17.11.1 Header <compare> synopsis [compare.syn] C++N4910:2022 (314) p528a.cpp

# はじめに(Introduction)

N4910  Working Draft, Standard for Programming Language C++

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/n4910.pdf

n4910は、ISO/IEC JTC1 SC22 WG21の作業原案(Working Draft)です。
公式のISO/IEC 14882原本ではありません。
ISO/IEC JTC1 SC22 WG21では、可能な限り作業文書を公開し、幅広い意見を求めています。
一連の記事はコード断片をコンパイルできる形にする方法を検討してコンパイル、リンク、実行して、規格案の原文と処理系(g++, Clang++)との違いを確認し、技術内容を検討し、ISO/IEC JTC1 SC22 WG21にフィードバックするために用います。
また、CERT C++, MISRA C++等のコーディング標準のコード断片をコンパイルする際の参考にさせていただこうと考えています。CERT C++, MISRA C++が標準化の動きとの時間的なずれがあれば確認できれば幸いです。また、boostライブラリとの関連、Linux OS, TOPPERSカーネル、g++(GCC), clang++(LLVM）との関係も調査中です。
何か、抜け漏れ、耳より情報がありましたらおしらせくださると幸いです。

 <この項は書きかけです。順次追記します。>

## 背景(back ground)
C/C++でコンパイルエラーが出ると、途方にくれることがしばしばあります。
何回かに１回は、該当するエラーが検索できます。
ただ、条件が違っていて、そこでの修正方法では目的を達成しないこともしばしばです。いろいろな条件のコンパイルエラーとその対応方法について、広く記録することによって、いつか同じエラーに遭遇した時にやくに立つことを目指しています。

この半年の間で、三度、自分のネットでの記録に助けられたことがあります。
また過去に解決できなかった記録を１０種類以上、最近になって解決できたことがあります。それは、主に次の３つの情報に基づいています。

https://stackoverflow.com
https://cpprefjp.github.io
http://ja.cppreference.com/

また
https://researchmap.jp/joub9b3my-1797580/#_1797580
に記載したサイトのお世話になっています。

## 作業方針(sequence)
Clang++では-std=c++03, C++2bの2種類
g++では-std=c++03, c++2bの２種類
でコンパイルし、

１）コンパイルエラーを収集する。
２）コンパイルエラーをなくす方法を検討する。
コンパイルエラーになる例を示すだけが目的のコードは、コンパイルエラーをなくすのではなく、コンパイルエラーの種類を収集するだけにする。
文法を示すのが目的のコード場合に、コンパイルエラーをなくすのに手間がかかる場合は、順次作業します。
３）リンクエラーをなくす方法を検討する。
文法を示すのが目的のコード場合に、リンクエラーをなくすのに手間がかかる場合は、順次作業します。
４）意味のある出力を作る。
コンパイル、リンクが通っても、意味のある出力を示そうとすると、コンパイル・リンクエラーが出て収拾できそうにない場合がある。順次作業します。

１）だけのものから４）まで進んだものと色々ある状態です。一歩でも前に進むご助言をお待ちしています。「検討事項」の欄に現状を記録するようにしています。

### C++N4910:2022 Standard Working Draft on ISO/IEC 14882(0) sample code compile list  

https://qiita.com/kaizen_nagoya/items/fc957ddddd402004bb91

### C++N4741, 2018 Standard Working Draft on ISO/IEC 14882 sample code compile list
https://qiita.com/kaizen_nagoya/items/3294c014044550896010

### C++N4606, 2016符号断片編纂一覧(example code compile list)
C++N4606, 2016 Working Draft 2016, ISO/IEC 14882, C++ standard(1) Example code compile list
https://qiita.com/kaizen_nagoya/items/df5d62c35bd6ed1c3d43/

### C++N3242, 2011 sample code compile list on clang++ and g++
https://qiita.com/kaizen_nagoya/items/685b5c1a2c17c1bf1318

## 編纂器(Compiler)
### clang++ --version
> Debian clang version 14.0.5-++20220610033153+c12386ae247c-1~exp1~20220610153237.151
Target: x86_64-pc-linux-gnu, Thread model: posix, InstalledDir: /usr/bin

