一道c++笔试题

1 #include <vector> 
2 
3 struct Point
 { 4     Point(int xx, int yy) 
5         : x(xx) 6         , y(yy) 7    
 {} 
8 
9     int const x;
10     int const y;
11 };
12
13 int main()
14 {
15     std::vector<Point> pts;
16     pts.push_back(Point(0, 0));
17     return 0;
18 }

编译出现下列错误：

14.cpp: 在成员函数‘Point& Point::operator=(const Point&)’中:
14.cpp:4:8：自‘void std::vector<_Tp, _Alloc>::_M_insert_aux(std::vector<_Tp, _Alloc>::iterator, const _Tp&) [with _Tp = Point, _Alloc = std::allocator<Point>, std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<Point*, std::vector<Point> >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer = Point*]’实例化
/usr/include/c++/4.6/bits/stl_vector.h:834:4：自‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = Point, _Alloc = std::allocator<Point>, std::vector<_Tp, _Alloc>::value_type = Point]’实例化
14.cpp:13:26：从此处实例化
14.cpp:4:8: 错误： non-static const member ‘const int Point::x’, can’t use default assignment operator
14.cpp:4:8: 错误： non-static const member ‘const int Point::y’, can’t use default assignment operator
In file included from /usr/include/c++/4.6/vector:70:0,
                 from 14.cpp:2:
/usr/include/c++/4.6/bits/vector.tcc: 在成员函数‘void std::vector<_Tp, _Alloc>::_M_insert_aux(std::vector<_Tp, _Alloc>::iterator, const _Tp&) [with _Tp = Point, _Alloc = std::allocator<Point>, std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<Point*, std::vector<Point> >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer = Point*]’中:
/usr/include/c++/4.6/bits/vector.tcc:314:4: 附注： 在这里第一次需要生成的方法‘Point& Point::operator=(const Point&)’

原因分析：

由于模板必须支持复制操作，但const限定的变量一旦绑定是不能够修改的