Terminal Input with timeout (thread + timer + cin) - c++

Question

I want to start a console-program (qt, c++) and ask the user whether he wants to load the previous settings or set new ones. After 10 sec without input, I want to automatically load the settings.
My approach:
start the program with a qTimer and an additional thread
ask the user via std::cin for his input in the additional thread
fire the timer if there is no input to quit the thread and continue the main program
The problem I'm facing is, that I can not abort the std::cin programmatically. Even quitting the Thread would not abort std::cin.
So I guess my approach is not right, what's the best way to achieve my overall goal?

Answer 1

From your mention of threads I'm guessing the intent is to allow the user to enter text at a console prompt without blocking the Qt event loop. That being the case you can probably avoid explicit use of threads all together by making use of QSocketNotifier.
The following example demonstrates the basic idea...
#include <cstdio>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <QCoreApplication>
#include <QSocketNotifier>
#include <QTimer>
int
main (int argc, char **argv)
{
try {
QCoreApplication app(argc, argv);
QTimer timeout;
/*
* Create a QSocketNotifier and let it monitor stdin/std::cin. The
* connected lambda just reads one char at a time here.
*/
QSocketNotifier stdin_notifier(::fileno(stdin), QSocketNotifier::Read);
QObject::connect(&stdin_notifier, &QSocketNotifier::activated,
[&](QSocketDescriptor socket, QSocketNotifier::Type type)
{
/*
* We've received input so stop the timer and read a
* single char.
*/
timeout.stop();
char c;
::read(::fileno(stdin), &c, 1);
std::cout << "stdin: read `" << c << "'\n";
});
/*
* Start with a 5 second timeout.
*/
unsigned remaining = 5;
std::cout << "you have " << remaining << "s to start entering text\r" << std::flush;
QObject::connect(&timeout, &QTimer::timeout,
[&]
{
if (!--remaining) {
std::cout << std::left << std::setfill(' ') << std::setw(50)
<< "too late" << "\n";
app.quit();
} else {
std::cout << "you have " << remaining
<< "s to start entering text\r" << std::flush;
}
});
timeout.start(1000);
exit(app.exec());
}
catch (std::exception &ex) {
std::cerr << ex.what() << "\n";
}
catch (...) {
std::cerr << "unrecognized exception\n";
}
exit(1);
}