std::shared_future::get

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Thread support library

Threads
thread (C++11)
hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)
this_thread namespace
get_id (C++11) yield (C++11)	sleep_for (C++11) sleep_until (C++11)
Mutual exclusion
mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17)	timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14)
Generic lock management
lock_guard (C++11) scoped_lock (C++17) unique_lock (C++11) shared_lock (C++14) defer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11)	lock (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lock (C++11)(C++11)(C++11) once_flag (C++11) call_once (C++11)
Condition variables
condition_variable (C++11)
condition_variable_any (C++11)
notify_all_at_thread_exit (C++11)
cv_status (C++11)
Futures
promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11)	launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11)

std::shared_future

Member functions

shared_future::shared_future

shared_future::~shared_future

shared_future::operator=

Getting the result

shared_future::get

State

shared_future::valid

shared_future::wait

shared_future::wait_for

shared_future::wait_until

const T& get() const;	(1)	(member only of generic shared_future template) (since C++11)
T& get() const;	(2)	(member only of shared_future<T&> template specialization) (since C++11)
void get() const;	(3)	(member only of shared_future<void> template specialization) (since C++11)

The get method waits until the shared_future has a valid result and (depending on which template is used) retrieves it. It effectively calls wait() in order to wait for the result.

The generic template and two template specializations each contain a single version of get. The three versions of get differ only in the return type.

The behavior is undefined if valid() is false before the call to this function.

Parameters

(none)

Return value

1) Const reference to the value stored in the shared state. Accessing the value through this reference is undefined after the shared state has been destroyed.

2) The reference stored as value in the shared state.

3) Nothing.

Exceptions

If an exception was stored in the shared state referenced by the future (e.g. via a call to std::promise::set_exception()) then that exception will be thrown.

Notes

The implementations are encouraged to detect the case when valid() is false before the call and throw a std::future_error with an error condition of std::future_errc::no_state.

See also

valid

checks if the future has a shared state (public member function)