6.5.3 Unqualified name lookup [basic.lookup.unqual] C++N4910:2022 (14) p45.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。

## 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.

# 6.5.3 Unqualified name lookup [basic.lookup.unqual] C++N4910:2022 (14) p45.cpp



## 算譜(source code)

```c++:p45.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="6.5.3 Unqualified name lookup [basic.lookup.unqual] C++N4910:2022 (14) p45.cpp";
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

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

using namespace std;

// [Example 1 :
struct T1 { struct U { int i; }; };
struct T2 { };
struct U1 {};
struct U2 {};
struct B {
using T = T1;
using U = U1;
operator U1 T1::*();
operator U1 T2::*();
operator U2 T1::*();
operator U2 T2::*();
};
template<class X, class T>
int g() {
using U = U2;
X().operator U T::*(); // #1, searches for T in the scope of X first
X().operator U decltype(T())::*(); // #2
return 0;
}
int x = g<B, T2>(); // #1 calls B::operator U1 T1::*
// #2 calls B::operator U1 T2::*
// Example 2 :
using I = int;
using D = double;
namespace A {
inline namespace N {using C = char; }
using F = float;
void f(I);
void f(D);
void f(C);
void f(F);
}
struct X0 {using F = float; };
struct W {
using D = void;
struct X : X0 {
void g(I);
void g(::D);
void g(F);
};
};
namespace B2 {
typedef short I, F;
class Y {
friend void A::f(I); // error: no void A::f(short)
friend void A::f(D); // OK
friend void A::f(C); // error: A::N::C not found
friend void A::f(F); // OK
friend void W::X::g(I); // error: no void X::g(short)
friend void W::X::g(D); // OK
friend void W::X::g(F); // OK
};
}

int main() { 
  cout<< msg << 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)