### g++- --version
> g++ (GCC) 12.1.0  Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# 17.11.1 Header <compare> synopsis [compare.syn] C++N4910:2022 (314) p528a.cpp

## 算譜(source code)

```c++:p528a.cpp
// C++N4910 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/n4910.pdf
const char * n4910 = "17.11.1 Header <compare> synopsis [compare.syn] C++N4910:2022 (314) p528a.cpp";
// Debian clang version 14.0.5-++20220610033153+c12386ae247c-
// g++ (GCC) 12.1.0 Copyright (C) 2022 Free Software Foundation, Inc.
// Edited by Dr. OGAWA Kiyoshi. Compile procedure and results record.
// C++N4910:2022 Standard Working Draft on ISO/IEC 14882(0) sample code compile list
// https://qiita.com/kaizen_nagoya/items/fc957ddddd402004bb91

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <coroutine>
#include <vector>
#include <complex>
#include <map>
#include <atomic>
#include <unordered_map>
#include <typeinfo>

using namespace std;

// Example 1
namespace std {
// 17.11.2, comparison category types class partial_ordering;
class weak_ordering;
class strong_ordering;
// named comparison functions
constexpr bool is_eq  (partial_ordering cmp) noexcept {
    return cmp == 0;
}
constexpr bool is_neq (partial_ordering cmp) noexcept {
    return cmp != 0;
}
constexpr bool is_lt  (partial_ordering cmp) noexcept {
    return cmp < 0;
}
constexpr bool is_lteq(partial_ordering cmp) noexcept {
    return cmp <= 0;
}
constexpr bool is_gt  (partial_ordering cmp) noexcept {
    return cmp > 0;
}
constexpr bool is_gteq(partial_ordering cmp) noexcept {
    return cmp >= 0;
}
// 17.11.3, common comparison category type
template<class... Ts>
struct common_comparison_category {
    using type = see_below;
};
template<class... Ts>
using common_comparison_category_t = typename common_comparison_category<Ts...>::type;
// 17.11.4, concept three_way_comparable
template<class T, class Cat = partial_ordering>
concept three_way_comparable = see_below;
template<class T, class U, class Cat = partial_ordering>
concept three_way_comparable_with = see_below;
// 17.11.5, result of three-way comparison
template<class T, class U = T> struct compare_three_way_result;
template<class T, class U = T>
using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;
//  The header <compare> specifies types, objects, and functions for use primarily in connection with the
inline namespace unspecified {
inline constexpr unspecified strong_order= unspecified ;
inline constexpr unspecified weak_order = unspecified ;
inline constexpr unspecified partial_order = unspecified ;
inline constexpr unspecified compare_strong_order_fallback unspecified = unspecified ;
inline constexpr compare_weak_order_fallback = unspecified;
inline constexpr compare_partial_order_fallback = unspecified ;
}
}
int main() {
    cout  <<  n4910 << endl;
    return EXIT_SUCCESS;
}
```

