STL的set有test_and_set功能

test_and_set是这个意思:

/*
UINT32&    u = hb[h >> 5];
const UINT32    m = 1 << (h & 0x1f);
const UINT32    seen = u & m;
u |= m;    // test_and_set
*/
#include <iostream>
#include <set>
using namespace std;
int main() {
    set<int>    s;
    pair<set<int>::iterator,bool>    p = s.insert(1);
    cout << p.second << endl;
    p = s.insert(1);
    cout << p.second << endl;
    cout << s.size() << endl;
}

http://www.cplusplus.com/reference/set/set/insert/

一句 cout << p,五颜六色的错误信息爆屏,正好250行:

STL的set有test_and_set功能
test.cpp: In function 'int main()':
test.cpp:17:7: error: no match for 'operator<<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'std::pair<std::_Rb_tree_const_iterator<int>, bool>')
   17 |  cout << p;
      |  ~~~~ ^~ ~
      |  |       |
      |  |       std::pair<std::_Rb_tree_const_iterator<int>, bool>
      |  std::ostream {aka std::basic_ostream<char>}
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:108:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  108 |       operator<<(__ostream_type& (*__pf)(__ostream_type&))
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:108:36: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'std::basic_ostream<char>::__ostream_type& (*)(std::basic_ostream<char>::__ostream_type&)' {aka 'std::basic_ostream<char>& (*)(std::basic_ostream<char>&)'}
  108 |       operator<<(__ostream_type& (*__pf)(__ostream_type&))
      |                  ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:117:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>; std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]'
  117 |       operator<<(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:117:32: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'std::basic_ostream<char>::__ios_type& (*)(std::basic_ostream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'}
  117 |       operator<<(__ios_type& (*__pf)(__ios_type&))
      |                  ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:127:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  127 |       operator<<(ios_base& (*__pf) (ios_base&))
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:127:30: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'std::ios_base& (*)(std::ios_base&)'
  127 |       operator<<(ios_base& (*__pf) (ios_base&))
      |                  ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:166:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  166 |       operator<<(long __n)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:166:23: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'long int'
  166 |       operator<<(long __n)
      |                  ~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:170:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  170 |       operator<<(unsigned long __n)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:170:32: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'long unsigned int'
  170 |       operator<<(unsigned long __n)
      |                  ~~~~~~~~~~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:174:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  174 |       operator<<(bool __n)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:174:23: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'bool'
  174 |       operator<<(bool __n)
      |                  ~~~~~^~~
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:784,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:91:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char; _Traits = std::char_traits<char>]'
   91 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:92:22: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'short int'
   92 |     operator<<(short __n)
      |                ~~~~~~^~~
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:181:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  181 |       operator<<(unsigned short __n)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:181:33: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'short unsigned int'
  181 |       operator<<(unsigned short __n)
      |                  ~~~~~~~~~~~~~~~^~~
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:784,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:105:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits<char>]'
  105 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:106:20: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'int'
  106 |     operator<<(int __n)
      |                ~~~~^~~
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:192:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  192 |       operator<<(unsigned int __n)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:192:31: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'unsigned int'
  192 |       operator<<(unsigned int __n)
      |                  ~~~~~~~~~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:201:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  201 |       operator<<(long long __n)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:201:28: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'long long int'
  201 |       operator<<(long long __n)
      |                  ~~~~~~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:205:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  205 |       operator<<(unsigned long long __n)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:205:37: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'long long unsigned int'
  205 |       operator<<(unsigned long long __n)
      |                  ~~~~~~~~~~~~~~~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:220:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  220 |       operator<<(double __f)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:220:25: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'double'
  220 |       operator<<(double __f)
      |                  ~~~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:224:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  224 |       operator<<(float __f)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:224:24: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'float'
  224 |       operator<<(float __f)
      |                  ~~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:232:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  232 |       operator<<(long double __f)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:232:30: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'long double'
  232 |       operator<<(long double __f)
      |                  ~~~~~~~~~~~~^~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:245:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]'
  245 |       operator<<(const void* __p)
