << "\n";
else if (all == '.')
cout << "\n\n\n";
else
cout << all;
}
cout << endl;
show.close();
}
//=====================================================================================================================================================
void list_available_books_2(){
ifstream available_books;
char x;
available_books.open(path, ios::in | ios::app);
while (!available_books.eof()){
available_books >> std::noskipws;
available_books >> x;
if (x == '%')
cout << "\n";
else if (x == '.')
cout << "\n\n\n";
else
cout << x;
}
cout << endl;
available_books.close();
}
//=====================================================================================================================================================
void borrow_books_3(){
}
//=====================================================================================================================================================
void search_for_abook_4(){
string idx;
int offset, i = 0;
string line;
cout << "enter the ID of the book you're looking for";
cin >> idx;
d_base.open(path, ios::in | ios::app);
while (!d_base.eof()){
getline(d_base, line);
if (((offset = line.find(idx, 0))) != string::npos){
cout << "Book found" << endl;
i++;
d_base.close();
}
}
if (i == 0){
cout << "couldn't find book" << endl << endl;
}
}
//=====================================================================================================================================================
//for choice 5 to fill books
void add_new_book_5(){
int aut_number, booksnumber;
books newbook[1000];
author aut[100];
cout << "how many books you want to add ? ";
cin >> booksnumber;
cout << "what books you want to add :" << endl;
d_base.open(path, ios::out | ios::app);
for (int i = 0; i < booksnumber; i++){
cout << "id please : "; cin >> newbook[i].id;
cout << "title : "; cin.ignore(); getline(cin, newbook[i].title);
cout << "publisher name :"; getline(cin, newbook[i].p_name);
cout << "publisher address : "; getline(cin, newbook[i].p_address);
d_base << "[BOOK INFO]" << "%Book Id : " << newbook[i].id << "%title : " << newbook[i].title;
d_base << "%[PUBLISHER INFO]" << "%publisher name : " << newbook[i].p_name << "%puplisher address :" << newbook[i].p_address;
d_base << "%[AUTHOR(s) INFO]";
cout << "how many authors for the books";
cin >> aut_number;
for (int j = 0; j < aut_number; j++){
cout << "author" << j + 1 << " name : "; cin.ignore(); getline(cin, aut[j].aut_name);
cout << "Nationality : "; getline(cin, aut[j].aut_nationality);
d_base << "% Authors Name : " << aut[j].aut_name << "% Nationality : " << aut[j].aut_nationality;
}
cout << "Publish date :"; getline(cin, newbook[i].date);
cout << "How many copies of " << newbook[i].title << " "; cin >> newbook[i].status;
d_base << "%[MORE INFO]";
d_base << "%PublishedAt : " << newbook[i].date << "%status :" << newbook[i].status << "." << endl;
}
d_base.close();
cout <<setw(76)<< "Books Have Been Saved Sucessfully" << endl;
}
//=====================================================================================================================================================
void delete_books_6(){
//deleting a book
}
//=====================================================================================================================================================
int main(){
char choice;
cout << "\n\n" << setw(76) << "{ welcome to FCIS library }\n\n";
do{
output();
cout << "- what do you want to do ? ";
cin >> choice;
if (choice == '1'){
system("cls");
list_all_books_1();
}
//this one for list available books
else if (choice == '2'){
system("cls");
list_available_books_2();
}
//this one for borrow a book
else if (choice == '3'){
system("cls");
borrow_books_3();
}
else if (choice == '4'){
system("cls");
search_for_abook_4();
}
//this one is for adding new books to the list
else if (choice == '5'){
system("cls");
string pass;
do{
cout << "you must be an admin to add new books." << endl << "please enter passowrd (use small letters) : ";
cin >> pass;
if (pass == "b")
break;
else if (pass == "admin"){
system("cls");
cout << "ACCESS GAINED WELCOME " << endl;
add_new_book_5();
}
else{
cout << "Wrong password try again or press (b) to try another choice";
continue;
}
} while (pass != "admin");
}
//this one for deleteing a book
else if (choice == '6'){
system("cls");
//not completed yet
}
else if (choice == '7'){
system("cls");
cout << "\n\n\n"<<setw(76) << "Thanks for Using FCIS LIBRARY" << endl;
break;
}
else
cout << "\nwrong choice please choose again\n\n";
} while (_getch()!=27);
}
i tried to use get line and search for matching id the delete the line if there's match but couldn't accomplish it
i'm beginner at c++ by the way

Answer 1

Read the whole file into a memory buffer. Delete what you don't want. Overwrite the existing file with the contents of your memory buffer.
You've now deleted what you did not want from the file.