## Script

```bash:clgc.sh
#!/bin/sh
rm $1l
rm $1g
echo "$ clang++ $1.cpp -std=03 -o $1l -I. -Wall" 
clang++ $1.cpp -std=c++03 -o $1l -I. -Wall
if [  -e $1l ]; then
./$1l 
fi
rm $1l
echo "$ clang++ $1.cpp -std=2b -o $1l -I. -Wall"
clang++ $1.cpp -std=c++2b -o $1l -I. -Wall
if [  -e $1l ]; then
./$1l
fi
echo "\r"
echo "$ g++ $1.cpp -std=03 -o $1g -I. -Wall"
g++ $1.cpp -std=c++03 -o $1g -I. -Wall
if [ -e $1g ]; then
./$1g
fi
rm $1g
echo "\r"
echo "$ g++ $1.cpp -std=2b -o $1g -I. -Wall"
g++ $1.cpp -std=c++2b -o $1g -I. -Wall
if [ -e $1g ]; then
./$1g 
fi
```
## 編纂・実行結果(compile and go)

```ubuntu:bash
# ./clgc.sh p528a
$ clang++ p528a.cpp -std=c++03 -o p528al -I. -Wall
In file included from p528a.cpp:19:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/atomic:38:
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/c++0x_warning.h:32:2: error: This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
#error This file requires compiler and library support \
 ^
p528a.cpp:31:5: error: unknown type name 'constexpr'
    constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
    ^
p528a.cpp:31:28: error: unknown type name 'partial_ordering'
    constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
                           ^
p528a.cpp:31:50: error: expected function body after function declarator
    constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
                                                 ^
p528a.cpp:42:19: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
    template<class... Ts>
                  ^
p528a.cpp:43:44: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
      using common_comparison_category_t = typename common_comparison_category<Ts...>::type;
                                           ^
p528a.cpp:43:53: error: no template named 'common_comparison_category'
      using common_comparison_category_t = typename common_comparison_category<Ts...>::type;
                                                    ^
p528a.cpp:45:31: error: unknown type name 'partial_ordering'
template<class T, class Cat = partial_ordering>
                              ^
p528a.cpp:46:1: error: unknown type name 'concept'
concept three_way_comparable = see_below; 
^
p528a.cpp:46:9: warning: variable templates are a C++14 extension [-Wc++14-extensions]
concept three_way_comparable = see_below; 
        ^
p528a.cpp:46:32: error: use of undeclared identifier 'see_below'
concept three_way_comparable = see_below; 
                               ^
p528a.cpp:47:40: error: unknown type name 'partial_ordering'
template<class T, class U, class Cat = partial_ordering>
                                       ^
p528a.cpp:48:1: error: unknown type name 'concept'
concept three_way_comparable_with = see_below; 
^
p528a.cpp:48:9: warning: variable templates are a C++14 extension [-Wc++14-extensions]
concept three_way_comparable_with = see_below; 
        ^
p528a.cpp:48:37: error: use of undeclared identifier 'see_below'
concept three_way_comparable_with = see_below; 
                                    ^
p528a.cpp:52:42: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
      using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;
                                         ^
p528a.cpp:54:1: warning: inline namespaces are a C++11 feature [-Wc++11-inline-namespace]
inline namespace unspecified {
^
p528a.cpp:55:8: error: unknown type name 'constexpr'
inline constexpr unspecified strong_order= unspecified ; 
       ^
p528a.cpp:55:1: warning: inline variables are a C++17 extension [-Wc++17-extensions]
inline constexpr unspecified strong_order= unspecified ; 
^
p528a.cpp:55:29: error: expected ';' after top level declarator
inline constexpr unspecified strong_order= unspecified ; 
                            ^
                            ;
p528a.cpp:56:8: error: unknown type name 'constexpr'
inline constexpr unspecified weak_order = unspecified ;
       ^
p528a.cpp:56:1: warning: inline variables are a C++17 extension [-Wc++17-extensions]
inline constexpr unspecified weak_order = unspecified ;
^
p528a.cpp:56:29: error: expected ';' after top level declarator
inline constexpr unspecified weak_order = unspecified ;
                            ^
                            ;
