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Returns whether the future object is currently associated with a shared state.
For default-constructed future objects, this function returns false (unless move-assigned a valid future).
Futures can only be initially constructed with valid shared states by certain provider functions, such as async, promise::get_future or packaged_task::get_future.
Once the value of the shared state is retrieved with future::get, calling this function returns
Output:
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
-
future
-
future::~futureC++11
-
future::futureC++11
member functions
-
future::getC++11
-
future::operator=C++11
-
future::shareC++11
-
future::validC++11
-
future::waitC++11
-
future::wait_forC++11
-
future::wait_untilC++11
-
public member function
<future>
std::future::valid
bool valid() const noexcept;
Check for valid shared state
For default-constructed future objects, this function returns false (unless move-assigned a valid future).
Futures can only be initially constructed with valid shared states by certain provider functions, such as async, promise::get_future or packaged_task::get_future.
Once the value of the shared state is retrieved with future::get, calling this function returns
false (unless move-assigned a new valid future).Parameters
noneReturn value
true if the object is associated with a shared state.false otherwise.Example
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Output:
foo is not valid bar's value: 10 |
Data races
The future object is accessed.Exception safety
No-throw guarantee: never throws exceptions.See also
- future::get
- Get value (public member function)
- future::wait
- Wait for ready (public member function)
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Spotted an error? contact us