When move constructor will get called in C++11? - c++11

Question

I am not able to understand why why move constructor is not getting called while move assignment is able to while if I use move function in Line X , it used to call the move constructor . Can anybody tell what will be the way or syntax to call the move constructor .
#include <iostream>
#include <cstring>
#include <algorithm>
#include <memory>
using namespace std;
class String
{
char *s;
int len;
public:
String():s(nullptr),len(0){ cout<<"Default "; }
String(char *p)
{
if(p)
{
len = strlen(p);
s = new char[len];
strcpy(s,p);
}
else
{
s = nullptr;
len = 0;
}
cout<<"Raw ";
}
String(String &p)
{
if(p.s)
{
len = strlen(p.s);
s = new char[len];
strcpy(s,p.s);
}
else
{
s = nullptr;
len = 0;
}
cout<<"Copy ";
}
String & operator = (const String & p)
{
if(this != &p)
{
delete []s;
s = nullptr;
len = 0;
if(p.len)
{
len = p.len;
s = new char[len];
strcpy(s,p.s);
}
}
cout<<"Assignment ";
return *this;
}
String( String && p):s(nullptr),len(0) // move constructor
{
len = p.len;
s = p.s;
p.s = nullptr;
p.len = 0;
cout<<"Move Copy ";
}
String & operator = (String && p) // move assignment
{
if(this != &p)
{
delete []s;
len = 0;
s = nullptr;
if(p.len)
{
len = p.len;
s = p.s;
p.s = nullptr;
p.len = 0;
}
}
cout<<"Move Assignment ";
return *this;
}
~String() { delete []s; cout<<"Destructor \n"; }
void show() { cout<<s<<endl; }
};
int main()
{
String s1("Something ");
String s2(s1);
s1.show();
s2.show();
String s4(String("Nothing ")); // Line X
s4.show();
String s5;
s5 = String(s2);
s5.show();
return 0;
}
OUTPUT:
Raw Copy Something
Something
Raw Nothing
Default Copy Move Assignment Destructor
Something
Destructor
Destructor
Destructor
Destructor

Answer 1

It's the second variant of the copy elision explained here: http://en.cppreference.com/w/cpp/language/copy_elision.
http://coliru.stacked-crooked.com/a/17f811a0be4ecba3
Note -fno-elide-constructors, it disables the optimization in g++.
Output:
Copy Something
Something
Raw Move Copy Move Copy Destructor
Destructor
Nothing
Default Copy Move Assignment Destructor
Something
Destructor
Destructor
Destructor
Destructor