Waits for the result to become available. Blocks until specifiedtimeout_duration has elapsed or the result becomes available, whichever comes first. The return value identifies the state of the result.

If the future is the result of a call tostd::async that used lazy evaluation, this function returns immediately without waiting.

This function may block for longer thantimeout_duration due to scheduling or resource contention delays.

The standard recommends that a steady clock is used to measure the duration. If an implementation uses a system clock instead, the wait time may also be sensitive to clock adjustments.

The behavior is undefined ifvalid() isfalse before the call to this function.

[edit]Parameters

[edit]Return value

[edit]Exceptions

Any exception thrown by clock, time_point, or duration during the execution (clocks, time points, and durations provided by the standard library never throw).

[edit]Notes

The implementations are encouraged to detect the case whenvalid==false before the call and throw astd::future_error with an error condition ofstd::future_errc::no_state.

[edit]Example

#include <chrono>#include <future>#include <iostream>#include <thread>usingnamespace std::chrono_literals; int main(){std::shared_future<int> future=std::async(std::launch::async,[](){std::this_thread::sleep_for(3s);return8;}); std::cout<<"waiting...\n";std::future_status status; do{switch(status= future.wait_for(1s); status){casestd::future_status::deferred:std::cout<<"deferred\n";break;casestd::future_status::timeout:std::cout<<"timeout\n";break;casestd::future_status::ready:std::cout<<"ready!\n";break;}}while(status!=std::future_status::ready); std::cout<<"result is "<< future.get()<<'\n';}

waiting...timeouttimeouttimeoutready!result is 8

[edit]See also

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