c++ - Pushing into a vector of struct an element of that vector -

i've declared struct this:

struct point{     double x,y;     point(){}     point(double xx,double yy): x(xx),y(yy){} }; 

and i'm trying fill vector this:

vector<point> s(1); point tmp(1,2); s[0]=tmp; s.push_back(s[0]); 

unfortunately, doing gives me wrong answer when display content of s[1], s.push_back((point)s[0]) leads expected answer (e.g. copy of s[0]).

what difference between s.push_back(s[0]) , s.push_back((point)s[0]) explains differennce ?

is there auto type conversion or going under hood?

push_back take argument const reference (and other overload rvalue reference), so

s.push_back(s[0]); 

uses lvalue-reference of first element, but, push_back may reallocate if capacity not large enough. , reference pulled s[0] left dangling, , no longer viable.

on other side

s.push_back((point)s[0]); 

create temporary, , s[0] no longer used, allowing push valid point in vector.