C++N4741(151)15.3.2 Conversion functions [class.conv.fct]p256

#はじめに(Introduction)
C++N4741 Working Draft, Standard for Programming Language C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4741.pdf

C++N4741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。
Linux OSなどのhosted環境, TOPPERSカーネルなどのfreestanding環境におけるC++の機能と役割を確認したり、system CによるCPUの記述のtemplateによる再利用を検討しています。
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、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。

##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4つの情報に基づいています。

https://stackoverflow.com
https://cpprefjp.github.io
http://ja.cppreference.com/
https://teratail.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++17, C++2aの３種類
g++では-std=c++03, c++17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。

### コーディング標準対応
コーディング標準の検討の下準備のコードとして、
コーディング標準を守って初期化をしてある方がいいという
考え方があります。
ここでは、逆に、コンパイラの警告がどれくらいコーディング標準の検査に役立つかを確かめたいという目的があります。

何か特別なコンパイラを使っていても、将来の可搬性を考えて、
g++, clang++, visual C++の三種類のコンパイラでコンパイルできるか、
三種類のコンパイラの警告は役立たないかを確認したい。

###初期化をしない理由
しばしば変数は初期化していません。
初期化したとしても、なるべく0,1ではなく、それ以外の数を代入するようにしています。コンパイラが、どういう警告を出すか、あるいは場合によってはコンパイルエラーにするかなどを確かめるためです。
こういうコードを実際に書いて欲しいという例ではありません。

###実行する理由
実行する意味があまりなさそうなコードを実行しているのは、実行時のエラーを収集する目的です。コンパイル・リンクは通っても、実行時のエラーに何が発生する可能性があるかを収集します。
万が一、実行時にリンクする仕組みや、空間を確保するとしたら、実行しないと振る舞いがわからないことがあります。

初めての　CEDD(Compile Error Driven Design) ８回直してコンパイル。
https://qiita.com/kaizen_nagoya/items/9494236aa1753f3fd1e1

コンパイルエラーを記録するとよい理由7つ
https://qiita.com/kaizen_nagoya/items/85c0e92b206883140e89

##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
clang version 6.0.0 (tags/RELEASE_600/final)
Target: x86_64-apple-darwin17.4.0

###g++-8 --version
g++-8 (Homebrew GCC 8.1.0) 8.1.0
Copyright (C) 2018 Free Software Foundation, Inc.

#(151)15.3.2 Conversion functions [class.conv.fct]p256

C++N4606, 2016(139)12.3.2 Conversion functions [class.conv.fct]p287
https://qiita.com/kaizen_nagoya/items/b1d750c3f9955aa17962

C++N3242, 2011(120) 12.3.2 Conversion functions
https://researchmap.jp/jo8ibg2k8-1797580/#_1797580