p528a.cpp:57:8: error: unknown type name 'constexpr'
inline constexpr unspecified partial_order = unspecified ; 
       ^
p528a.cpp:57:1: warning: inline variables are a C++17 extension [-Wc++17-extensions]
inline constexpr unspecified partial_order = unspecified ; 
^
p528a.cpp:57:29: error: expected ';' after top level declarator
inline constexpr unspecified partial_order = unspecified ; 
                            ^
                            ;
p528a.cpp:58:8: error: unknown type name 'constexpr'
inline constexpr unspecified compare_strong_order_fallback unspecified = unspecified ;
       ^
p528a.cpp:58:1: warning: inline variables are a C++17 extension [-Wc++17-extensions]
inline constexpr unspecified compare_strong_order_fallback unspecified = unspecified ;
^
p528a.cpp:58:29: error: expected ';' after top level declarator
inline constexpr unspecified compare_strong_order_fallback unspecified = unspecified ;
                            ^
                            ;
fatal error: too many errors emitted, stopping now [-ferror-limit=]
10 warnings and 20 errors generated.
rm: cannot remove 'p528al': No such file or directory
$ clang++ p528a.cpp -std=c++2b -o p528al -I. -Wall
p528a.cpp:31:20: error: redefinition of 'is_eq'
    constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
                   ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:320:3: note: previous definition is here
  is_eq(partial_ordering __cmp) noexcept
  ^
p528a.cpp:32:20: error: redefinition of 'is_neq'
    constexpr bool is_neq (partial_ordering cmp) noexcept { return cmp != 0; }
                   ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:324:3: note: previous definition is here
  is_neq(partial_ordering __cmp) noexcept
  ^
p528a.cpp:33:20: error: redefinition of 'is_lt'
    constexpr bool is_lt  (partial_ordering cmp) noexcept { return cmp < 0; }
                   ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:328:3: note: previous definition is here
  is_lt  (partial_ordering __cmp) noexcept
  ^
p528a.cpp:34:20: error: redefinition of 'is_lteq'
    constexpr bool is_lteq(partial_ordering cmp) noexcept { return cmp <= 0; }
                   ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:332:3: note: previous definition is here
  is_lteq(partial_ordering __cmp) noexcept
  ^
p528a.cpp:35:20: error: redefinition of 'is_gt'
    constexpr bool is_gt  (partial_ordering cmp) noexcept { return cmp > 0; }
                   ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:336:3: note: previous definition is here
  is_gt  (partial_ordering __cmp) noexcept
  ^
p528a.cpp:36:20: error: redefinition of 'is_gteq'
    constexpr bool is_gteq(partial_ordering cmp) noexcept { return cmp >= 0; }
                   ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:340:3: note: previous definition is here
  is_gteq(partial_ordering __cmp) noexcept
  ^
p528a.cpp:39:8: error: redefinition of 'common_comparison_category'
struct common_comparison_category {
       ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:377:12: note: previous definition is here
    struct common_comparison_category
           ^
p528a.cpp:46:32: error: use of undeclared identifier 'see_below'
concept three_way_comparable = see_below; 
                               ^
p528a.cpp:48:37: error: use of undeclared identifier 'see_below'
concept three_way_comparable_with = see_below; 
                                    ^
p528a.cpp:50:33: error: template parameter redefines default argument
    template<class T, class U = T> struct compare_three_way_result;
                                ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:469:41: note: previous default template argument defined here
  template<typename _Tp, typename _Up = _Tp>
                                        ^
p528a.cpp:52:13: error: type alias template redefinition with different types ('typename compare_three_way_result<T, U>::type' vs 'typename __detail::__cmp3way_res_impl<_Tp, _Up>::type')
      using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;
            ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:476:11: note: previous definition is here
    using compare_three_way_result_t
          ^
p528a.cpp:51:33: error: template parameter redefines default argument
