Rewriting a text file in c++

Question

Working on a program dealing with file stream. I am wanting to edit a line of text that is stored in a text file. To my understanding, the best way to do this would be to copy everything from the original file and over-write it in a new file, making my edits along the way. I haven't been able to find a clear example online, and was wondering if I could see one.

example text file contains:

user1 pass1 55

user2 pass2 56

user3 pass3 57

I would like to edit to to where it has:

user1 pass1 55

user2 pass2 44

user3 pass3 57

Here is my abridged code for context:

#include <iostream>
#include <fstream>

using namespace std;
//function prototypes
void addUser();
void part1();
int main();

//global variables
    string username;
    string password;
    int balance;
void addUser(){
    //open a file in write mode
        ofstream myfile;
        myfile.open("userinfo.txt", ios::app);//append the text file
        if(myfile.is_open()){
        cout<<"Please Create a Username: ";
        string inputCheck;//a string to compare name
        cin>>inputCheck;
        cout<<"Please Create a Password: ";
        cin>>password;
        cout<<"Current Balance: ";
        cin>>balance;
        myfile<<inputCheck<<' '<<password<<' '<<balance<<"\n";
        myfile.close();
        cout<<"User account '"<<inputCheck<<"' has been created"<<endl;
        }//ends create a password else
    part1();
}

void part1()
{
    cout<<"1.Add User\n2.Edit Information"<<endl;
    int input;
    cin>>input;
    if(input == 1){
        addUser();
    }else if(input == 2){
    //find the user
    cout<<"Enter the username: ";
    string checkUser;
    cin>>checkUser;
    ifstream infile("userinfo.txt"); //CREATING IFSTREAM
    ofstream outfile("pleasework.txt");
    bool foundUser = false;
    while(infile>>username>>password>>balance){
        if(checkUser==username){
        foundUser = true;
        break;
        }
    }
    if(foundUser){
    cout<<"Current Balance: "<<balance<<endl;
    cout<<"Enter new balance: ";
    int newBalance;
    cin>>newBalance;    
    if(infile.is_open()){
        outfile<<username<<' '<<password<<' '<<newBalance<<endl;
        //How do I get all of the other unedited accounts in here?!?!?!?!
        }
    }//end input 2
        infile.close();
outfile.close();
    }

}//end part 1

int main(){
    part1();
}

Answer 1

Here is some pseudocode that might help:

Method 1:

open existing file in 'read' mode
open new file in 'write' mode
for each line in existing:
    if line doesn't need update:
        write line to new file
    else:
        make changes to values from line
        write updated line to new file
close existing file
close new file
move new file over existing file

Method 2:

open existing file in 'read/write' mode
data = array of lines
for each line in existing:
    read values into data
clear existing file
add/delete rows in data if necessary
for each row in data:
    update values in row
    write updated line to existing file
close existing file