Library project

[Beginner of C]

hello everyone. I was making a project for college library management system with C++(using file handling and OOPS). I am told to keep a live record of books in a file(.txt or .dat). Now if a book is issued, its count will be lessened by 1. HOW TO UPDATE THE COUNT IN THE TXT OR DAT FILE. E.g. if a book(OBJECT) is issued and it had 22 copies. now it has 21 copies. how to edit update that 22 to 21 in the file. YOU CAN VIEW THE PROJECT I MADE TILL NOW here..... https://github.com/js899/LIBRARY

FUNCTION TO ISSUE BOOK:

cout<<"ENTER ONE MORE INFO";
            string sassy;
            cin>>sassy;
            int found;
            while(fin){
                string s;
                getline(fin, s);
                found = s.find(sassy);
                if(found){
                break;
                }
            }
            if(found!=string::npos){
                cout<<"ISSUED"<<endl;
                    b.nofcopies--;
                    ofstream fout;
                    fout<<b.nofcopies--;
            }
        }

i know this is not correct, just posted it. Please help.

[jonnin]

for small things it is easier to just rewrite the entire file with the updated info.
you could find the exact spot and over-write the file after updating just the affected data but its a bit harder (its easier for binary files to find the right spot to edit. you could make your text file a binary file with fixed width string locations using a sensible over-sized width... pad the extra space with spaces ...

[fiji885]

It is an jonnin said. It's probably much easier for you to just read everything in the file into some class like the below (assuming you haven't learned about binary files).

class Books {
  public:
    // Some getter and setter functions in public
  private:
    std::string authorFirstName;
    std::string authorLastName;
    std::string bookTitle;
    unsigned int copies;
};

Then once you need to access the library, you would just use a getter or setting function to do so. To write or update the library, you would overwrite using the an object from std::ofstream like so:

void updateFunction(Books& obj) {
  // update function to open the file and rewrite everything, thus updating the
  // values
}