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Returns a future object associated with the object's shared state.
The future object returned can access the value or exception set on the shared state by the promise object once this is ready.
Only one future object can be retrieved for each promise shared state.
After this function has been called, the promise is expected to make its shared state ready at some point (by setting a value or an exception), otherwise it is automatically made ready on destruction containing an exception of type future_error (with a broken_promise error condition).
T is the type of the value (the template parameter of promise).
Output
This member function throws an exception on the following conditions:
Depending on the library implementation, this member function may also throw exceptions to report other situations (such as bad_alloc or system_error).
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
-
<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
-
<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
-
<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
-
<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
-
<unordered_map>C++11
-
<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
-
<atomic>C++11
-
<condition_variable>C++11
-
<future>C++11
-
<mutex>C++11
-
<thread>C++11
-
Other:
- <algorithm>
- <bitset>
-
<chrono>C++11
-
<codecvt>C++11
- <complex>
- <exception>
- <functional>
-
<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
-
<random>C++11
-
<ratio>C++11
-
<regex>C++11
- <stdexcept>
- <string>
-
<system_error>C++11
-
<tuple>C++11
-
<type_traits>C++11
-
<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
<future>
classes
-
futureC++11
-
future_errorC++11
-
packaged_taskC++11
-
promiseC++11
-
shared_futureC++11
-
enum classes
-
future_errcC++11
-
future_statusC++11
-
launchC++11
-
functions
-
asyncC++11
-
future_categoryC++11
-
promise
-
promise::~promiseC++11
-
promise::promiseC++11
member functions
-
promise::get_futureC++11
-
promise::operator=C++11
-
promise::set_exceptionC++11
-
promise::set_exception_at_thread_exitC++11
-
promise::set_valueC++11
-
promise::set_value_at_thread_exitC++11
-
promise::swapC++11
-
non-member overloads
-
swap (promise)C++11
-
non-member specializations
-
uses_allocator<promise>C++11
-
public member function
<future>
std::promise::get_future
future<T> get_future();
Get future
The future object returned can access the value or exception set on the shared state by the promise object once this is ready.
Only one future object can be retrieved for each promise shared state.
After this function has been called, the promise is expected to make its shared state ready at some point (by setting a value or an exception), otherwise it is automatically made ready on destruction containing an exception of type future_error (with a broken_promise error condition).
Parameters
noneReturn value
A future object referring to the same shared state as this promise.T is the type of the value (the template parameter of promise).
Example
|
|
Output
value: 10 |
Data races
The promise object is modified.Exception safety
Basic guarantee: if an exception is thrown, the promise object is in a valid state.This member function throws an exception on the following conditions:
exception type | error condition | description |
---|---|---|
future_error | future_errc::no_state | The object has no shared state (it was moved-from) |
future_error | future_errc::future_already_retrieved | A previous call to this member function already retrieved a future |
See also
- future
- Future (class template)
- promise::set_value
- Set value (public member function)
- promise::set_exception
- Set exception (public member function)
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Spotted an error? contact us