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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 packaged_task once its stored task is called.
Only one future object can be retrieved for each packaged_task shared state.
After this function has been called, the packaged_task is expected to make its shared state ready at some point (by calling its stored task), otherwise it is automatically made ready on destruction containing an exception of type future_error (with a broken_promise error condition).
Ret is the return type of the stored task (the first template parameter of packaged_task).
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
-
packaged_task
-
packaged_task::~packaged_taskC++11
-
packaged_task::packaged_taskC++11
member functions
-
packaged_task::get_futureC++11
-
packaged_task::make_ready_at_thread_exitC++11
-
packaged_task::operator()C++11
-
packaged_task::operator=C++11
-
packaged_task::resetC++11
-
packaged_task::swapC++11
-
packaged_task::validC++11
-
non-member overloads
-
swap (packaged_task)C++11
-
non-member specializations
- Reference
- <future>
- packaged_task
- get_future
public member function
<future>
std::packaged_task::get_future
future<Ret> get_future();
Get future
The future object returned can access the value or exception set on the shared state by the packaged_task once its stored task is called.
Only one future object can be retrieved for each packaged_task shared state.
After this function has been called, the packaged_task is expected to make its shared state ready at some point (by calling its stored task), 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 packaged_task.Ret is the return type of the stored task (the first template parameter of packaged_task).
Example
|
|
Output:
The triple of 33 is 99. |
Data races
The packaged_task object is modified.Exception safety
Basic guarantee: if an exception is thrown, the packaged_task 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 |
| future_error | future_errc::future_already_retrieved | A previous call to this member function already retrieved a future |
See also
- future
- Future (class template)
- packaged_task::operator()
- Call stored task (public member function)
- packaged_task::valid
- Check for valid shared state (public member function)
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Spotted an error? contact us