```shell_session:clgc.sh
# ./clgc.sh p45
rm: cannot remove 'p45l': No such file or directory
rm: cannot remove 'p45g': No such file or directory
$ clang++ p45.cpp -std=03 -o p45l -I. -Wall
p45.cpp:18:11: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using T = T1;
          ^
p45.cpp:19:11: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using U = U1;
          ^
p45.cpp:27:11: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using U = U2;
          ^
p45.cpp:29:15: error: expected ';' after expression
X().operator U decltype(T())::*(); // #2
              ^
              ;
p45.cpp:29:29: error: expected ';' after expression
X().operator U decltype(T())::*(); // #2
                            ^
                            ;
p45.cpp:29:31: error: expected unqualified-id
X().operator U decltype(T())::*(); // #2
                              ^
p45.cpp:29:33: error: expected expression
X().operator U decltype(T())::*(); // #2
                                ^
p45.cpp:35:11: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using I = int;
          ^
p45.cpp:36:11: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using D = double;
          ^
p45.cpp:38:1: warning: inline namespaces are a C++11 feature [-Wc++11-inline-namespace]
inline namespace N {using C = char; }
^
p45.cpp:38:31: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
inline namespace N {using C = char; }
                              ^
p45.cpp:39:11: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using F = float;
          ^
p45.cpp:45:22: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
struct X0 {using F = float; };
                     ^
p45.cpp:47:11: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using D = void;
          ^
p45.cpp:57:16: error: friend declaration of 'f' does not match any declaration in namespace 'A'
friend void A::f(I); // error: no void A::f(short)
               ^
p45.cpp:40:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'I' (aka 'int'))
void f(I);
     ^
p45.cpp:41:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'D' (aka 'double'))
void f(D);
     ^
p45.cpp:42:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'A::C' (aka 'char'))
void f(C);
     ^
p45.cpp:43:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'A::F' (aka 'float'))
void f(F);
     ^
p45.cpp:59:18: error: unknown type name 'C'; did you mean 'A::C'?
friend void A::f(C); // error: A::N::C not found
                 ^
                 A::C
p45.cpp:38:27: note: 'A::C' declared here
inline namespace N {using C = char; }
                          ^
p45.cpp:60:16: error: friend declaration of 'f' does not match any declaration in namespace 'A'
friend void A::f(F); // OK
               ^
p45.cpp:40:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'I' (aka 'int'))
void f(I);
     ^
p45.cpp:41:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'D' (aka 'double'))
void f(D);
     ^
p45.cpp:42:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'A::C' (aka 'char'))
void f(C);
     ^
p45.cpp:43:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'A::F' (aka 'float'))
void f(F);
     ^
p45.cpp:62:19: error: friend declaration of 'g' does not match any declaration in 'W::X'
friend void W::X::g(D); // OK
                  ^
p45.cpp:49:6: note: candidate function has different number of parameters (expected 0 but has 1)
void g(I);
     ^
p45.cpp:50:6: note: candidate function has different number of parameters (expected 0 but has 1)
void g(::D);
     ^
p45.cpp:51:6: note: candidate function has different number of parameters (expected 0 but has 1)
void g(F);
     ^
p45.cpp:29:5: error: no member named 'operator U2' in 'B'
X().operator U decltype(T())::*(); // #2
~~~ ^
p45.cpp:32:9: note: in instantiation of function template specialization 'g<B, T2>' requested here
int x = g<B, T2>(); // #1 calls B::operator U1 T1::*
        ^
p45.cpp:29:16: error: use of undeclared identifier 'decltype'
X().operator U decltype(T())::*(); // #2
               ^
10 warnings and 10 errors generated.
rm: cannot remove 'p45l': No such file or directory
$ clang++ p45.cpp -std=2b -o p45l -I. -Wall
p45.cpp:57:16: error: friend declaration of 'f' does not match any declaration in namespace 'A'
friend void A::f(I); // error: no void A::f(short)
               ^
p45.cpp:40:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'I' (aka 'int'))
void f(I);
     ^
p45.cpp:41:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'D' (aka 'double'))
void f(D);
     ^
p45.cpp:42:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'A::C' (aka 'char'))
void f(C);
     ^
p45.cpp:43:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::I' (aka 'short') but has 'A::F' (aka 'float'))
void f(F);
     ^
p45.cpp:59:18: error: unknown type name 'C'; did you mean 'A::C'?
friend void A::f(C); // error: A::N::C not found
                 ^
                 A::C
p45.cpp:38:27: note: 'A::C' declared here
inline namespace N {using C = char; }
                          ^
p45.cpp:60:16: error: friend declaration of 'f' does not match any declaration in namespace 'A'
friend void A::f(F); // OK
               ^
p45.cpp:40:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'I' (aka 'int'))
void f(I);
     ^
p45.cpp:41:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'D' (aka 'double'))
void f(D);
     ^
p45.cpp:42:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'A::C' (aka 'char'))
void f(C);
     ^
p45.cpp:43:6: note: candidate function has type mismatch at 1st parameter (expected 'B2::F' (aka 'short') but has 'A::F' (aka 'float'))
void f(F);
     ^
p45.cpp:62:19: error: friend declaration of 'g' does not match any declaration in 'W::X'
friend void W::X::g(D); // OK
                  ^
p45.cpp:49:6: note: candidate function has different number of parameters (expected 0 but has 1)
void g(I);
     ^
p45.cpp:50:6: note: candidate function has different number of parameters (expected 0 but has 1)
void g(::D);
     ^
