void set_exception( std::exception_ptr p );
(since C++11)

Atomically stores the exception pointer p into the shared state and makes the state ready.

The operation behaves as though set_value, set_exception, set_value_at_thread_exit, and set_exception_at_thread_exit acquire a single mutex associated with the promise object while updating the promise object.

An exception is thrown if there is no shared state or the shared state already stores a value or exception.


p - exception pointer to store. The behavior is undefined if p is null.

Return value



std::future_error on the following conditions:

  • *this has no shared state. The error category is set to no_state.
  • The shared state already stores a value or exception. The error category is set to promise_already_satisfied.


#include <thread>
#include <iostream>
#include <future>
int main()
    std::promise<int> p;
    std::future<int> f = p.get_future();
    std::thread t([&p]{
        try {
            // code that may throw
            throw std::runtime_error("Example");
        } catch(...) {
            try {
                // store anything thrown in the promise
            } catch(...) {} // set_exception() may throw too
    try {
        std::cout << f.get();
    } catch(const std::exception& e) {
        std::cout << "Exception from the thread: " << e.what() << '\n';


Exception from the thread: Example

See also

sets the result to indicate an exception while delivering the notification only at thread exit
(public member function)

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