    template<class T, class U = T>
                                ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/compare:475:41: note: previous default template argument defined here
  template<typename _Tp, typename _Up = _Tp>
                                        ^
p528a.cpp:55:18: error: unknown type name 'unspecified'
inline constexpr unspecified strong_order= unspecified ; 
                 ^
p528a.cpp:55:44: error: unexpected namespace name 'unspecified': expected expression
inline constexpr unspecified strong_order= unspecified ; 
                                           ^
p528a.cpp:56:18: error: unknown type name 'unspecified'
inline constexpr unspecified weak_order = unspecified ;
                 ^
p528a.cpp:56:43: error: unexpected namespace name 'unspecified': expected expression
inline constexpr unspecified weak_order = unspecified ;
                                          ^
p528a.cpp:57:18: error: unknown type name 'unspecified'
inline constexpr unspecified partial_order = unspecified ; 
                 ^
p528a.cpp:57:46: error: unexpected namespace name 'unspecified': expected expression
inline constexpr unspecified partial_order = unspecified ; 
                                             ^
p528a.cpp:58:18: error: unknown type name 'unspecified'
inline constexpr unspecified compare_strong_order_fallback unspecified = unspecified ;
                 ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.

$ g++ p528a.cpp -std=c++03 -o p528ag -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from p528a.cpp:19:
/usr/local/include/c++/12.1.0/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
   32 | #error This file requires compiler and library support \
      |  ^~~~~
p528a.cpp:31:5: warning: identifier 'constexpr' is a keyword in C++11 [-Wc++11-compat]
   31 |     constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
      |     ^~~~~~~~~
p528a.cpp:31:50: warning: identifier 'noexcept' is a keyword in C++11 [-Wc++11-compat]
   31 |     constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
      |                                                  ^~~~~~~~
p528a.cpp:31:5: error: 'constexpr' does not name a type
   31 |     constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
      |     ^~~~~~~~~
p528a.cpp:31:5: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:32:5: error: 'constexpr' does not name a type
   32 |     constexpr bool is_neq (partial_ordering cmp) noexcept { return cmp != 0; }
      |     ^~~~~~~~~
p528a.cpp:32:5: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:33:5: error: 'constexpr' does not name a type
   33 |     constexpr bool is_lt  (partial_ordering cmp) noexcept { return cmp < 0; }
      |     ^~~~~~~~~
p528a.cpp:33:5: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:34:5: error: 'constexpr' does not name a type
   34 |     constexpr bool is_lteq(partial_ordering cmp) noexcept { return cmp <= 0; }
      |     ^~~~~~~~~
p528a.cpp:34:5: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:35:5: error: 'constexpr' does not name a type
   35 |     constexpr bool is_gt  (partial_ordering cmp) noexcept { return cmp > 0; }
      |     ^~~~~~~~~
p528a.cpp:35:5: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:36:5: error: 'constexpr' does not name a type
   36 |     constexpr bool is_gteq(partial_ordering cmp) noexcept { return cmp >= 0; }
      |     ^~~~~~~~~
p528a.cpp:36:5: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:38:15: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   38 | template<class... Ts>
      |               ^~~
p528a.cpp:40:7: error: expected nested-name-specifier before 'type'
   40 | using type = see_below;
      |       ^~~~
p528a.cpp:42:19: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   42 |     template<class... Ts>
      |                   ^~~
p528a.cpp:43:7: error: expected unqualified-id before 'using'
   43 |       using common_comparison_category_t = typename common_comparison_category<Ts...>::type;
      |       ^~~~~
p528a.cpp:45:31: error: 'partial_ordering' does not name a type; did you mean 'weak_ordering'?
   45 | template<class T, class Cat = partial_ordering>
      |                               ^~~~~~~~~~~~~~~~