##p256.cpp
###算譜(source code)

```c++:p256.cpp
// C++N4741 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n741.pdf
const char* msg= "C++N4741 (151)15.3.2 Conversion functions [class.conv.fct]p256.cpp";
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>
#include <cstdlib>

using namespace std;

namespace N {
  struct X {
    operator int();
    operator auto() -> short; // error: trailing return type
  };
  void f(X a) {
    int i = int(a);
    i = (int)a;
    i = a;
  }

  class Y { };
  struct Z {
    explicit operator Y() const;
  };
  void h(Z z) {
    Y y1(z); // OK: direct-initialization
    Y y2 = z; // ill-formed: copy-initialization
    Y y3 = (Y)z; // OK: cast notation
  }
  void g(X a, X b) {
    int i = (a) ? 1+a : 0;
    int j = (a&&b) ? a+b : i;
    if (a) {
    }
  }
}

namespace P {
  &ac.operator int*i; // syntax error:
// parsed as: &(ac.operator int *)i
// not as: &(ac.operator int)*i

  struct S {
    operator auto() const {
      return 10;  // OK
    }
    template<class T>
    operator auto() const {
      return 1.2;  // error: conversion function template
    }
  };
}

int main() {

  cout << msg << endl;
  return EXIT_SUCCESS;
}
```
###編纂・実行結果(compile and go)

```shell-session:c1.sh
$ ../c1.sh p256
$ clang++ p256.cpp  -std=c++2a -Wall
p256.cpp:14:20: error: cannot specify any part of a return type in the declaration of a
      conversion function; put the complete type after 'operator'
operator auto() -> short; // error: trailing return type
                   ^~~~~
p256.cpp:28:3: error: no viable conversion from 'N::Z' to 'N::Y'
Y y2 = z; // ill-formed: copy-initialization
  ^    ~
p256.cpp:22:7: note: candidate constructor (the implicit copy constructor) not viable:
      no known conversion from 'N::Z' to 'const N::Y &' for 1st argument
class Y { };
      ^
p256.cpp:22:7: note: candidate constructor (the implicit move constructor) not viable:
      no known conversion from 'N::Z' to 'N::Y &&' for 1st argument
class Y { };
      ^
p256.cpp:32:16: error: use of overloaded operator '+' is ambiguous (with operand types
      'int' and 'N::X')
int i = (a) ? 1+a : 0;
              ~^~
p256.cpp:32:16: note: because of ambiguity in conversion of 'N::X' to 'float'
p256.cpp:13:1: note: candidate function
operator int();
^
p256.cpp:14:1: note: candidate function
operator auto() -> short; // error: trailing return type
^
p256.cpp:32:16: note: built-in candidate operator+(int, float)
int i = (a) ? 1+a : 0;
               ^
p256.cpp:32:16: note: built-in candidate operator+(int, double)
p256.cpp:32:16: note: built-in candidate operator+(int, long double)
p256.cpp:32:16: note: built-in candidate operator+(int, int)
p256.cpp:32:16: note: built-in candidate operator+(int, long)
p256.cpp:32:16: note: built-in candidate operator+(int, long long)
p256.cpp:32:16: note: built-in candidate operator+(int, __int128)
p256.cpp:32:16: note: built-in candidate operator+(int, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(int, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(int, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(int, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(float, float)
p256.cpp:32:16: note: built-in candidate operator+(float, double)
p256.cpp:32:16: note: built-in candidate operator+(float, long double)
p256.cpp:32:16: note: built-in candidate operator+(float, int)
p256.cpp:32:16: note: built-in candidate operator+(float, long)
p256.cpp:32:16: note: built-in candidate operator+(float, long long)
p256.cpp:32:16: note: built-in candidate operator+(float, __int128)
p256.cpp:32:16: note: built-in candidate operator+(float, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(float, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(float, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(float, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(double, float)
p256.cpp:32:16: note: built-in candidate operator+(double, double)
p256.cpp:32:16: note: built-in candidate operator+(double, long double)
p256.cpp:32:16: note: built-in candidate operator+(double, int)
p256.cpp:32:16: note: built-in candidate operator+(double, long)
p256.cpp:32:16: note: built-in candidate operator+(double, long long)
p256.cpp:32:16: note: built-in candidate operator+(double, __int128)
p256.cpp:32:16: note: built-in candidate operator+(double, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(double, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(double, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(double, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(long double, float)
p256.cpp:32:16: note: built-in candidate operator+(long double, double)
p256.cpp:32:16: note: built-in candidate operator+(long double, long double)
p256.cpp:32:16: note: built-in candidate operator+(long double, int)
p256.cpp:32:16: note: built-in candidate operator+(long double, long)
p256.cpp:32:16: note: built-in candidate operator+(long double, long long)
p256.cpp:32:16: note: built-in candidate operator+(long double, __int128)
p256.cpp:32:16: note: built-in candidate operator+(long double, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(long double, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(long double, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(long double, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(long, float)
p256.cpp:32:16: note: built-in candidate operator+(long, double)
p256.cpp:32:16: note: built-in candidate operator+(long, long double)
p256.cpp:32:16: note: built-in candidate operator+(long, int)
p256.cpp:32:16: note: built-in candidate operator+(long, long)
p256.cpp:32:16: note: built-in candidate operator+(long, long long)
p256.cpp:32:16: note: built-in candidate operator+(long, __int128)
