&&运算符与std :: string的用法是什么

Question

I would like to better understand the use of the operator && in the example below with std::string

Code:

#include <iostream>
using namespace std;

const std::string GetEditTxtAccount()
{
 std::string str = "Hello";
 return str;
}

int main()
{
   const string&& x = GetEditTxtAccount();
               ^^^
}

so why did we used the operator && in the main?

Thank you.

Answer 1

This code is storing an rvalue reference to the new string, relying on lifetime extension to keep the actual string alive.

In this case it's pretty much like doing const string& x = GetEditTxtAccount() , which is also pointless.

It's also arguably dangerous because if the function returned a reference then you'd potentially have it dangling.

Certainly there is no benefit in doing this.

Just declare a proper value instead:

const string x = GetEditTxtAccount();

If you're worried about copies, you won't get one, because of move semantics (pre-C++17) and because of guaranteed elision (since C++17).

As for why the author wrote it this way, well, some people go over the top with rvalue refs without really understanding why.