      |                               weak_ordering
p528a.cpp:46:1: error: 'concept' does not name a type
   46 | concept three_way_comparable = see_below;
      | ^~~~~~~
p528a.cpp:46:1: note: 'concept' only available with '-std=c++20' or '-fconcepts'
p528a.cpp:47:40: error: 'partial_ordering' does not name a type; did you mean 'weak_ordering'?
   47 | template<class T, class U, class Cat = partial_ordering>
      |                                        ^~~~~~~~~~~~~~~~
      |                                        weak_ordering
p528a.cpp:48:1: error: 'concept' does not name a type
   48 | concept three_way_comparable_with = see_below;
      | ^~~~~~~
p528a.cpp:48:1: note: 'concept' only available with '-std=c++20' or '-fconcepts'
p528a.cpp:52:7: error: expected unqualified-id before 'using'
   52 |       using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;
      |       ^~~~~
p528a.cpp:55:8: error: 'constexpr' does not name a type
   55 | inline constexpr unspecified strong_order= unspecified ;
      |        ^~~~~~~~~
p528a.cpp:55:8: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:56:8: error: 'constexpr' does not name a type
   56 | inline constexpr unspecified weak_order = unspecified ;
      |        ^~~~~~~~~
p528a.cpp:56:8: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:57:8: error: 'constexpr' does not name a type
   57 | inline constexpr unspecified partial_order = unspecified ;
      |        ^~~~~~~~~
p528a.cpp:57:8: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:58:8: error: 'constexpr' does not name a type
   58 | inline constexpr unspecified compare_strong_order_fallback unspecified = unspecified ;
      |        ^~~~~~~~~
p528a.cpp:58:8: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:59:8: error: 'constexpr' does not name a type
   59 | inline constexpr compare_weak_order_fallback = unspecified;
      |        ^~~~~~~~~
p528a.cpp:59:8: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p528a.cpp:60:8: error: 'constexpr' does not name a type
   60 | inline constexpr compare_partial_order_fallback = unspecified ;
      |        ^~~~~~~~~
p528a.cpp:60:8: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
rm: cannot remove 'p528ag': No such file or directory

$ g++ p528a.cpp -std=c++2b -o p528ag -I. -Wall
p528a.cpp:31:20: error: redefinition of 'constexpr bool std::is_eq(partial_ordering)'
   31 |     constexpr bool is_eq  (partial_ordering cmp) noexcept { return cmp == 0; }
      |                    ^~~~~
In file included from /usr/local/include/c++/12.1.0/bits/char_traits.h:45,
                 from /usr/local/include/c++/12.1.0/ios:40,
                 from /usr/local/include/c++/12.1.0/ostream:38,
                 from /usr/local/include/c++/12.1.0/iostream:39,
                 from p528a.cpp:10:
/usr/local/include/c++/12.1.0/compare:360:3: note: 'constexpr bool std::is_eq(partial_ordering)' previously defined here
  360 |   is_eq(partial_ordering __cmp) noexcept
      |   ^~~~~
p528a.cpp:32:20: error: redefinition of 'constexpr bool std::is_neq(partial_ordering)'
   32 |     constexpr bool is_neq (partial_ordering cmp) noexcept { return cmp != 0; }
      |                    ^~~~~~
/usr/local/include/c++/12.1.0/compare:365:3: note: 'constexpr bool std::is_neq(partial_ordering)' previously defined here
  365 |   is_neq(partial_ordering __cmp) noexcept
      |   ^~~~~~
p528a.cpp:33:20: error: redefinition of 'constexpr bool std::is_lt(partial_ordering)'
   33 |     constexpr bool is_lt  (partial_ordering cmp) noexcept { return cmp < 0; }
      |                    ^~~~~
/usr/local/include/c++/12.1.0/compare:370:3: note: 'constexpr bool std::is_lt(partial_ordering)' previously defined here
  370 |   is_lt  (partial_ordering __cmp) noexcept
      |   ^~~~~
p528a.cpp:34:20: error: redefinition of 'constexpr bool std::is_lteq(partial_ordering)'
   34 |     constexpr bool is_lteq(partial_ordering cmp) noexcept { return cmp <= 0; }
      |                    ^~~~~~~
/usr/local/include/c++/12.1.0/compare:375:3: note: 'constexpr bool std::is_lteq(partial_ordering)' previously defined here
  375 |   is_lteq(partial_ordering __cmp) noexcept
      |   ^~~~~~~
p528a.cpp:35:20: error: redefinition of 'constexpr bool std::is_gt(partial_ordering)'
