#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
#include <memory>
using std::cout;
using std::vector;
class Has_ptr {
public:
friend void swap(Has_ptr &lhs, Has_ptr &rhs);
friend bool operator<(const Has_ptr &a, const Has_ptr &b);
// constructor
Has_ptr(const std::string &s, int num) : ptr(new std::string(s)), i(num) {}
// copy constructor
Has_ptr(const Has_ptr &a) : ptr(new std::string(*a.ptr)), i(a.i) {}
// copy-assign operator
/*
Has_ptr& operator=(Has_ptr tmp)
{
this->swap(tmp);
return *this;
}
*/
/*
Has_ptr& operator=(Has_ptr &tmp)
{
std::string *x = new std::string(*(tmp.ptr));
delete ptr;
ptr = x;
i = tmp.i;
return *this;
}
*/
// destructor
~Has_ptr() {
delete ptr;
}
void swap(Has_ptr &rhs) {
using std::swap;
swap(ptr, rhs.ptr);
swap(i, rhs.i);
}
void print() {
cout << *ptr << i;
}
private:
std::string *ptr;
int i;
};
// add a swap function
void swap(Has_ptr &lhs, Has_ptr &rhs) {
lhs.swap(rhs);
}
bool operator<(const Has_ptr &a, const Has_ptr &b) {
return a.i < b.i;
}
In C++ Primer 5th,13.3 Swap, exercise 13.31. The question require give the class Has_ptr a < operator and create a vector with few element then sort the vector. The implementation of class is above.
Has_ptr that have 2 data member
- string pointer ptr, point to dynamic memory
- int i
Has_ptr class have following copy-control member
- constructor takes a string and an int.
- copy_constructor, implemented as the class act like value.
- destructor that delete the dynamic memory allocated by ptr.
I have attempt two implementation for the copy-assign operator. One I first create temp string pointer variable x to save the RHS pointer, then delete LHS pointer and finally assign the RHS to LHS. However, this implementation makes the code unable to compiler.
Has_ptr& operator=(Has_ptr &tmp)
{
std::string *x = new std::string(*(tmp.ptr));
delete ptr;
ptr = x;
i = tmp.i;
return *this;
}
The second implementation used copy and swap. This makes code compiler and run fragmentally.
// copy and swap
Has_ptr& operator=(Has_ptr tmp)
{
this->swap(tmp);
return *this;
}
My main function is the following
int main() {
Has_ptr a("a", 0), b("b", 1), c("c", 2);
a.print();
vector<Has_ptr> coll{a, b, c};
std::sort(coll.begin(), coll.end());
for (auto h : coll)
h.print();
}
The second implementation produce no error/warning message while compiler and produce following output
a0a0
The first implementation produce following error message
In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\algorithm:62:0,
from 13_31.c++:9:
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h: In instantiation of 'void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]':
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1882:25: required from 'void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1968:31: required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:4707:18: required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >]'
13_31.c++:88:39: required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1849:17: error: invalid initialization of non-const reference of type 'Has_ptr&' from an rvalue of type 'std::remove_reference<Has_ptr&>::type {aka Has_ptr}'
*__first = _GLIBCXX_MOVE(__val);
^
13_31.c++:42:14: note: initializing argument 1 of 'Has_ptr& Has_ptr::operator=(Has_ptr&)'
Has_ptr& operator=(Has_ptr &tmp)
^~~~~~~~
In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:61:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\algorithm:62,
from 13_31.c++:9:
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h: In instantiation of 'void std::__pop_heap(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]':
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1672:19: required from 'void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1930:25: required from 'void std::__partial_sort(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1945:27: required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Size = int; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1965:25: required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:4707:18: required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >]'
13_31.c++:88:39: required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h:246:17: error: invalid initialization of non-const reference of type 'Has_ptr&' from an rvalue of type 'std::remove_reference<Has_ptr&>::type {aka Has_ptr}'
*__result = _GLIBCXX_MOVE(*__first);
^
13_31.c++:42:14: note: initializing argument 1 of 'Has_ptr& Has_ptr::operator=(Has_ptr&)'
Has_ptr& operator=(Has_ptr &tmp)
^~~~~~~~
In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:61:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\algorithm:62,
from 13_31.c++:9:
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h: In instantiation of 'void std::__adjust_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Distance = int; _Tp = Has_ptr; _Compare = __gnu_cxx::__ops::_Iter_less_iter]':
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h:335:22: required from 'void std::__make_heap(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1669:23: required from 'void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1930:25: required from 'void std::__partial_sort(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1945:27: required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Size = int; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1965:25: required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:4707:18: required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >]'
13_31.c++:88:39: required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h:220:29: error: invalid initialization of non-const reference of type 'Has_ptr&' from an rvalue of type 'std::remove_reference<Has_ptr&>::type {aka Has_ptr}'
*(__first + __holeIndex) = _GLIBCXX_MOVE(*(__first + __secondChild));
^
13_31.c++:42:14: note: initializing argument 1 of 'Has_ptr& Has_ptr::operator=(Has_ptr&)'
Has_ptr& operator=(Has_ptr &tmp)
^~~~~~~~
In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:61:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\algorithm:62,
from 13_31.c++:9:
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_heap.h:226:29: error: invalid initialization of non-const reference of type 'Has_ptr&' from an rvalue of type 'std::remove_reference<Has_ptr&>::type {aka Has_ptr}'
*(__first + __holeIndex) = _GLIBCXX_MOVE(*(__first
^
13_31.c++:42:14: note: initializing argument 1 of 'Has_ptr& Has_ptr::operator=(Has_ptr&)'
Has_ptr& operator=(Has_ptr &tmp)
^~~~~~~~
In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\char_traits.h:39:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ios:40,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ostream:38,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\iostream:39,
from 13_31.c++:6:
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algobase.h: In instantiation of 'static _BI2 std::__copy_move_backward<true, false, std::random_access_iterator_tag>::__copy_move_b(_BI1, _BI1, _BI2) [with _BI1 = Has_ptr*; _BI2 = Has_ptr*]':
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algobase.h:588:58: required from '_BI2 std::__copy_move_backward_a(_BI1, _BI1, _BI2) [with bool _IsMove = true; _BI1 = Has_ptr*; _BI2 = Has_ptr*]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algobase.h:598:5: required from '_BI2 std::__copy_move_backward_a2(_BI1, _BI1, _BI2) [with bool _IsMove = true; _BI1 = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _BI2 = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algobase.h:668:48: required from '_BI2 std::move_backward(_BI1, _BI1, _BI2) [with _BI1 = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _BI2 = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1848:8: required from 'void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1882:25: required from 'void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:1968:31: required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algo.h:4707:18: required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Has_ptr*, std::vector<Has_ptr> >]'
13_31.c++:88:39: required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\stl_algobase.h:548:18: error: invalid initialization of non-const reference of type 'Has_ptr&' from an rvalue of type 'std::remove_reference<Has_ptr&>::type {aka Has_ptr}'
*--__result = std::move(*--__last);
~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
13_31.c++:42:14: note: initializing argument 1 of 'Has_ptr& Has_ptr::operator=(Has_ptr&)'
Has_ptr& operator=(Has_ptr &tmp)
^~~~~~~~