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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

6.5.6 Elaborated type specifiers [basic.lookup.elab] C++N4910:2022 (19) p54.cpp

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はじめに(Introduction)

N4910 Working Draft, Standard for Programming Language C++

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。

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

C++N4741, 2018 Standard Working Draft on ISO/IEC 14882 sample code compile list

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++

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.

6.5.6 Elaborated type specifiers [basic.lookup.elab] C++N4910:2022 (19) p54.cpp

算譜(source code)

p54.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 * msg="6.5.6 Elaborated type specifiers [basic.lookup.elab] C++N4910:2022 (19) p54.cpp";
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>
#include <cstdlib>
#include <cstring>

using namespace std;

// [Example 1 :

struct Node {
struct Node* Next; // OK, refers to injected-class-name Node
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 (9.2.9.4)
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 (9.2.9.4)
struct Base::Data; // error: cannot introduce a qualified type (9.2.9.4)
struct Base::Datum; // error: Datum undefined
struct Base::Data* pBase; // OK, refers to nested Data

int main() { 
  cout<< msg << endl;
  return EXIT_SUCCESS;
}

Script

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)

bash
# ./clgc.sh p54
rm: cannot remove 'p54l': No such file or directory
rm: cannot remove 'p54g': No such file or directory
$ clang++ p54.cpp -std=03 -o p54l -I. -Wall
p54.cpp:20:17: error: no struct named 'Glob' in the global namespace
friend struct ::Glob; // error: Glob is not declared, cannot introduce a qualified type (9.2.9.4)
              ~~^
p54.cpp:28:8: warning: class 'Data' was previously declared as a struct; this is valid, but may result in linker errors under the Microsoft C++ ABI [-Wmismatched-tags]
friend class ::Data; // OK, global Data is a friend
       ^
p54.cpp:18:8: note: previous use is here
struct Data {
       ^
p54.cpp:28:8: note: did you mean struct here?
friend class ::Data; // OK, global Data is a friend
       ^~~~~
       struct
p54.cpp:29:8: warning: class 'Data' was previously declared as a struct; this is valid, but may result in linker errors under the Microsoft C++ ABI [-Wmismatched-tags]
friend class Data; // OK, nested Data is a friend
       ^
p54.cpp:25:8: note: previous use is here
struct Data; // OK, declares nested Data
       ^
p54.cpp:33:10: warning: extra qualification on member 'Data' [-Wextra-qualification]
struct ::Data; // error: cannot introduce a qualified type (9.2.9.4)
         ^
p54.cpp:33:8: error: forward declaration of struct cannot have a nested name specifier
struct ::Data; // error: cannot introduce a qualified type (9.2.9.4)
       ^~
p54.cpp:34:8: error: forward declaration of struct cannot have a nested name specifier
struct Base::Data; // error: cannot introduce a qualified type (9.2.9.4)
       ^~~~~~
p54.cpp:35:14: error: no struct named 'Datum' in 'Base'
struct Base::Datum; // error: Datum undefined
       ~~~~~~^
3 warnings and 4 errors generated.
rm: cannot remove 'p54l': No such file or directory
$ clang++ p54.cpp -std=2b -o p54l -I. -Wall
p54.cpp:20:17: error: no struct named 'Glob' in the global namespace
friend struct ::Glob; // error: Glob is not declared, cannot introduce a qualified type (9.2.9.4)
              ~~^
p54.cpp:28:8: warning: class 'Data' was previously declared as a struct; this is valid, but may result in linker errors under the Microsoft C++ ABI [-Wmismatched-tags]
friend class ::Data; // OK, global Data is a friend
       ^
p54.cpp:18:8: note: previous use is here
struct Data {
       ^
p54.cpp:28:8: note: did you mean struct here?
friend class ::Data; // OK, global Data is a friend
       ^~~~~
       struct
p54.cpp:29:8: warning: class 'Data' was previously declared as a struct; this is valid, but may result in linker errors under the Microsoft C++ ABI [-Wmismatched-tags]
friend class Data; // OK, nested Data is a friend
       ^
p54.cpp:25:8: note: previous use is here
struct Data; // OK, declares nested Data
       ^
p54.cpp:33:10: warning: extra qualification on member 'Data' [-Wextra-qualification]
struct ::Data; // error: cannot introduce a qualified type (9.2.9.4)
         ^
p54.cpp:33:8: error: forward declaration of struct cannot have a nested name specifier
struct ::Data; // error: cannot introduce a qualified type (9.2.9.4)
       ^~
p54.cpp:34:8: error: forward declaration of struct cannot have a nested name specifier
struct Base::Data; // error: cannot introduce a qualified type (9.2.9.4)
       ^~~~~~
p54.cpp:35:14: error: no struct named 'Datum' in 'Base'
struct Base::Datum; // error: Datum undefined
       ~~~~~~^
3 warnings and 4 errors generated.

$ g++ p54.cpp -std=03 -o p54g -I. -Wall
p54.cpp:20:17: error: 'Glob' in namespace '::' does not name a type
   20 | friend struct ::Glob; // error: Glob is not declared, cannot introduce a qualified type (9.2.9.4)
      |                 ^~~~
p54.cpp:20:1: error: friend declaration does not name a class or function
   20 | friend struct ::Glob; // error: Glob is not declared, cannot introduce a qualified type (9.2.9.4)
      | ^~~~~~
p54.cpp:33:10: warning: declaration 'struct Data' does not declare anything
   33 | struct ::Data; // error: cannot introduce a qualified type (9.2.9.4)
      |          ^~~~
p54.cpp:34:14: warning: declaration 'struct Base::Data' does not declare anything
   34 | struct Base::Data; // error: cannot introduce a qualified type (9.2.9.4)
      |              ^~~~
p54.cpp:35:14: error: 'Datum' in 'struct Base' does not name a type
   35 | struct Base::Datum; // error: Datum undefined
      |              ^~~~~
rm: cannot remove 'p54g': No such file or directory

$ g++ p54.cpp -std=2b -o p54g -I. -Wall
p54.cpp:20:17: error: 'Glob' in namespace '::' does not name a type
   20 | friend struct ::Glob; // error: Glob is not declared, cannot introduce a qualified type (9.2.9.4)
      |                 ^~~~
p54.cpp:20:1: error: friend declaration does not name a class or function
   20 | friend struct ::Glob; // error: Glob is not declared, cannot introduce a qualified type (9.2.9.4)
      | ^~~~~~
p54.cpp:33:10: warning: declaration 'struct Data' does not declare anything
   33 | struct ::Data; // error: cannot introduce a qualified type (9.2.9.4)
      |          ^~~~
p54.cpp:34:14: warning: declaration 'struct Base::Data' does not declare anything
   34 | struct Base::Data; // error: cannot introduce a qualified type (9.2.9.4)
      |              ^~~~
p54.cpp:35:14: error: 'Datum' in 'struct Base' does not name a type
   35 | struct Base::Datum; // error: Datum undefined
      |              ^~~~~

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。

参考資料(reference)

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

dockerにclang

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

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

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

C++ sample list

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
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. 0.01 初稿 　20220619

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