   35 |     constexpr bool is_gt  (partial_ordering cmp) noexcept { return cmp > 0; }
      |                    ^~~~~
/usr/local/include/c++/12.1.0/compare:380:3: note: 'constexpr bool std::is_gt(partial_ordering)' previously defined here
  380 |   is_gt  (partial_ordering __cmp) noexcept
      |   ^~~~~
p528a.cpp:36:20: error: redefinition of 'constexpr bool std::is_gteq(partial_ordering)'
   36 |     constexpr bool is_gteq(partial_ordering cmp) noexcept { return cmp >= 0; }
      |                    ^~~~~~~
/usr/local/include/c++/12.1.0/compare:385:3: note: 'constexpr bool std::is_gteq(partial_ordering)' previously defined here
  385 |   is_gteq(partial_ordering __cmp) noexcept
      |   ^~~~~~~
p528a.cpp:39:8: error: redefinition of 'struct std::common_comparison_category<_Ts>'
   39 | struct common_comparison_category {
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/c++/12.1.0/compare:422:12: note: previous definition of 'struct std::common_comparison_category<_Ts>'
  422 |     struct common_comparison_category
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~
p528a.cpp:46:32: error: 'see_below' was not declared in this scope
   46 | concept three_way_comparable = see_below;
      |                                ^~~~~~~~~
p528a.cpp:46:9: error: redefinition of 'template<class T, class Cat> concept std::three_way_comparable'
   46 | concept three_way_comparable = see_below;
      |         ^~~~~~~~~~~~~~~~~~~~
/usr/local/include/c++/12.1.0/compare:463:13: note: 'template<class _Tp, class _Cat> concept std::three_way_comparable' previously declared here
  463 |     concept three_way_comparable
      |             ^~~~~~~~~~~~~~~~~~~~
p528a.cpp:48:37: error: 'see_below' was not declared in this scope
   48 | concept three_way_comparable_with = see_below;
      |                                     ^~~~~~~~~
p528a.cpp:48:9: error: redefinition of 'template<class T, class U, class Cat> concept std::three_way_comparable_with'
   48 | concept three_way_comparable_with = see_below;
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/c++/12.1.0/compare:473:13: note: 'template<class _Tp, class _Up, class _Cat> concept std::three_way_comparable_with' previously declared here
  473 |     concept three_way_comparable_with
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~
p528a.cpp:50:23: error: redefinition of default argument for 'class U'
   50 |     template<class T, class U = T> struct compare_three_way_result;
      |                       ^~~~~
/usr/local/include/c++/12.1.0/compare:514:26: note: original definition appeared here
  514 |   template<typename _Tp, typename _Up = _Tp>
      |                          ^~~~~~~~
p528a.cpp:52:13: error: conflicting declaration of template 'template<class T, class U> using compare_three_way_result_t = typename std::compare_three_way_result::type'
   52 |       using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/c++/12.1.0/compare:521:11: note: previous declaration 'template<class _Tp, class _Up> using compare_three_way_result_t = typename std::__detail::__cmp3way_res_impl::type'
  521 |     using compare_three_way_result_t
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~
p528a.cpp:55:18: error: 'unspecified' does not name a type
   55 | inline constexpr unspecified strong_order= unspecified ;
      |                  ^~~~~~~~~~~
p528a.cpp:56:18: error: 'unspecified' does not name a type
   56 | inline constexpr unspecified weak_order = unspecified ;
      |                  ^~~~~~~~~~~
p528a.cpp:57:18: error: 'unspecified' does not name a type
   57 | inline constexpr unspecified partial_order = unspecified ;
      |                  ^~~~~~~~~~~
p528a.cpp:58:18: error: 'unspecified' does not name a type
   58 | inline constexpr unspecified compare_strong_order_fallback unspecified = unspecified ;
      |                  ^~~~~~~~~~~
p528a.cpp:59:18: error: 'compare_weak_order_fallback' does not name a type
   59 | inline constexpr compare_weak_order_fallback = unspecified;
      |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
p528a.cpp:60:18: error: 'compare_partial_order_fallback' does not name a type
   60 | inline constexpr compare_partial_order_fallback = unspecified ;
      |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

