accessing optional by de-refence pointer

Eclipse CDT optional is in <experimental\optional> and IDE red squiggly line need to be ignored

p default to either false or default value like 0
*p =default 0 or *p=assigned value if has a value like 90

#include <iostream>
#include <vector>
#include <cstdlib>
#include <experimental\optional>

using namespace std;

int main() {

 std::experimental::optional<int> p;

        cout<<*p<<endl;
 if(!p)
  cout<<"not set"<<endl;

 if(p<=12)
  cout<<"compare to int p=0"<<endl;

 p=90;
 if(p)
 {
  cout<<"access value by* "<<*p<<endl;
 }

 return 0;
}