p256.cpp:32:16: note: built-in candidate operator+(long, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(long, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(long, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(long, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(long long, float)
p256.cpp:32:16: note: built-in candidate operator+(long long, double)
p256.cpp:32:16: note: built-in candidate operator+(long long, long double)
p256.cpp:32:16: note: built-in candidate operator+(long long, int)
p256.cpp:32:16: note: built-in candidate operator+(long long, long)
p256.cpp:32:16: note: built-in candidate operator+(long long, long long)
p256.cpp:32:16: note: built-in candidate operator+(long long, __int128)
p256.cpp:32:16: note: built-in candidate operator+(long long, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(long long, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(long long, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(long long, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(__int128, float)
p256.cpp:32:16: note: built-in candidate operator+(__int128, double)
p256.cpp:32:16: note: built-in candidate operator+(__int128, long double)
p256.cpp:32:16: note: built-in candidate operator+(__int128, int)
p256.cpp:32:16: note: built-in candidate operator+(__int128, long)
p256.cpp:32:16: note: built-in candidate operator+(__int128, long long)
p256.cpp:32:16: note: built-in candidate operator+(__int128, __int128)
p256.cpp:32:16: note: built-in candidate operator+(__int128, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(__int128, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(__int128, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(__int128, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, float)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, long double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, long long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned int, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, float)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, long double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, long long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, unsigned long long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long, unsigned __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, float)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, long double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, long long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, unsigned long
      long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned long long, unsigned
      __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, float)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, long double)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, long long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, __int128)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, unsigned int)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, unsigned long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, unsigned long
      long)
p256.cpp:32:16: note: built-in candidate operator+(unsigned __int128, unsigned
      __int128)
p256.cpp:33:10: error: conversion from 'N::X' to 'bool' is ambiguous
int j = (a&&b) ? a+b : i;
         ^
p256.cpp:13:1: note: candidate function
operator int();
^
p256.cpp:14:1: note: candidate function
operator auto() -> short; // error: trailing return type
^
p256.cpp:33:19: error: use of overloaded operator '+' is ambiguous (with operand types
      'N::X' and 'N::X')
int j = (a&&b) ? a+b : i;
                 ~^~
p256.cpp:33:19: note: because of ambiguity in conversion of 'N::X' to 'float'
p256.cpp:13:1: note: candidate function
operator int();
^
p256.cpp:14:1: note: candidate function
operator auto() -> short; // error: trailing return type
^
p256.cpp:33:19: note: because of ambiguity in conversion of 'N::X' to 'float'
int j = (a&&b) ? a+b : i;
                  ^
p256.cpp:13:1: note: candidate function
operator int();
^
p256.cpp:14:1: note: candidate function
operator auto() -> short; // error: trailing return type
^
p256.cpp:33:19: note: built-in candidate operator+(float, float)
int j = (a&&b) ? a+b : i;
                  ^
p256.cpp:33:19: note: built-in candidate operator+(float, double)
p256.cpp:33:19: note: built-in candidate operator+(float, long double)
p256.cpp:33:19: note: built-in candidate operator+(float, int)
p256.cpp:33:19: note: built-in candidate operator+(float, long)
p256.cpp:33:19: note: built-in candidate operator+(float, long long)
p256.cpp:33:19: note: built-in candidate operator+(float, __int128)
p256.cpp:33:19: note: built-in candidate operator+(float, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(float, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(float, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(float, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(double, float)
p256.cpp:33:19: note: built-in candidate operator+(double, double)
p256.cpp:33:19: note: built-in candidate operator+(double, long double)
p256.cpp:33:19: note: built-in candidate operator+(double, int)
p256.cpp:33:19: note: built-in candidate operator+(double, long)
p256.cpp:33:19: note: built-in candidate operator+(double, long long)
p256.cpp:33:19: note: built-in candidate operator+(double, __int128)
p256.cpp:33:19: note: built-in candidate operator+(double, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(double, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(double, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(double, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(long double, float)
p256.cpp:33:19: note: built-in candidate operator+(long double, double)
p256.cpp:33:19: note: built-in candidate operator+(long double, long double)
p256.cpp:33:19: note: built-in candidate operator+(long double, int)
