如何在 C++ 中使用计时器在给定时间内强制输入？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/28944972/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to use a timer in C++ to force input within a given time?
提问by Ankita Rane
I want to implement a time out feature in C++.
我想在 C++ 中实现超时功能。
If the user does not input the value within 2 seconds then the program must display the time-out statement and ask the input again
如果用户没有在 2 秒内输入值，则程序必须显示超时语句并再次询问输入
EX(OUTPUT SCREEN):
EX（输出屏幕）：
Timer=0;
Please enter the input: //if input is not given within 2 seconds then
Time-out: 2 seconds
Timer again set to 0
Please enter the input: //if input is not given within 2 seconds then
Time-out: 2 seconds
Timer again set to 0
Please enter the input:22
Data accepted
Terminate the program`
Code:
代码：
#include<iostream>
#include<time.h>
using namespace std;
int main()
{
clock_t endwait;
endwait = 2000 ;
cout<<endwait;
while (clock() < endwait)
{
cout<<"Please enter the input:";
}
return 0;
}
I have worked on the above code. But this happens only while entering the WHILE loop. How shall i do it in a way so that, I get the required output.
我已经处理了上面的代码。但这只会在进入 WHILE 循环时发生。我该如何做才能获得所需的输出。
回答by Akki
#include <iostream>
#include <thread>
#include <chrono>
#include <mutex>
#include <condition_variable>
using namespace std;
condition_variable cv;
int value;
void read_value() {
cin >> value;
cv.notify_one();
}
int main()
{
cout << "Please enter the input: ";
thread th(read_value);
mutex mtx;
unique_lock<mutex> lck(mtx);
while (cv.wait_for(lck, chrono::seconds(2)) == cv_status::timeout)
{
cout << "\nTime-Out: 2 second:";
cout << "\nPlease enter the input:";
}
cout << "You entered: " << value << '\n';
th.join();
return 0;
}
Output:
输出：
Please enter the input:
Time-Out: 2 second:
Please enter the input:
Time-Out: 2 second:
Please enter the input:22
You entered: 22
回答by edmz
I am afraid, it is not possible in a standard way because I/O operations will block, by default, the calling process until it's finalized or an error is encountered.
You could work it around by creating a thread which checks whether the input has been completed and go sleeping, if needed. But that's not really practical.
恐怕以标准方式是不可能的，因为默认情况下，I/O 操作会阻塞调用进程，直到它完成或遇到错误。
您可以通过创建一个线程来解决它，该线程检查输入是否已完成并在需要时进入睡眠状态。但这并不实际。
The issue lies in the abstraction iostream/FILEs give you: you don't have access to the underlying source, the one the OS "understands" as well and therefore capable to give you that kind of functionality (namely, I/O polling).
问题在于抽象iostream/ FILEs 给您：您无法访问底层源代码，操作系统也“理解”并因此能够为您提供这种功能（即 I/O 轮询）。
回答by Ben Voigt
A separate thread is not enough, because the console read function is still running after the timeout occurs.
单独的线程是不够的，因为发生超时后控制台读取功能仍在运行。
On POSIX you could set a timer which produces a signal and causes the read to fail with -EINTR.
在 POSIX 上，您可以设置一个计时器，该计时器会产生一个信号并导致读取失败-EINTR。
On Windows you can implement low-level console I/O timeouts with ReadConsoleInputand WaitForSingleObject... but then you need to do your own line-buffering.
在 Windows 上，您可以使用ReadConsoleInputand实现低级控制台 I/O 超时WaitForSingleObject……但是您需要进行自己的行缓冲。
Another idea would be to use ReadFilein OVERLAPPEDmode and wait on the completion event with a timeout, but that doesn't work for consoles, see Using overlapped IO for console input?
另一个想法是ReadFile在OVERLAPPED模式下使用并等待超时完成事件，但这不适用于控制台，请参阅使用重叠 IO 进行控制台输入？
Finally, new Windows versions (Vista and later) allow you to overcome the "blocking read is not cancelled by timeout" problem using CancelIoEx. If you call that from a separate thread, it will trigger ReadFileto return early; you won't have to implement line-buffering yourself.
最后，新的 Windows 版本（Vista 及更高版本）允许您使用CancelIoEx. 如果你从一个单独的线程调用它，它会触发ReadFile提前返回；您不必自己实现行缓冲。
回答by Akash
I think there is no need to use complex code (multithreading or mutex) for this purpose. See the code below :
我认为没有必要为此使用复杂的代码（多线程或互斥）。请参阅下面的代码：
#include <iostream>
#include <time.h>
#include <conio.h>
using namespace std;
int main()
{
int numInput;
clock_t start = clock();
cout << "Timer: 2 sec"<<endl;
cout << "Please enter the input: ";
while ( ! _kbhit() ) //Check for keyboard hit
{
//Check if 2 sec timer expired or not
if (((clock () - start)/ CLOCKS_PER_SEC ) >= 2)
{
cout << "\nTimeout 2 sec . . ." << endl;
cout << "Please enter the input: ";
start = clock(); //Set new timer
}
}
//Get the input here
cin >> numInput;
cout << "Data accepted: " << numInput << endl;
_getch();
return 0;
}
回答by Naman Gupta
I have used kbhit() function to solve your problem. The code is as follows:-
我已经使用 kbhit() 函数来解决您的问题。代码如下：-
#include <conio.h>
#include <iostream>
#include <windows.h>
using namespace std;
int main()
{
int i;
DWORD start_time, check_time;
start_time=GetTickCount();
check_time=start_time+2000;
while(!kbhit())
{
cout<<"Please enter the input:"<<endl;
while((check_time>GetTickCount()))
{
if (kbhit())
{
i=getch();
cout<<"Data accepted"<<endl;
return 0;
}
}
cout<<"Time-out: 2 seconds"<<endl;
cout<<"Timer again set to 0"<<endl;
start_time=GetTickCount();
check_time=start_time+2000;
}
return 0;
}