p45.cpp:51:6: note: candidate function has different number of parameters (expected 0 but has 1)
void g(F);
     ^
4 errors generated.

$ g++ p45.cpp -std=03 -o p45g -I. -Wall
p45.cpp:29:16: warning: identifier 'decltype' is a keyword in C++11 [-Wc++11-compat]
   29 | X().operator U decltype(T())::*(); // #2
      |                ^~~~~~~~
p45.cpp:18:7: error: expected nested-name-specifier before 'T'
   18 | using T = T1;
      |       ^
p45.cpp:19:7: error: expected nested-name-specifier before 'U'
   19 | using U = U1;
      |       ^
p45.cpp: In function 'int g()':
p45.cpp:27:7: error: expected nested-name-specifier before 'U'
   27 | using U = U2;
      |       ^
p45.cpp:28:14: error: 'U' does not name a type
   28 | X().operator U T::*(); // #1, searches for T in the scope of X first
      |              ^
p45.cpp:29:14: error: 'U' does not name a type
   29 | X().operator U decltype(T())::*(); // #2
      |              ^
p45.cpp: At global scope:
p45.cpp:35:7: error: expected nested-name-specifier before 'I'
   35 | using I = int;
      |       ^
p45.cpp:36:7: error: expected nested-name-specifier before 'D'
   36 | using D = double;
      |       ^
p45.cpp:38:27: error: expected nested-name-specifier before 'C'
   38 | inline namespace N {using C = char; }
      |                           ^
p45.cpp:39:7: error: expected nested-name-specifier before 'F'
   39 | using F = float;
      |       ^
p45.cpp:40:6: error: variable or field 'f' declared void
   40 | void f(I);
      |      ^
p45.cpp:40:8: error: 'I' was not declared in this scope
   40 | void f(I);
      |        ^
p45.cpp:41:6: error: variable or field 'f' declared void
   41 | void f(D);
      |      ^
p45.cpp:41:8: error: 'D' was not declared in this scope
   41 | void f(D);
      |        ^
p45.cpp:42:6: error: variable or field 'f' declared void
   42 | void f(C);
      |      ^
p45.cpp:42:8: error: 'C' was not declared in this scope
   42 | void f(C);
      |        ^
p45.cpp:43:6: error: variable or field 'f' declared void
   43 | void f(F);
      |      ^
p45.cpp:43:8: error: 'F' was not declared in this scope
   43 | void f(F);
      |        ^
p45.cpp:45:18: error: expected nested-name-specifier before 'F'
   45 | struct X0 {using F = float; };
      |                  ^
p45.cpp:47:7: error: expected nested-name-specifier before 'D'
   47 | using D = void;
      |       ^
p45.cpp:49:8: error: 'I' has not been declared
   49 | void g(I);
      |        ^
p45.cpp:50:10: error: '::D' has not been declared
   50 | void g(::D);
      |          ^
p45.cpp:50:6: error: 'void W::X::g(int)' cannot be overloaded with 'void W::X::g(int)'
   50 | void g(::D);
      |      ^
p45.cpp:49:6: note: previous declaration 'void W::X::g(int)'
   49 | void g(I);
      |      ^
p45.cpp:51:8: error: 'F' has not been declared
   51 | void g(F);
      |        ^
p45.cpp:51:6: error: 'void W::X::g(int)' cannot be overloaded with 'void W::X::g(int)'
   51 | void g(F);
      |      ^
p45.cpp:49:6: note: previous declaration 'void W::X::g(int)'
   49 | void g(I);
      |      ^
p45.cpp:57:18: error: 'I' has not been declared
   57 | friend void A::f(I); // error: no void A::f(short)
      |                  ^
p45.cpp:57:19: error: 'void A::f(int)' should have been declared inside 'A'
   57 | friend void A::f(I); // error: no void A::f(short)
      |                   ^
p45.cpp:58:18: error: 'D' has not been declared
   58 | friend void A::f(D); // OK
      |                  ^
p45.cpp:58:13: warning: 'void A::f(int)' has not been declared within 'A'
   58 | friend void A::f(D); // OK
      |             ^
p45.cpp:57:13: note: only here as a 'friend'
   57 | friend void A::f(I); // error: no void A::f(short)
      |             ^
p45.cpp:59:18: error: 'C' has not been declared
   59 | friend void A::f(C); // error: A::N::C not found
      |                  ^
p45.cpp:59:13: warning: 'void A::f(int)' has not been declared within 'A'
   59 | friend void A::f(C); // error: A::N::C not found
      |             ^
p45.cpp:58:13: note: only here as a 'friend'
   58 | friend void A::f(D); // OK
      |             ^
p45.cpp:60:18: error: 'F' has not been declared
   60 | friend void A::f(F); // OK
      |                  ^
p45.cpp:60:13: warning: 'void A::f(int)' has not been declared within 'A'
   60 | friend void A::f(F); // OK
      |             ^
p45.cpp:59:13: note: only here as a 'friend'
   59 | friend void A::f(C); // error: A::N::C not found
      |             ^
p45.cpp:61:21: error: 'I' has not been declared
   61 | friend void W::X::g(I); // error: no void X::g(short)
      |                     ^
p45.cpp:62:21: error: 'D' has not been declared
   62 | friend void W::X::g(D); // OK
      |                     ^
p45.cpp:63:21: error: 'F' has not been declared
   63 | friend void W::X::g(F); // OK
      |                     ^
rm: cannot remove 'p45g': No such file or directory

$ g++ p45.cpp -std=2b -o p45g -I. -Wall
p45.cpp:62:13: error: no declaration matches 'void W::X::g()'
   62 | friend void W::X::g(D); // OK
      |             ^
p45.cpp:51:6: note: candidates are: 'void W::X::g(X0::F)'
   51 | void g(F);
      |      ^
p45.cpp:50:6: note:                 'void W::X::g(D)'
   50 | void g(::D);
      |      ^
p45.cpp:49:6: note:                 'void W::X::g(I)'
   49 | void g(I);
      |      ^
p45.cpp:48:8: note: 'struct W::X' defined here
   48 | struct X : X0 {
      |     

```

## 検討事項(agenda)


# 参考資料(reference)

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


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

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https://qiita.com/kaizen_nagoya/items/96dc8b125e462d5575bb

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https://qiita.com/kaizen_nagoya/items/fbdbff5ff696e2ca7f00

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https://qiita.com/kaizen_nagoya/items/f1a79a7cbd281607c7c9

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