asyncFileReader v1.0

#include <bits/stdc++.h>
using namespace std;

string asyncFileReader(string fname, ostream &out = cout) {
    string line, fdata;
    ifstream fin(fname);
    constexpr bool DEMO = true;
    bool finished = false;
    out << "loading";
    auto utilReader = [&]()->void {
        while (getline(fin, line)) {
            fdata += line + '\n';
            if (DEMO) {
                //simulate a large file
                for (int i = 0; i < (int)1e8; i++) {
                    continue;
                }
            }
        }
        finished = true;
        out << endl;
    };
    auto loadingScreen = [&]()->void {
        while (!finished) {
            out << '.';
            this_thread::sleep_for(chrono::milliseconds(100));
        }
    };
    thread t1(utilReader);
    thread t2(loadingScreen);
    t1.join();
    t2.join();//*/
    return fdata;
}

int main() {
    puts(asyncFileReader("text.in").c_str());
    return 0;
}