string s = "á";
if(s == 'á')
cout << "\nok";
el error:
a.cc:14:11: warning: multi-character character constant [-Wmultichar]
if(s == 'á')
^
a.cc: In function ‘int main()’:
a.cc:14:8: error: no match for ‘operator==’ (operand types are ‘std::string {aka std::basic_string<char>}’ and ‘int’)
if(s == 'á')
^
a.cc:14:8: note: candidates are:
In file included from /usr/include/c++/4.8/iosfwd:40:0,
from /usr/include/c++/4.8/ios:38,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/postypes.h:216:5: note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)
operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
^
/usr/include/c++/4.8/bits/postypes.h:216:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const std::fpos<_StateT>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/bits/stl_algobase.h:64:0,
from /usr/include/c++/4.8/bits/char_traits.h:39,
from /usr/include/c++/4.8/ios:40,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/stl_pair.h:214:5: note: template<class _T1, class _T2> bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
^
/usr/include/c++/4.8/bits/stl_pair.h:214:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const std::pair<_T1, _T2>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/bits/stl_algobase.h:67:0,
from /usr/include/c++/4.8/bits/char_traits.h:39,
from /usr/include/c++/4.8/ios:40,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/stl_iterator.h:291:5: note: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
operator==(const reverse_iterator<_Iterator>& __x,
^
/usr/include/c++/4.8/bits/stl_iterator.h:291:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const std::reverse_iterator<_Iterator>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/bits/stl_algobase.h:67:0,
from /usr/include/c++/4.8/bits/char_traits.h:39,
from /usr/include/c++/4.8/ios:40,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/stl_iterator.h:341:5: note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
operator==(const reverse_iterator<_IteratorL>& __x,
^
/usr/include/c++/4.8/bits/stl_iterator.h:341:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const std::reverse_iterator<_Iterator>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/string:41:0,
from /usr/include/c++/4.8/bits/locale_classes.h:40,
from /usr/include/c++/4.8/bits/ios_base.h:41,
from /usr/include/c++/4.8/ios:42,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/allocator.h:128:5: note: template<class _T1, class _T2> bool std::operator==(const std::allocator<_CharT>&, const std::allocator<_T2>&)
operator==(const allocator<_T1>&, const allocator<_T2>&)
^
/usr/include/c++/4.8/bits/allocator.h:128:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const std::allocator<_CharT>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/string:41:0,
from /usr/include/c++/4.8/bits/locale_classes.h:40,
from /usr/include/c++/4.8/bits/ios_base.h:41,
from /usr/include/c++/4.8/ios:42,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/allocator.h:133:5: note: template<class _Tp> bool std::operator==(const std::allocator<_CharT>&, const std::allocator<_CharT>&)
operator==(const allocator<_Tp>&, const allocator<_Tp>&)
^
/usr/include/c++/4.8/bits/allocator.h:133:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const std::allocator<_CharT>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/string:52:0,
from /usr/include/c++/4.8/bits/locale_classes.h:40,
from /usr/include/c++/4.8/bits/ios_base.h:41,
from /usr/include/c++/4.8/ios:42,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/basic_string.h:2486:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
^
/usr/include/c++/4.8/bits/basic_string.h:2486:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: mismatched types ‘const std::basic_string<_CharT, _Traits, _Alloc>’ and ‘int’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/string:52:0,
from /usr/include/c++/4.8/bits/locale_classes.h:40,
from /usr/include/c++/4.8/bits/ios_base.h:41,
from /usr/include/c++/4.8/ios:42,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/basic_string.h:2493:5: note: template<class _CharT> typename __gnu_cxx::__enable_if<std::__is_char<_Tp>::__value, bool>::__type std::operator==(const std::basic_string<_CharT>&, const std::basic_string<_CharT>&)
operator==(const basic_string<_CharT>& __lhs,
^
/usr/include/c++/4.8/bits/basic_string.h:2493:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: mismatched types ‘const std::basic_string<_CharT>’ and ‘int’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/string:52:0,
from /usr/include/c++/4.8/bits/locale_classes.h:40,
from /usr/include/c++/4.8/bits/ios_base.h:41,
from /usr/include/c++/4.8/ios:42,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/basic_string.h:2507:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
operator==(const _CharT* __lhs,
^
/usr/include/c++/4.8/bits/basic_string.h:2507:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: mismatched types ‘const _CharT*’ and ‘std::basic_string<char>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/string:52:0,
from /usr/include/c++/4.8/bits/locale_classes.h:40,
from /usr/include/c++/4.8/bits/ios_base.h:41,
from /usr/include/c++/4.8/ios:42,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/basic_string.h:2519:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
^
/usr/include/c++/4.8/bits/basic_string.h:2519:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: mismatched types ‘const _CharT*’ and ‘int’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/bits/locale_facets.h:48:0,
from /usr/include/c++/4.8/bits/basic_ios.h:37,
from /usr/include/c++/4.8/ios:44,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/streambuf_iterator.h:204:5: note: template<class _CharT, class _Traits> bool std::operator==(const std::istreambuf_iterator<_CharT, _Traits>&, const std::istreambuf_iterator<_CharT, _Traits>&)
operator==(const istreambuf_iterator<_CharT, _Traits>& __a,
^
/usr/include/c++/4.8/bits/streambuf_iterator.h:204:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const std::istreambuf_iterator<_CharT, _Traits>’
if(s == 'á')
^
In file included from /usr/include/x86_64-linux-gnu/c++/4.8/bits/c++allocator.h:33:0,
from /usr/include/c++/4.8/bits/allocator.h:46,
from /usr/include/c++/4.8/string:41,
from /usr/include/c++/4.8/bits/locale_classes.h:40,
from /usr/include/c++/4.8/bits/ios_base.h:41,
from /usr/include/c++/4.8/ios:42,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/ext/new_allocator.h:139:5: note: template<class _Tp> bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator<_Tp>&, const __gnu_cxx::new_allocator<_Tp>&)
operator==(const new_allocator<_Tp>&, const new_allocator<_Tp>&)
^
/usr/include/c++/4.8/ext/new_allocator.h:139:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const __gnu_cxx::new_allocator<_Tp>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/bits/stl_algobase.h:67:0,
from /usr/include/c++/4.8/bits/char_traits.h:39,
from /usr/include/c++/4.8/ios:40,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/stl_iterator.h:811:5: note: template<class _Iterator, class _Container> bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator<_Iterator, _Container>&, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)
operator==(const __normal_iterator<_Iterator, _Container>& __lhs,
^
/usr/include/c++/4.8/bits/stl_iterator.h:811:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const __gnu_cxx::__normal_iterator<_Iterator, _Container>’
if(s == 'á')
^
In file included from /usr/include/c++/4.8/bits/stl_algobase.h:67:0,
from /usr/include/c++/4.8/bits/char_traits.h:39,
from /usr/include/c++/4.8/ios:40,
from /usr/include/c++/4.8/ostream:38,
from /usr/include/c++/4.8/iostream:39,
from a.cc:1:
/usr/include/c++/4.8/bits/stl_iterator.h:805:5: note: template<class _IteratorL, class _IteratorR, class _Container> bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator<_IteratorL, _Container>&, const __gnu_cxx::__normal_iterator<_IteratorR, _Container>&)
operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
^
/usr/include/c++/4.8/bits/stl_iterator.h:805:5: note: template argument deduction/substitution failed:
a.cc:14:11: note: ‘std::string {aka std::basic_string<char>}’ is not derived from ‘const __gnu_cxx::__normal_iterator<_IteratorL, _Container>’
if(s == 'á')