      |       ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:245:30: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'const void*'
  245 |       operator<<(const void* __p)
      |                  ~~~~~~~~~~~~^~~
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:784,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:119:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]'
  119 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:120:34: note:   no known conversion for argument 1 from 'std::pair<std::_Rb_tree_const_iterator<int>, bool>' to 'std::basic_ostream<char>::__streambuf_type*' {aka 'std::basic_streambuf<char>*'}
  120 |     operator<<(__streambuf_type* __sbin)
      |                ~~~~~~~~~~~~~~~~~~^~~~~~
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/string:55,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/locale_classes.h:40,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ios_base.h:41,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ios:42,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:38,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/basic_string.h:6468:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)'
 6468 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/basic_string.h:6468:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   'std::pair<std::_Rb_tree_const_iterator<int>, bool>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ios_base.h:46,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ios:42,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:38,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/system_error:262:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::error_code&)'
  262 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/system_error:262:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'const std::error_code&'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:506:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, _CharT)'
  506 |     operator<<(basic_ostream<_CharT, _Traits>& ___out, _CharT __c)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:506:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   deduced conflicting types for parameter '_CharT' ('char' and 'std::pair<std::_Rb_tree_const_iterator<int>, bool>')
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:511:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, char)'
  511 |     operator<<(basic_ostream<_CharT, _Traits>& ___out, char __c)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:511:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'char'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:517:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, char)'
  517 |     operator<<(basic_ostream<char, _Traits>& ___out, char __c)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:517:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'char'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:523:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, signed char)'
  523 |     operator<<(basic_ostream<char, _Traits>& ___out, signed char __c)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:523:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'signed char'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:528:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, unsigned char)'
  528 |     operator<<(basic_ostream<char, _Traits>& ___out, unsigned char __c)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:528:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'unsigned char'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:589:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const _CharT*)'
  589 |     operator<<(basic_ostream<_CharT, _Traits>& ___out, const _CharT* __s)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:589:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   mismatched types 'const _CharT*' and 'std::pair<std::_Rb_tree_const_iterator<int>, bool>'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:784,
                 from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:321:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const char*)'
  321 |     operator<<(basic_ostream<_CharT, _Traits>& ___out, const char* __s)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/bits/ostream.tcc:321:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'const char*'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:606:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const char*)'
  606 |     operator<<(basic_ostream<char, _Traits>& ___out, const char* __s)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:606:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'const char*'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:619:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const signed char*)'
  619 |     operator<<(basic_ostream<char, _Traits>& ___out, const signed char* __s)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:619:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'const signed char*'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:624:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const unsigned char*)'
  624 |     operator<<(basic_ostream<char, _Traits>& ___out, const unsigned char* __s)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:624:5: note:   template argument deduction/substitution failed:
test.cpp:17:10: note:   cannot convert 'p' (type 'std::pair<std::_Rb_tree_const_iterator<int>, bool>') to type 'const unsigned char*'
   17 |  cout << p;
      |          ^
In file included from d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/iostream:39,
                 from test.cpp:7:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:773:5: note: candidate: 'template<class _Ostream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_ostream<_Ostream>, std::__is_insertable<typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type, const _Tp&, void> >::value, typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type>::type std::operator<<(_Ostream&&, const _Tp&)'
  773 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:773:5: note:   template argument deduction/substitution failed:
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream: In substitution of 'template<class _Ostream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_ostream<_Ostream>, std::__is_insertable<typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type, const _Tp&, void> >::value, typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type>::type std::operator<<(_Ostream&&, const _Tp&) [with _Ostream = std::basic_ostream<char>&; _Tp = std::pair<std::_Rb_tree_const_iterator<int>, bool>]':
test.cpp:17:10:   required from here
d:/gcc/lib/gcc/mingw32/10.3.0/include/c++/ostream:773:5: error: no type named 'type' in 'struct std::enable_if<false, std::basic_ostream<char>&>'
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