C ++ Lambda捕获搞乱局部变量值

Question

I am not sure whether this is a VS 2010 problem or I am misunderstanding something completely. I am creating a boost thread via a lambda function which needs to modify a local variable:

    auto oCurrTime( boost::posix_time::microsec_clock::universal_time() );
    auto spRequestSequenceThread = make_unique<boost::thread>( [&oCurrTime, this]()
    {
        while ( !checkAgainstSpecificTime(oCurrTime) )
        {
            ...
        }
        :
        :
    }

Before creating the thread, oCurrTime is something like 2864273654234872634, but within the thread this value gets lost and oCurrTime immediately is something like 487465847564875465, rendering the while loop (where a time difference to some specific Time is evaluated) useless.

Thanks a lot for help.

PS: The above code is part of a function of a class

Answer 1

It look like you execute your thread from class method - you provide this in lambda capture list. This also means oCurrTime is local variable, so if you capture it by reference : you use & , then when your thread executes oCurrTime will be removed from stack because scope when it was defined already ended.

The solution is to pass oCurrTime by value (remove & ) if it is possible, or join your thread before your method ends - also if that is possible. You could also make oCurrTime a class variable.

Answer 2

As you're capturing it by reference [&oCurrTime]
If oCurrTime goes out of scope you will have a dangling reference .

One solution could be to capture by value.