Passing a reference to a C++ constructor -

Passing a reference to a C++ constructor -

i have this code:

#include <iostream> using namespace std; struct x { int = 1; }; struct y { x &_x; y(x &x) : _x(x) {} }; // intentionally typoed version of y, without reference in constructor struct z { x &_x; z(x x) : _x(x) {} }; int main() { x x; y y(x); z z(x); cout << "x: " << &x << endl; cout << "y.x: " << &y._x << endl; cout << "z.x: " << &z._x << endl; }

i maintain finding myself forgetting & in constructor of classes of format.

this outputs following:

x: 0xbfa195f8 y.x: 0xbfa195f8 z.x: 0xbfa195fc

why behaviour different in case of y , z?

and why not error initialize x &_x fellow member instance of type x in constructor of y?

a re-create of object created when constructor called, hence different output z.x. lifespan of object limited - exists in constructor. undefined behavior , reference come invalid.

to prevent such behavior in applications practice mark re-create constructor , assignment operator private.

c++ reference