Can someone help correct my understanding std::move?
I thought that if a reference to an r-value is out of scope, then it is referenced if it was assigned using an operator std::move. Why is this not the case in the code below?
#include<iostream>
using namespace std;
int main()
{
string one = "1 - one";
string two = "2 - two";
{
string & lValRef = one;
string && rValRef = std::move(two);
string newS(rValRef);
}
cout << "one : " << one << endl;
cout << "two : " << two << endl;
{
string temp(std::move(one));
string tempAssignment;
tempAssignment = std::move(two);
}
cout << "one : " << one << endl;
cout << "two : " << two << endl;
return 0;
}
You can play with him here .
I always thought that using std::moveis a way to leave objects in a “deleted state”. Therefore, I was surprised that the "two" printed something for the first time. Is it used to create && r-value, as I did ('rValRef')? [I understand that a std::move()will be required around my "rValRef" for it to work as desired].
, , . , , :) .
#include <iostream>
#include <vector>
using namespace std;
class SimpleClass {
friend ostream& operator<<(ostream & s,const SimpleClass & rhs);
private:
vector<char> data;
public:
SimpleClass(initializer_list<char> lst):data(lst.size()) {
copy(lst.begin(),lst.end(),data.begin());
}
SimpleClass(size_t dim = 0):data(dim){};
virtual ~SimpleClass() = default;
SimpleClass(const SimpleClass & rhs) = default;
SimpleClass & operator=(const SimpleClass & rhs) = default;
SimpleClass(SimpleClass && rhs):data(move(rhs.data)){};
SimpleClass & operator=(SimpleClass && rhs){
if (this != &rhs){
this->data = move(rhs.data);
return *this;
}
}
};
ostream& operator<<(ostream & s,const SimpleClass & rhs){
for (size_t i = 0; i != rhs.data.size(); ++i)
s << rhs.data[i];
return s;
}
int main()
{
SimpleClass one = {'o','n','e'};
SimpleClass two = {'t','w','o'};
{
SimpleClass & lValRef = one;
SimpleClass && rValRef = std::move(two);
}
cout << "one : " << one << endl;
cout << "two : " << two << endl;
{
SimpleClass temp(std::move(one));
SimpleClass tempAssignment;
tempAssignment = std::move(two);
}
cout << "one : " << one << endl;
cout << "two : " << two << endl;
return 0;
}