16.3如果sales_data没有定义运算符，那么给出如下错误：
sales_data.cc: In instantiation of ‘int compare(const T&, const T&) [with T = Sales_data]’:
sales_data.cc:143:22: required from here
sales_data.cc:90:6: error: no match for ‘operator<’ (operand types are ‘const Sales_data’ and ‘const Sales_data’)
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:64,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_pair.h:454:5: note: candidate: ‘template<class _T1, class _T2> constexpr bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)’
454 | operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
| ^~~~~~~~
/usr/include/c++/9/bits/stl_pair.h:454:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: ‘const Sales_data’ is not derived from ‘const std::pair<_T1, _T2>’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:331:5: note: candidate: ‘template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)’
331 | operator<(const reverse_iterator<_Iterator>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:331:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: ‘const Sales_data’ is not derived from ‘const std::reverse_iterator<_Iterator>’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:369:5: note: candidate: ‘template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)’
369 | operator<(const reverse_iterator<_IteratorL>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:369:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: ‘const Sales_data’ is not derived from ‘const std::reverse_iterator<_Iterator>’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:1160:5: note: candidate: ‘template<class _IteratorL, class _IteratorR> bool std::operator<(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)’
1160 | operator<(const move_iterator<_IteratorL>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:1160:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: ‘const Sales_data’ is not derived from ‘const std::move_iterator<_IteratorL>’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:1166:5: note: candidate: ‘template<class _Iterator> bool std::operator<(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorL>&)’
1166 | operator<(const move_iterator<_Iterator>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:1166:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: ‘const Sales_data’ is not derived from ‘const std::move_iterator<_IteratorL>’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/string:55,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/basic_string.h:6229:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
6229 | operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.h:6229:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: ‘const Sales_data’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/string:55,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/basic_string.h:6242:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)’
6242 | operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.h:6242:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: ‘const Sales_data’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/string:55,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/basic_string.h:6254:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
6254 | operator<(const _CharT* __lhs,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.h:6254:5: note: template argument deduction/substitution failed:
sales_data.cc:90:6: note: mismatched types ‘const _CharT*’ and ‘Sales_data’
90 | if(a<b)
| ~^~
In file included from /usr/include/c++/9/bits/ios_base.h:46,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/system_error:208:3: note: candidate: ‘bool std::operator<(const std::error_code&, const std::error_code&)’
208 | operator<(const error_code& __lhs, const error_code& __rhs) noexcept
| ^~~~~~~~
/usr/include/c++/9/system_error:208:31: note: no known conversion for argument 1 from ‘const Sales_data’ to ‘const std::error_code&’
208 | operator<(const error_code& __lhs, const error_code& __rhs) noexcept
| ~~~~~~~~~~~~~~~~~~^~~~~
/usr/include/c++/9/system_error:282:3: note: candidate: ‘bool std::operator<(const std::error_condition&, const std::error_condition&)’
282 | operator<(const error_condition& __lhs,
| ^~~~~~~~
/usr/include/c++/9/system_error:282:36: note: no known conversion for argument 1 from ‘const Sales_data’ to ‘const std::error_condition&’
282 | operator<(const error_condition& __lhs,
| ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
sales_data.cc:92:12: error: no match for ‘operator<’ (operand types are ‘const Sales_data’ and ‘const Sales_data’)
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:64,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_pair.h:454:5: note: candidate: ‘template<class _T1, class _T2> constexpr bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)’
454 | operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
| ^~~~~~~~
/usr/include/c++/9/bits/stl_pair.h:454:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: ‘const Sales_data’ is not derived from ‘const std::pair<_T1, _T2>’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:331:5: note: candidate: ‘template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)’
331 | operator<(const reverse_iterator<_Iterator>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:331:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: ‘const Sales_data’ is not derived from ‘const std::reverse_iterator<_Iterator>’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:369:5: note: candidate: ‘template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)’
369 | operator<(const reverse_iterator<_IteratorL>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:369:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: ‘const Sales_data’ is not derived from ‘const std::reverse_iterator<_Iterator>’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:1160:5: note: candidate: ‘template<class _IteratorL, class _IteratorR> bool std::operator<(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)’
1160 | operator<(const move_iterator<_IteratorL>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:1160:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: ‘const Sales_data’ is not derived from ‘const std::move_iterator<_IteratorL>’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/bits/stl_algobase.h:67,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/stl_iterator.h:1166:5: note: candidate: ‘template<class _Iterator> bool std::operator<(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorL>&)’
1166 | operator<(const move_iterator<_Iterator>& __x,
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator.h:1166:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: ‘const Sales_data’ is not derived from ‘const std::move_iterator<_IteratorL>’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/string:55,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/basic_string.h:6229:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
6229 | operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.h:6229:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: ‘const Sales_data’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/string:55,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/basic_string.h:6242:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)’
6242 | operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.h:6242:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: ‘const Sales_data’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/string:55,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/bits/basic_string.h:6254:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
6254 | operator<(const _CharT* __lhs,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.h:6254:5: note: template argument deduction/substitution failed:
sales_data.cc:92:12: note: mismatched types ‘const _CharT*’ and ‘Sales_data’
92 | else if (b<a)
| ~^~
In file included from /usr/include/c++/9/bits/ios_base.h:46,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from sales_data.cc:30:
/usr/include/c++/9/system_error:208:3: note: candidate: ‘bool std::operator<(const std::error_code&, const std::error_code&)’
208 | operator<(const error_code& __lhs, const error_code& __rhs) noexcept
| ^~~~~~~~
/usr/include/c++/9/system_error:208:31: note: no known conversion for argument 1 from ‘const Sales_data’ to ‘const std::error_code&’
208 | operator<(const error_code& __lhs, const error_code& __rhs) noexcept
| ~~~~~~~~~~~~~~~~~~^~~~~
/usr/include/c++/9/system_error:282:3: note: candidate: ‘bool std::operator<(const std::error_condition&, const std::error_condition&)’
282 | operator<(const error_condition& __lhs,
| ^~~~~~~~
/usr/include/c++/9/system_error:282:36: note: no known conversion for argument 1 from ‘const Sales_data’ to ‘const std::error_condition&’
282 | operator<(const error_condition& __lhs,
| ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
sales_data.cc: In function ‘int compare(const T&, const T&) [with T = Sales_data]’:
sales_data.cc:96:1: warning: control reaches end of non-void function [-Wreturn-type]
96 | }
