How do you add a timed delay to a C++ program?

Question

I am trying to add a timed delay in a C++ program, and was wondering if anyone has any suggestions on what I can try or information I can look at?

I wish I had more details on how I am implementing this timed delay, but until I have more information on how to add a timed delay I am not sure on how I should even attempt to implement this.

Answer 1

An updated answer for C++11:

Use the sleep_for and sleep_until functions:

#include <chrono>
#include <thread>

int main() {
    using namespace std::this_thread; // sleep_for, sleep_until
    using namespace std::chrono; // nanoseconds, system_clock, seconds

    sleep_for(nanoseconds(10));
    sleep_until(system_clock::now() + seconds(1));
}

With these functions there's no longer a need to continually add new functions for better resolution: sleep, usleep, nanosleep, etc. sleep_for and sleep_until are template functions that can accept values of any resolution via chrono types; hours, seconds, femtoseconds, etc.

In C++14 you can further simplify the code with the literal suffixes for nanoseconds and seconds:

#include <chrono>
#include <thread>

int main() {
    using namespace std::this_thread;     // sleep_for, sleep_until
    using namespace std::chrono_literals; // ns, us, ms, s, h, etc.
    using std::chrono::system_clock;

    sleep_for(10ns);
    sleep_until(system_clock::now() + 1s);
}

Note that the actual duration of a sleep depends on the implementation: You can ask to sleep for 10 nanoseconds, but an implementation might end up sleeping for a millisecond instead, if that's the shortest it can do.

Answer 2

In Win32:

#include<windows.h>
Sleep(milliseconds);

In Unix:

#include<unistd.h>
unsigned int microsecond = 1000000;
usleep(3 * microsecond);//sleeps for 3 second

sleep() only takes a number of seconds which is often too long.

Answer 3

#include <unistd.h>
usleep(3000000);

This will also sleep for three seconds. You can refine the numbers a little more though.

Answer 4

Do you want something as simple like:

#include <unistd.h>
sleep(3);//sleeps for 3 second

Answer 5

Note that this does not guarantee that the amount of time the thread sleeps will be anywhere close to the sleep period, it only guarantees that the amount of time before the thread continues execution will be at least the desired amount. The actual delay will vary depending on circumstances (especially load on the machine in question) and may be orders of magnitude higher than the desired sleep time.

Also, you don't list why you need to sleep but you should generally avoid using delays as a method of synchronization.

Answer 6

You can try this code snippet:

#include<chrono>
#include<thread>

int main(){
    std::this_thread::sleep_for(std::chrono::nanoseconds(10));
    std::this_thread::sleep_until(std::chrono::system_clock::now() + std::chrono::seconds(1));
}

Answer 7

You can also use select(2) if you want microsecond precision (this works on platform that don't have usleep(3))

The following code will wait for 1.5 second:

#include <sys/select.h>
#include <sys/time.h>
#include <unistd.h>`

int main() {
    struct timeval t;
    t.tv_sec = 1;
    t.tv_usec = 500000;
    select(0, NULL, NULL, NULL, &t);
}

`

Answer 8

I found that "_sleep(milliseconds);" (without the quotes) works well for Win32 if you include the chrono library

E.g:

#include <chrono>

using namespace std;

main
{
    cout << "text" << endl;
    _sleep(10000); // pauses for 10 seconds
}

Make sure you include the underscore before sleep.

Answer 9

Yes, sleep is probably the function of choice here. Note that the time passed into the function is the smallest amount of time the calling thread will be inactive. So for example if you call sleep with 5 seconds, you're guaranteed your thread will be sleeping for at least 5 seconds. Could be 6, or 8 or 50, depending on what the OS is doing. (During optimal OS execution, this will be very close to 5.)
Another useful feature of the sleep function is to pass in 0. This will force a context switch from your thread.

Some additional information:
http://www.opengroup.org/onlinepubs/000095399/functions/sleep.html

Answer 10

The top answer here seems to be an OS dependent answer; for a more portable solution you can write up a quick sleep function using the ctime header file (although this may be a poor implementation on my part).

#include <iostream>
#include <ctime>

using namespace std;

void sleep(float seconds){
    clock_t startClock = clock();
    float secondsAhead = seconds * CLOCKS_PER_SEC;
    // do nothing until the elapsed time has passed.
    while(clock() < startClock+secondsAhead);
    return;
}
int main(){

    cout << "Next string coming up in one second!" << endl;
    sleep(1.0);
    cout << "Hey, what did I miss?" << endl;

    return 0;
}

Answer 11

to delay output in cpp for fixed time, you can use the Sleep() function by including windows.h header file syntax for Sleep() function is Sleep(time_in_ms) as

cout<<"Apple\n";
Sleep(3000);
cout<<"Mango";

OUTPUT. above code will print Apple and wait for 3 seconds before printing Mango.

Answer 12

Syntax:

void sleep(unsigned seconds);

sleep() suspends execution for an interval (seconds). With a call to sleep, the current program is suspended from execution for the number of seconds specified by the argument seconds. The interval is accurate only to the nearest hundredth of a second or to the accuracy of the operating system clock, whichever is less accurate.

Answer 13

Many others have provided good info for sleeping. I agree with Wedge that a sleep seldom the most appropriate solution.

If you are sleeping as you wait for something, then you are better off actually waiting for that thing/event. Look at Condition Variables for this.

I don't know what OS you are trying to do this on, but for threading and synchronisation you could look to the Boost Threading libraries (Boost Condition Varriable).

Moving now to the other extreme if you are trying to wait for exceptionally short periods then there are a couple of hack style options. If you are working on some sort of embedded platform where a 'sleep' is not implemented then you can try a simple loop (for/while etc) with an empty body (be careful the compiler does not optimise it away). Of course the wait time is dependant on the specific hardware in this case. For really short 'waits' you can try an assembly "nop". I highly doubt these are what you are after but without knowing why you need to wait it's hard to be more specific.

Answer 14

On Windows you can include the windows library and use "Sleep(0);" to sleep the program. It takes a value that represents milliseconds.