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# std::promise::set_exception

From cppreference.com
< cpp‎ | thread‎ | promise

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

Stores the exception pointer `p` into the shared state and makes the state ready.

The operation is atomic, i.e. it behaves as though they 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.

### [edit] Parameters

p | - | exception pointer to store

### [edit] Return value

(none)

### [edit] Exceptions

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`.

### [edit] Example

Run this code

    #include <thread>
    #include <iostream>
    #include <future>

    int main()
    {
        std::promise<int> result;

        std::thread t([&]{
                try {
                    // code that may throw
                    throw std::runtime_error("Example");
                } catch(...) {
                    try {
                        // store anything thrown in the promise
                        result.set_exception(std::current_exception());
                    } catch(...) {} // set_exception() may throw too
                }
        });

        try {
            std::cout << result.get_future().get();
        } catch(const std::exception& e) {
            std::cout << "Exception from the thread: " << e.what() << '\n';
        }
        t.join();
    }

Output:

    Exception from the thread: Example

### [edit] See also

set_exception_at_thread_exit | sets the result to indicate an exception while delivering the notification only at thread exit (public member function) [edit]

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