Wait for key press but auto-start after time C++ - c++

Question

I've seen this answered for other languages but not for C++. How would I get a program to wait for the user to press Enter or some key like that, but also to automatically continue after a set time period as long as a key hasn't been entered? I need basic code, I'm sort of a beginner. I know that cin.get(); or system("pause"); will wait for a key and sleep(x seconds); or Sleep(x milliseconds); (with the "windows.h" library) will pause a program, but how do I get both at once?

Answer 1

In windows you can use GetAsyncKeyState() to poll the current state of the keyboard. Then you can use Sleep() to sleep a certain number of milliseconds. Combine those two and you can make something like what you need:
int keyToWaitFor = VK_SPACE;
int count = 0;
int maxcount = 500;
for(int a = 0; a < maxcount; a++){
if (GetAsyncKeyState(keyToWaitFor)!=0){
break;
}
Sleep(5);
}

Answer 2

Since you apparently want to do this on Windows, it's fairly straightforward.
You start by opening a handle to the console, such as with GetStdHandle. Then when you want to do a read, you call WaitForSingleObject on that handle, specifying your timeout value. Check the return. If the return value is WAIT_OBJECT_0, it means you have some input, which you can read with (for example) ReadConsoleInput. If the return is WAIT_TIMEOUT, it means there's no input, so you can do whatever else it is you want to do.

Answer 3

With conio.h, You can wait for a keypress with kbhit() and getch() and make a wait for a 20 second timer with a
while loop, while( key==0 && (time_to_wait < secs) ).
#include <iostream>
#include <cstdio>
#include <ctime>
#include <conio.h>
#include <windows.h>
using namespace std;
int key=0;
bool quit=false;
void check_if_keypressed();
void gotoxy(int x, int y);
void clrscr();
int main()
{
clock_t start;
double time_to_wait;
double secs=10;
gotoxy(1, 2);
cout<<"Press any key to continue or wait 20 seconds: \n ";
start = clock();
while( key==0 && (time_to_wait < secs) )
{
check_if_keypressed();
time_to_wait = ( clock() - start ) / (double) CLOCKS_PER_SEC;
// proceed with whatever here
gotoxy(1, 23);
cout<<"countdown: "<< secs-time_to_wait <<" \n ";
}
// proceed with whatever here
// while( key!=27)
// {
// check_if_keypressed();
// do_other_stuff();
// }
return 0;
}
void check_if_keypressed()
{
if( kbhit() ) key=getch();
switch(key)
{
case 27:
quit=true;
break;
}
}
void gotoxy(int x, int y)
{
COORD coord;
coord.X = x; coord.Y = y;
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), coord);
return;
}
void clrscr()
{
COORD coordScreen = { 0, 0 };
DWORD cCharsWritten;
CONSOLE_SCREEN_BUFFER_INFO csbi;
DWORD dwConSize;
HANDLE hConsole = GetStdHandle(STD_OUTPUT_HANDLE);
GetConsoleScreenBufferInfo(hConsole, &csbi);
dwConSize = csbi.dwSize.X * csbi.dwSize.Y;
FillConsoleOutputCharacter(hConsole, TEXT(' '), dwConSize, coordScreen, &cCharsWritten);
GetConsoleScreenBufferInfo(hConsole, &csbi);
FillConsoleOutputAttribute(hConsole, csbi.wAttributes, dwConSize, coordScreen, &cCharsWritten);
SetConsoleCursorPosition(hConsole, coordScreen);
return;
}