p256.cpp:33:19: note: built-in candidate operator+(long double, long)
p256.cpp:33:19: note: built-in candidate operator+(long double, long long)
p256.cpp:33:19: note: built-in candidate operator+(long double, __int128)
p256.cpp:33:19: note: built-in candidate operator+(long double, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(long double, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(long double, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(long double, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(int, float)
p256.cpp:33:19: note: built-in candidate operator+(int, double)
p256.cpp:33:19: note: built-in candidate operator+(int, long double)
p256.cpp:33:19: note: built-in candidate operator+(int, int)
p256.cpp:33:19: note: built-in candidate operator+(int, long)
p256.cpp:33:19: note: built-in candidate operator+(int, long long)
p256.cpp:33:19: note: built-in candidate operator+(int, __int128)
p256.cpp:33:19: note: built-in candidate operator+(int, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(int, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(int, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(int, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(long, float)
p256.cpp:33:19: note: built-in candidate operator+(long, double)
p256.cpp:33:19: note: built-in candidate operator+(long, long double)
p256.cpp:33:19: note: built-in candidate operator+(long, int)
p256.cpp:33:19: note: built-in candidate operator+(long, long)
p256.cpp:33:19: note: built-in candidate operator+(long, long long)
p256.cpp:33:19: note: built-in candidate operator+(long, __int128)
p256.cpp:33:19: note: built-in candidate operator+(long, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(long, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(long, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(long, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(long long, float)
p256.cpp:33:19: note: built-in candidate operator+(long long, double)
p256.cpp:33:19: note: built-in candidate operator+(long long, long double)
p256.cpp:33:19: note: built-in candidate operator+(long long, int)
p256.cpp:33:19: note: built-in candidate operator+(long long, long)
p256.cpp:33:19: note: built-in candidate operator+(long long, long long)
p256.cpp:33:19: note: built-in candidate operator+(long long, __int128)
p256.cpp:33:19: note: built-in candidate operator+(long long, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(long long, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(long long, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(long long, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(__int128, float)
p256.cpp:33:19: note: built-in candidate operator+(__int128, double)
p256.cpp:33:19: note: built-in candidate operator+(__int128, long double)
p256.cpp:33:19: note: built-in candidate operator+(__int128, int)
p256.cpp:33:19: note: built-in candidate operator+(__int128, long)
p256.cpp:33:19: note: built-in candidate operator+(__int128, long long)
p256.cpp:33:19: note: built-in candidate operator+(__int128, __int128)
p256.cpp:33:19: note: built-in candidate operator+(__int128, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(__int128, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(__int128, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(__int128, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, float)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, long double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, long long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned int, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, float)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, long double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, long long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, unsigned long long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long, unsigned __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, float)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, long double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, long long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, unsigned long
      long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned long long, unsigned
      __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, float)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, long double)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, long long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, __int128)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, unsigned int)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, unsigned long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, unsigned long
      long)
p256.cpp:33:19: note: built-in candidate operator+(unsigned __int128, unsigned
      __int128)
p256.cpp:34:5: error: conversion from 'N::X' to 'bool' is ambiguous
if (a) {
    ^
p256.cpp:13:1: note: candidate function
operator int();
^
p256.cpp:14:1: note: candidate function
operator auto() -> short; // error: trailing return type
^
p256.cpp:40:2: error: C++ requires a type specifier for all declarations
&ac.operator int*i; // syntax error:
 ^
p256.cpp:40:2: error: declaration of reference variable 'ac' requires an initializer
&ac.operator int*i; // syntax error:
 ^~
p256.cpp:40:4: error: expected ';' after top level declarator
&ac.operator int*i; // syntax error:
   ^
   ;
9 errors generated.
```

#検討事項(agenda) 
コンパイルエラーが出ないような修正方法。
役に立つまたは意味のあるその他の出力

#参考資料(reference)

docker gnu(gcc/g++) and llvm(clang/clang++)
https://qiita.com/drafts/059874ea39c4de64c0f7

[C][C++]の国際規格案の例題をコンパイルするときの課題７つ。
https://qiita.com/kaizen_nagoya/items/5f4b155030259497c4de

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

#文書履歴(document history)
ver. 0.10 初稿 20180528