How to skip cin on purpose in C++? - c++

Question

I need to have a while-loop running and accept input to it whenever there is an input. I'm not new to C++, but this hurdle is quite difficult. Due to an NDA (this school project is apparently some secret stuff) I can only show you the test case.
I've been grasping for straws trying to solve the problem; try catch, cin.get, cin.peek, if(cin.peek){}. If anybody can point me in the right direction I would be very grateful!
The program is not time-critical, but a function needs to be called with a fixed interval. It is not essential that the code is portable, that it is a while-cin-combination or anything like that; the code will only ever run on a Windows 7 or Windows 8 PC with at least dual core processor.
#include <iostream>
#include <ctime>
using namespace std;
int main()
{
int input = 0;
int pastTime, nowTime;
pastTime = nowTime = time(0);
cin >> input;
while(input != -1)
{
if(input == 1)
{
cout << "Entered 1" << endl;
//To be done instead of the two 'elses',
//bypassing interval-dependant code
}
else if(input == 2)
{
cout << "Entered 2" << endl;
//To be done instead of the interval-dependant code
}
else if(pastTime == (nowTime - 5))
{
cout << "Nothing entered." << endl;
//Needs to be done with a fixed interval.
}
nowTime = time(0);
cin >> input;
}
return 0;
}
The solution was, based om James Beilby's link:
// This program is based on counter.cpp from Boost\lib\thread\tutorial
#include <boost/thread/thread.hpp>
#include <iostream>
#include <ctime>
int timeNow = time(0);
int timePast = time(0);
void fct_one()
{
while(1) //keeps running all the time
{
if(timePast == (timeNow - 3)) // only executed once every three seconds
{
//do some stuff
timePast = time(0);
}
timeNow = time(0); // time is continuously updated
}
}
void fct_two()
{
int input = 0;
int timeTemp = time(0);
while(1) //keeps running all the time
{
std::cin >> input; // cin blocking for input
if(input == 1)
{
//do some stuff
}
if(input == 2)
{
//do some stuff
}
if(input == -1)
{
std::cout << "Program is done. ";
system("pause");
exit(1);
}
}
}
int main()
{
boost::thread_group threads;
threads.create_thread(&fct_one)
threads.create_thread(&fct_two);
threads.join_all();
return 0;
}

Answer 1

I would completely separate reading input from cin and performing the default timeout function. You'll need something like a background thread that performs the default function based on the time interval. To handle the 1st two cases you'll need to signal the thread skipping the next execution (if this is really necessary), and just call any function you want or do nothing.

Answer 2

The simple answer is to put the code that runs at some interval on another thread. Since you've noted this is Windows, you could use a Timer Queue:
Begin with routines to start and stop your time dependent work:
HANDLE Start(HANDLE hTimerQueue)
{
DWORD timerMS = 5000; /* every 5 seconds */
HANDLE hTimer;
if (!CreateTimerQueueTimer(&hTimer,
hTimerQueue,
(WAITORTIMERCALLBACK)timerWork,
/*lpParam*/NULL,
/*start in ___ ms:*/0,
/*run every __ ms:*/timerMS,
/*flags*/0))
{
return NULL;
}
return hTimer;
}
BOOLEAN Stop(HANDLE hTimerQueue, HANDLE hTimer)
{
if (!DeleteTimerQueueTimer(hTimerQueue,
hTimer,
/*wait for our timer to complete*/INVALID_HANDLE_VALUE))
{
return FALSE;
}
return TRUE;
}
Then put your time dependent work into its own callback:
VOID CALLBACK timerWork(PVOID lpParam, BOOLEAN TimerOrWaitFired /*ignored*/)
{
for (int ii = 0; ii < 10; ++ii) {
std::cout << "timer work: " << ii << std::endl;
Sleep(250);
}
}
Finally, integrate these into your workflow:
int main(int argc, char* argv[])
{
HANDLE hTimerQueue = CreateTimerQueue(hTimerQueue);
if (NULL == hTimerQueue) return -1;
HANDLE hTimer = Start(hTimerQueue);
if (NULL == hTimer) return -1;
/* our timed callback is now running in the background */
int input = 0;
std::cin >> input;
while(input != -1)
{
if(input == 1)
{
if (Stop(hTimerQueue, hTimer)) {
std::cout << "Entered 1" << std::endl;
if (NULL == (hTimer = Start(hTimerQueue))) return -2;
}
}
else if(input == 2)
{
if (Stop(hTimerQueue, hTimer)) {
std::cout << "Entered 2" << std::endl;
if (NULL == (hTimer = Start(hTimerQueue))) return -2;
}
}
std::cin >> input;
}
DeleteTimerQueue(hTimerQueue);
return 0;
}