C++ Brain Teasers: Exercise Your Mind/

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Discussion: Moving Out

Discussion: Moving Out

Execute the code to understand the output and gain insights into the behavior of moved-from objects.

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Run the code

Now, it’s time to execute the code and observe the output.

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#include <iostream>
#include <string>
int main()
{
    std::string hello{"Hello, World!"};
    std::string other(std::move(hello));
    std::cout << "'" << hello << "'";
}

Understanding the output

A moved-from object should no longer be used, as resources will have been moved out of it, pointers might point to destroyed objects, and so on.

How a particular moved-from object behaves is up to the implementer of that class. The implementer has a lot of freedom here, but at a minimum, the object should be safe to destroy so nothing breaks when, for instance, a moved-from local variable goes out of scope. Unless explicitly documented, we, as a user, should not assume that a class makes any further guarantees.

Standard library guarantee

The C++ standard provides an additional guarantee for the classes in the standard library, though:

Objects of types defined in the C++ standard library may be moved ...