Exception propagation and std::future

Question

My understanding is that when an asynchronous operation throws an exception, it will be propagated back to a thread that calls std::future::get(). However, when su

Answer 1

vs2012\vc11\crt\future.cpp

there is an error with the

static const char *const _Future_messages[] =
{   // messages for future errors
"broken promise",
"future already retrieved",
"promise already satisfied",
"no state"
};

this code generated an invalid acceso to "_Future_messages" because _Mycode.value() return 4.

    const char *__CLR_OR_THIS_CALL what() const _THROW0()
    {   // get message string
    return (_Get_future_error_what(_Mycode.value()));
    }

// code example

    std::future<int> empty;
try {
    int n = empty.get();
} catch (const std::future_error& e) {
   const error_code eCode = e.code();
   char *sValue = (char*)e.what();
   std::cout << "Caught a future_error with code " << eCode.message()
              << " - what" << sValue << endl;
}

Answer 2

It is ignored and discarded, just like if you wait() for a value but never get() it.

wait() simply says "block until the future is ready", be that ready with a value or exception. It's up to the caller to actually get() the value (or exception). Usually you'll just use get(), which waits anyway.