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#include <iostream>
#include <string>
using namespace std;
 
int main() {
 
	std::string s1("s1");
	std::string s2("s2");
 
	//std::swap(s1, s2);
	std::swap(s1, std::string());
 
	// your code goes here
	return 0;
}

prog.cpp: In function ‘int main()’:
prog.cpp:11:29: error: no matching function for call to ‘swap(std::__cxx11::string&, std::__cxx11::string)’
  std::swap(s1, std::string());
                             ^
In file included from /usr/include/c++/6/bits/nested_exception.h:40:0,
                 from /usr/include/c++/6/exception:173,
                 from /usr/include/c++/6/ios:39,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/6/bits/move.h:179:5: note: candidate: typename std::enable_if<std::__and_<std::is_move_constructible<_Tp>, std::is_move_assignable<_Tp> >::value>::type std::swap(_Tp&, _Tp&) [with _Tp = std::__cxx11::basic_string<char>; typename std::enable_if<std::__and_<std::is_move_constructible<_Tp>, std::is_move_assignable<_Tp> >::value>::type = void] <near match>
     swap(_Tp& __a, _Tp& __b)
     ^~~~
/usr/include/c++/6/bits/move.h:179:5: note:   conversion of argument 2 would be ill-formed:
prog.cpp:11:21: error: invalid initialization of non-const reference of type ‘std::__cxx11::basic_string<char>&’ from an rvalue of type ‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’
  std::swap(s1, std::string());
                     ^~~~~~~~
In file included from /usr/include/c++/6/bits/nested_exception.h:40:0,
                 from /usr/include/c++/6/exception:173,
                 from /usr/include/c++/6/ios:39,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/6/bits/move.h:202:5: note: candidate: template<class _Tp, long unsigned int _Nm> typename std::enable_if<std::__is_swappable<_Tp>::value>::type std::swap(_Tp (&)[_Nm], _Tp (&)[_Nm])
     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
     ^~~~
/usr/include/c++/6/bits/move.h:202:5: note:   template argument deduction/substitution failed:
prog.cpp:11:29: note:   mismatched types ‘_Tp [_Nm]’ and ‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’
  std::swap(s1, std::string());
                             ^
In file included from /usr/include/c++/6/bits/stl_algobase.h:64:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/6/bits/stl_pair.h:471:5: note: candidate: template<class _T1, class _T2> void std::swap(std::pair<_T1, _T2>&, std::pair<_T1, _T2>&)
     swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
     ^~~~
/usr/include/c++/6/bits/stl_pair.h:471:5: note:   template argument deduction/substitution failed:
prog.cpp:11:29: note:   ‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’ is not derived from ‘std::pair<_T1, _T2>’
  std::swap(s1, std::string());
                             ^
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/6/bits/basic_string.h:5302:5: note: candidate: void std::swap(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>] <near match>
     swap(basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^~~~
/usr/include/c++/6/bits/basic_string.h:5302:5: note:   conversion of argument 2 would be ill-formed:
prog.cpp:11:21: error: invalid initialization of non-const reference of type ‘std::__cxx11::basic_string<char>&’ from an rvalue of type ‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’
  std::swap(s1, std::string());
                     ^~~~~~~~

Standard output is empty