std::promise::set_value
STD：：承诺：：设定[医]价值
| void set_value( const R& value | (1) | (member only of generic promise template)(since C++11) |
|---|---|---|
| void set_value( R&& value | (2) | (member only of generic promise template)(since C++11) |
| void set_value( R& value | (3) | (member only of promise<R&> template specialization)(since C++11) |
| void set_value( | (4) | (member only of promise<void> template specialization)(since C++11) |
原子存储value进入共享状态并使状态就绪。
这个操作的行为就像set_value，，，set_exception，，，set_value_at_thread_exit，和set_exception_at_thread_exit在更新允诺对象时获取与承诺对象关联的单个互斥对象。
如果没有共享状态，或者共享状态已经存储了值或异常，则引发异常。
参数
| value | - | value to store in the shared state |
|---|
返回值
%280%29
例外
std::future_error在下列条件下：
*this没有共享状态。错误类别设置为no_state...
- 共享状态已存储值或异常。错误类别设置为
promise_already_satisfied...
此外：
的副本构造函数引发的任何异常。value
2%29移动构造函数引发的任何异常。value
例
这个例子显示了如何promise<void>可用作线程之间的信号。
二次
#include <thread>
#include <future>
#include <cctype>
#include <vector>
#include <algorithm>
#include <iterator>
#include <iostream>
#include <sstream>
int main()
{
std::istringstream iss_numbers{"3 4 1 42 23 -23 93 2 -289 93"};
std::istringstream iss_letters{" a 23 b,e a2 k k?a;si,ksa c"};
std::vector<int> numbers;
std::vector<char> letters;
std::promise<void> numbers_promise, letters_promise;
auto numbers_ready = numbers_promise.get_future(
auto letter_ready = letters_promise.get_future(
std::thread value_reader([&]
{
// I/O operations.
std::copy(std::istream_iterator<int>{iss_numbers},
std::istream_iterator<int>{},
std::back_inserter(numbers)
//Notify for numbers.
numbers_promise.set_value(
std::copy_if(std::istreambuf_iterator<char>{iss_letters},
std::istreambuf_iterator<char>{},
std::back_inserter(letters),
::isalpha
//Notify for letters.
letters_promise.set_value(
}
numbers_ready.wait(
std::sort(numbers.begin(), numbers.end()
if (letter_ready.wait_for(std::chrono::seconds(1)) ==
std::future_status::timeout)
{
//output the numbers while letters are being obtained.
for (int num : numbers) std::cout << num << ' ';
numbers.clear( //Numbers were already printed.
}
letter_ready.wait(
std::sort(letters.begin(), letters.end()
//If numbers were already printed, it does nothing.
for (int num : numbers) std::cout << num << ' ';
std::cout << '\n';
for (char let : letters) std::cout << let << ' ';
std::cout << '\n';
value_reader.join(
}
二次
产出：
二次
-289 -23 1 2 3 4 23 42 93 93
a a a a b c e i k k k s s
二次
另见
| set_exception | sets the result to indicate an exception (public member function) |
|---|
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