Функции seekg, clear и операция передачи в поток при работе с файлами

while (oldMaster >> accountNumM >> firstName >> lastName >> currentBalance) {
    while (transaction >> accountNumT >> dollarAmount) {
        if (accountNumM == accountNumT) {
            currentBalance += dollarAmount;
        }
    }
    outNewMaster << accountNumM << ' ' << firstName
        << ' ' << lastName << ' ' << currentBalance << endl;
}

transaction.seekg(0);

transaction.clear();

#include <iostream>
#include <fstream>
 
using namespace std;
 
int main()
{
    ofstream fout("tran.txt");
    fout << 1 << ' ' << 2 << ' ' << 3 << ' ' << 4 << ' ' << 5 << endl;
    fout.close();
 
    ifstream transaction("tran.txt");
 
    for (int i = 0; i < 5; ++i)
    {
        for (int n; transaction >> n; )
            cout << n << ' ';
 
        transaction.clear(); // сначала clear, только потом seekg
        transaction.seekg(0);
        cout << endl;
    }
 
    system("pause");
    return 0;
}

using account_t = int;
using amount_t = int;
using name_t = std::string;
using transact_map = std::map<account_t, amount_t>;
 
transact_map load(std::istream& transaction)
{
    transact_map data;
    account_t accountNumT;
    amount_t dollarAmount;
    
    while (transaction >> accountNumT >> dollarAmount) {
        data[accountNumT] += dollarAmount;
    }
    
    return data;
}
 
void update_accounts(
    std::istream& transaction,
    std::istream& oldMaster,
    std::ostream& outNewMaster
)
{
    name_t firstName;
    name_t lastName;
    account_t accountNumM;
    amount_t  currentBalance;
 
    auto data = load(transaction);
    
    while (oldMaster >> accountNumM >> firstName >> lastName >> currentBalance) {
        currentBalance += data[accountNumM];
        outNewMaster << accountNumM << ' ' << firstName
            << ' ' << lastName << ' ' << currentBalance << endl;
    }
}