c++ - When copy constructor or assignment constructor is called? -

triny quiz web , see code. result prints 02

which means default copy constructor used list initialization while assignment constructor used vector. why?

#include <algorithm> #include <iostream> #include <list> #include <vector>  class int { public:     int(int = 0) : m_i(i) { }  public:     bool operator<(const int& a) const { return this->m_i < a.m_i; }      int& operator=(const int &a)     {         this->m_i = a.m_i;         ++m_assignments;         return *this;     }      static int get_assignments() { return m_assignments; }  private:     int m_i;     static int m_assignments; };  int int::m_assignments = 0;  int main() {     std::list<int> l({ int(3), int(1) });     l.sort();     std::cout << (int::get_assignments() > 0 ? 1 : 0);      std::vector<int> v({ int(2), int() });     std::sort(v.begin(), v.end());     std::cout << (int::get_assignments() > 0 ? 2 : 0) << std::endl;      return 0; } 

which means default copy constructor used list initialization while assignment constructor used vector

if remove std::sort(v.begin(), v.end()); instruction program prints 00. assignment operator used sorting.

note: list can sorted modifying pointers (so l.sort() doesn't require operator=).