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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

C++ N4606(130)11.4 Protected member access [class.protected]p277

Last updated at Posted at 2018-04-19

#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。

##作業方針
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。

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)
Target: x86_64-apple-darwin17.4.0

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

#(130)11.4 Protected member access [class.protected]p277

p277.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p277.cpp(130)11.4 Protected member access [class.protected]"
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>


class B {
protected:
int i;
static int j;
};
class D1 : public B {
};
class D2 : public B {
friend void fr(B*,D1*,D2*);
void mem(B*,D1*);
};
void fr(B* pb, D1* p1, D2* p2) {
pb->i = 1; // ill-formed
p1->i = 2; // ill-formed
p2->i = 3; // OK (access through a D2)

p2->B::i = 4; // OK (access through a D2, even though
// naming class is B)
int B::* pmi_B = &B::i; // ill-formed
int B::* pmi_B2 = &D2::i; // OK (type of &D2::i is int B::*)
B::j = 5; // ill-formed (not a friend of naming class B)
D2::j = 6; // OK (because refers to static member)
}
void D2::mem(B* pb, D1* p1) {
pb->i = 1; // ill-formed
p1->i = 2; // ill-formed
i = 3; // OK (access through this)
B::i = 4; // OK (access through this, qualification ignored)
int B::* pmi_B = &B::i; // ill-formed
int B::* pmi_B2 = &D2::i; // OK
j = 5; // OK (because j refers to static member)
B::j = 6; // OK (because B::j refers to static member)
}
void g(B* pb, D1* p1, D2* p2) {
pb->i = 1; // ill-formed
p1->i = 2; // ill-formed
p2->i = 3; // ill-formed
}

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

$ ./cppgl17.sh p277
$ clang++ p277.cpp
p277.cpp:20:5: error: 'i' is a protected member of 'B'
pb->i = 1; // ill-formed
    ^
p277.cpp:10:5: note: declared protected here
int i;
    ^
p277.cpp:21:5: error: 'i' is a protected member of 'B'
p1->i = 2; // ill-formed
    ^
p277.cpp:10:5: note: declared protected here
int i;
    ^
p277.cpp:26:22: error: 'i' is a protected member of 'B'
int B::* pmi_B = &B::i; // ill-formed
                     ^
p277.cpp:10:5: note: declared protected here
int i;
    ^
p277.cpp:28:4: error: 'j' is a protected member of 'B'
B::j = 5; // ill-formed (not a friend of naming class B)
   ^
p277.cpp:11:12: note: declared protected here
static int j;
           ^
p277.cpp:32:5: error: 'i' is a protected member of 'B'
pb->i = 1; // ill-formed
    ^
p277.cpp:10:5: note: can only access this member on an object of type 'D2'
int i;
    ^
p277.cpp:33:5: error: 'i' is a protected member of 'B'
p1->i = 2; // ill-formed
    ^
p277.cpp:10:5: note: declared protected here
int i;
    ^
p277.cpp:36:22: error: 'i' is a protected member of 'B'
int B::* pmi_B = &B::i; // ill-formed
                     ^
p277.cpp:10:5: note: must name member using the type of the current context 'D2'
int i;
    ^
p277.cpp:42:5: error: 'i' is a protected member of 'B'
pb->i = 1; // ill-formed
    ^
p277.cpp:10:5: note: declared protected here
int i;
    ^
p277.cpp:43:5: error: 'i' is a protected member of 'B'
p1->i = 2; // ill-formed
    ^
p277.cpp:10:5: note: declared protected here
int i;
    ^
p277.cpp:44:5: error: 'i' is a protected member of 'B'
p2->i = 3; // ill-formed
    ^
p277.cpp:10:5: note: declared protected here
int i;
    ^
10 errors generated.

$ g++-7 p277.cpp
p277.cpp: In function 'void fr(B*, D1*, D2*)':
p277.cpp:20:5: error: 'int B::i' is protected within this context
 pb->i = 1; // ill-formed
     ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp:21:5: error: 'int B::i' is protected within this context
 p1->i = 2; // ill-formed
     ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp:26:22: error: 'int B::i' is protected within this context
 int B::* pmi_B = &B::i; // ill-formed
                      ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp:26:22: error: 'int B::i' is protected within this context
 int B::* pmi_B = &B::i; // ill-formed
                      ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp: In member function 'void D2::mem(B*, D1*)':
p277.cpp:32:5: error: 'int B::i' is protected within this context
 pb->i = 1; // ill-formed
     ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp:33:5: error: 'int B::i' is protected within this context
 p1->i = 2; // ill-formed
     ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp:36:22: error: 'int B::i' is protected within this context
 int B::* pmi_B = &B::i; // ill-formed
                      ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp: In function 'void g(B*, D1*, D2*)':
p277.cpp:42:5: error: 'int B::i' is protected within this context
 pb->i = 1; // ill-formed
     ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp:43:5: error: 'int B::i' is protected within this context
 p1->i = 2; // ill-formed
     ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^
p277.cpp:44:5: error: 'int B::i' is protected within this context
 p2->i = 3; // ill-formed
     ^
p277.cpp:10:5: note: declared protected here
 int i;
     ^

#検討事項
コンパイルエラーをなくす修正
意味のある出力

#参考資料

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

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

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
0.10 初稿 2080420

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