```

## 検討事項(agenda)
コンパイルエラーを取るか、コンパイルエラーの理由を解説する。

<!-- リンクエラーの解説をする。clang++とg++の比較。意味のある出力。
コンパイルエラーを取るか、コンパイルエラーの理由を解説する。-->


# 参考資料(reference)

cpprefjp - C++日本語リファレンス

https://cpprefjp.github.io/

コンパイラの実装状況

https://cpprefjp.github.io/implementation-status.html


typedef は C++11 ではオワコン

https://qiita.com/Linda_pp/items/44a67c64c14cba00eef1

C99からC++14を駆け抜けるC++講座

https://qiita.com/yumetodo/items/e49a673afd9a3ecb81a8

## 自己参照(self reference)

コピペコンパイルエラーあるある

https://qiita.com/kaizen_nagoya/items/29c832de9d762aed2761

C++ Error Message Collection(1)does not name a type, 11 articles

https://qiita.com/kaizen_nagoya/items/acb9f1a9b5aad6df06bd

dockerにclang

https://qiita.com/kaizen_nagoya/items/8829ffeee397eda50e80

docker gnu(gcc/g++) and llvm(clang/clang++)

https://qiita.com/drafts/059874ea39c4de64c0f7

コンパイル用shell script C版(clangとgcc)とC++版(clang++とg++)

https://qiita.com/kaizen_nagoya/items/74220c0577a512c2d7da

Compare the contents of C++N4910:2022, C++N4741:2018 and C++N4606:2015

https://qiita.com/kaizen_nagoya/items/483246d40f98abff7ded

C++ sample list

https://qiita.com/kaizen_nagoya/items/54ad75b73825b7c04f86


clang++, g++コンパイルエラー方針の違いの例

https://qiita.com/kaizen_nagoya/items/ea6e5009fe126d270a82

astyle 使ってみた

https://qiita.com/kaizen_nagoya/items/3c9a87a781d53a1a23f3

C++N4606 Working Draft 2016, ISO/IEC 14882, C++ standardのコード断片をコンパイルするためにしていること
https://qiita.com/kaizen_nagoya/items/a8d7ee2f2e29e76c19c1

コンパイル用shell script C版(clangとgcc)とC++版(clang++とg++)
https://qiita.com/kaizen_nagoya/items/74220c0577a512c2d7da

Clang/Clang++(LLVM) gcc/g++(GNU) コンパイラ警告等比較
https://qiita.com/kaizen_nagoya/items/9a82b958cc3aeef0403f

C++2003とC++2017でコンパイルエラーになるならない事例集
https://qiita.com/kaizen_nagoya/items/a13ea3823441c430edff

Qiitaに投稿するCのStyle例(暫定)
https://qiita.com/kaizen_nagoya/items/946df1528a6a1ef2bc0d

cpprefjpのdecltypeをコンパイル試験
https://qiita.com/kaizen_nagoya/items/090909af702f0d5d8a67

MISRA C++ 5-0-16
https://qiita.com/kaizen_nagoya/items/7df2d4e05db724752a74

C++ Templates Part1 BASICS Chapter 3. Class Templates 3.2 Use of Class Template Stack stack1test.cpp
https://qiita.com/kaizen_nagoya/items/cd5fc49106fad5a4e9ed

ISO/IEC TS 17961:2013 C Secure Coding Rules(1) All list(to be confirmed)
https://qiita.com/kaizen_nagoya/items/54e056195c4f11b850a1

C言語（C++)に対する誤解、曲解、無理解、爽快。
https://qiita.com/kaizen_nagoya/items/3f3992c9722c1cee2e3a

C Puzzle Bookの有り難み5つ、C言語規格及びCコンパイラの特性を認識
https://qiita.com/kaizen_nagoya/items/d89a48c1536a02ecdec9

'wchar.h' file not found で困った clang++ macOS
https://qiita.com/kaizen_nagoya/items/de15cd46d657517fac11

Open POSIX Test Suiteの使い方を調べはじめました
https://qiita.com/kaizen_nagoya/items/644d5e407f5faf96e6dc

MISRA-C 2012 Referenceに掲載している文献の入手可能性を確認
https://qiita.com/kaizen_nagoya/items/96dc8b125e462d5575bb

どうやって MISRA Example Suiteをコンパイルするか
https://qiita.com/kaizen_nagoya/items/fbdbff5ff696e2ca7f00

MISRA C まとめ #include <misra_c.h>
https://qiita.com/kaizen_nagoya/items/f1a79a7cbd281607c7c9

「C++完全理解ガイド」の同意できること上位10
https://qiita.com/kaizen_nagoya/items/aa5744e0c4a8618c7671


 ＜この記事は個人の過去の経験に基づく個人の感想です。現在所属する組織、業務とは関係がありません。＞

# 文書履歴(document history)
ver. 0.01 初稿 　20220710