// forward_list::before_begin
#include <iostream>
#include <forward_list>
int main ()
{
std::forward_list<int> mylist = {20, 30, 40, 50};
mylist.insert_after ( mylist.begin(), 11 ); //mylist contains: 20 11 30 40 50
mylist.insert_after ( mylist.before_begin(), 11 ); //mylist contains: 11 20 30 40 50
std::cout << "mylist contains:";
for ( int& x: mylist ) std::cout << ' ' << x;
std::cout << '\n';
return 0;
}
mylist.begin()
mylist.before_begin()
指向位置不同before_begin(),在begin() 之前