N4606 Working Draft 2016, ISO/IEC 14882, C++ standard(20)3.4.4 Elaborated type specifiers [basic.lookup.elab] p.59

# はじめに
N4606 Working Draft, Standard for Programming Language C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/#mailing2016-11
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf

n4606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擦れの確認が結果としてできれば幸いです。

## list
N4606 Working Draft 2016, ISO/IEC 14882, C++ standard(1) coding list
https://qiita.com/kaizen_nagoya/items/df5d62c35bd6ed1c3d43/


## Compiler
### clang++ --version
clang version 6.0.0 (tags/RELEASE_600/final)

### g++-7 --version
g++-7 (Homebrew GCC 7.3.0_1) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.


#(20)3.4.4 Elaborated type specifiers [basic.lookup.elab]
p.59

```c++:p59.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p59.cpp (20)3.4.4 Elaborated type specifiers [basic.lookup.elab]"

#include <iostream>

struct Node {
  struct Node* Next; // OK: Refers to Node at global scope
  struct Data* Data; // OK: Declares type Data
// at global scope and member Data
};
struct Data {
  struct Node* Node; // OK: Refers to Node at global scope
  friend struct ::Glob; // error: Glob is not declared
  // cannot introduce a qualified type (7.1.7.3)
  friend struct Glob; // OK: Refers to (as yet) undeclared Glob
  // at global scope.
  /* ... */
};
struct Base {
  struct Data; // OK: Declares nested Data
  struct ::Data* thatData; // OK: Refers to ::Data
  struct Base::Data* thisData; // OK: Refers to nested Data
  friend class ::Data; // OK: global Data is a friend
  friend class Data; // OK: nested Data is a friend
  struct Data { /* ... */ }; // Defines nested Data
};
struct Data; // OK: Redeclares Data at global scope
struct ::Data; // error: cannot introduce a qualified type (7.1.7.3)
struct Base::Data; // error: cannot introduce a qualified type (7.1.7.3)
struct Base::Datum; // error: Datum undefined
struct Base::Data* pBase; // OK: refers to nested Data

int main(int argc, char *argv[], char *envp[]){
  std::cout << msg << std::endl;
  return EXIT_SUCCESS;
}
```

```shell_session
$ ./cppgl.sh p59
$ clang++ p59.cpp
p59.cpp:15:17: error: no struct named 'Glob' in the global namespace
friend struct ::Glob; // error: Glob is not declared
              ~~^
p59.cpp:30:10: warning: extra qualification on member 'Data' [-Wextra-qualification]
struct ::Data; // error: cannot introduce a qualified type (7.1.7.3)
         ^
p59.cpp:30:8: error: forward declaration of struct cannot have a nested name specifier
struct ::Data; // error: cannot introduce a qualified type (7.1.7.3)
       ^~
p59.cpp:31:8: error: forward declaration of struct cannot have a nested name specifier
struct Base::Data; // error: cannot introduce a qualified type (7.1.7.3)
       ^~~~~~
p59.cpp:32:14: error: no struct named 'Datum' in 'Base'
struct Base::Datum; // error: Datum undefined
       ~~~~~~^
1 warning and 4 errors generated.

$ g++-7 p59.cpp
p59.cpp:15:17: error: 'Glob' in namespace '::' does not name a type
 friend struct ::Glob; // error: Glob is not declared
                 ^~~~
p59.cpp:15:1: error: friend declaration does not name a class or function
 friend struct ::Glob; // error: Glob is not declared
 ^~~~~~
p59.cpp:30:10: warning: declaration 'struct Data' does not declare anything
 struct ::Data; // error: cannot introduce a qualified type (7.1.7.3)
          ^~~~
p59.cpp:31:14: warning: declaration 'struct Base::Data' does not declare anything
 struct Base::Data; // error: cannot introduce a qualified type (7.1.7.3)
              ^~~~
p59.cpp:32:14: error: 'Datum' in 'struct Base' does not name a type
 struct Base::Datum; // error: Datum undefined
              ^~~~~
```

# 検討事項
　コンパイルエラーにならない変更。
　内容の出力。

# 参考資料

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
Qiitaに投稿するCのStyle例(暫定)
https://qiita.com/kaizen_nagoya/items/946df1528a6a1ef2bc0d
# 文書履歴
ver. 0.10 初稿 2080415
ver. 0.11 URL追記　20230215
### 最後までおよみいただきありがとうございました。
いいね　💚、フォローをお願いします。
####  Thank you very much for reading to the last sentence.
Please press the like icon 💚　and follow me for your happy life.