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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

C++ N4606 (69)7.1.7.1 The cv-qualifiers [dcl.type.cv] p.164

Last updated at Posted at 2018-04-17

#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。

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.

#(69)7.1.7.1 The cv-qualifiers [dcl.type.cv]
p.164

p164.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p164.cpp(69)7.1.7.1 The cv-qualifiers [dcl.type.cv]"

#include <iostream>

const int ci = 3; // cv-qualified (initialized as required)
ci = 4; // ill-formed: attempt to modify const
int i = 2; // not cv-qualified
const int* cip; // pointer to const int
cip = &i; // OK: cv-qualified access path to unqualified
cip = 4; // ill-formed: attempt to modify through ptr to const
int ip;
ip = const_cast(cip); // cast needed to convert const int* to int*
ip = 4; // defined: *ip points to i, a non-const object
const int ciq = new const int (3); // initialized as required
int* iq = const_cast(ciq); // cast required
*iq = 4; // undefined: modifies a const object
struct X {
  mutable int i;
  int j;
};
struct Y {
  X x;
  Y();
};
const Y y;
y.x.i++; // well-formed: mutable member can be modified
y.x.j++; // ill-formed: const-qualified member modified
Y* p = const_cast(&y); // cast away const-ness of y
p->x.i = 99; // well-formed: mutable member can be modified
p->x.j = 99; // undefined: modifies a const member
int main(){
  int i=1;
  foo(i);
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p164
$ clang++ p164.cpp
p164.cpp:8:1: error: C++ requires a type specifier for all declarations
ci = 4; // ill-formed: attempt to modify const
^
p164.cpp:11:1: error: C++ requires a type specifier for all declarations
cip = &i; // OK: cv-qualified access path to unqualified
^
p164.cpp:12:1: error: C++ requires a type specifier for all declarations
cip = 4; // ill-formed: attempt to modify through ptr to const
^
p164.cpp:14:1: error: C++ requires a type specifier for all declarations
ip = const_cast(cip); // cast needed to convert const int* to int*
^
p164.cpp:14:16: error: expected '<' after 'const_cast'
ip = const_cast(cip); // cast needed to convert const int* to int*
               ^
               <
p164.cpp:15:1: error: C++ requires a type specifier for all declarations
ip = 4; // defined: *ip points to i, a non-const object
^
p164.cpp:16:11: error: cannot initialize a variable of type 'const int' with an rvalue of type 'const int *'
const int ciq = new const int (3); // initialized as required
          ^     ~~~~~~~~~~~~~~~~~
p164.cpp:17:21: error: expected '<' after 'const_cast'
int* iq = const_cast(ciq); // cast required
                    ^
                    <
p164.cpp:18:2: error: C++ requires a type specifier for all declarations
*iq = 4; // undefined: modifies a const object
 ^
p164.cpp:28:1: error: unknown type name 'y'
y.x.i++; // well-formed: mutable member can be modified
^
p164.cpp:28:2: error: cannot use dot operator on a type
y.x.i++; // well-formed: mutable member can be modified
 ^
p164.cpp:29:1: error: unknown type name 'y'
y.x.j++; // ill-formed: const-qualified member modified
^
p164.cpp:29:2: error: cannot use dot operator on a type
y.x.j++; // ill-formed: const-qualified member modified
 ^
p164.cpp:30:18: error: expected '<' after 'const_cast'
Y* p = const_cast(&y); // cast away const-ness of y
                 ^
                 <
p164.cpp:31:1: error: unknown type name 'p'
p->x.i = 99; // well-formed: mutable member can be modified
^
p164.cpp:31:2: error: cannot use arrow operator on a type
p->x.i = 99; // well-formed: mutable member can be modified
 ^
p164.cpp:32:1: error: unknown type name 'p'
p->x.j = 99; // undefined: modifies a const member
^
p164.cpp:32:2: error: cannot use arrow operator on a type
p->x.j = 99; // undefined: modifies a const member
 ^
18 errors generated.

$ g++-7 p164.cpp
p164.cpp:8:1: error: 'ci' does not name a type
 ci = 4; // ill-formed: attempt to modify const
 ^~
p164.cpp:11:1: error: 'cip' does not name a type
 cip = &i; // OK: cv-qualified access path to unqualified
 ^~~
p164.cpp:12:1: error: 'cip' does not name a type
 cip = 4; // ill-formed: attempt to modify through ptr to const
 ^~~
p164.cpp:14:1: error: 'ip' does not name a type
 ip = const_cast(cip); // cast needed to convert const int* to int*
 ^~
p164.cpp:15:1: error: 'ip' does not name a type
 ip = 4; // defined: *ip points to i, a non-const object
 ^~
p164.cpp:16:33: error: invalid conversion from 'const int*' to 'int' [-fpermissive]
 const int ciq = new const int (3); // initialized as required
                                 ^
p164.cpp:17:21: error: expected '<' before '(' token
 int* iq = const_cast(ciq); // cast required
                     ^
p164.cpp:17:21: error: expected type-specifier before '(' token
p164.cpp:17:21: error: expected '>' before '(' token
p164.cpp:18:5: error: expected constructor, destructor, or type conversion before '=' token
 *iq = 4; // undefined: modifies a const object
     ^
p164.cpp:28:1: error: 'y' does not name a type
 y.x.i++; // well-formed: mutable member can be modified
 ^
p164.cpp:29:1: error: 'y' does not name a type
 y.x.j++; // ill-formed: const-qualified member modified
 ^
p164.cpp:30:18: error: expected '<' before '(' token
 Y* p = const_cast(&y); // cast away const-ness of y
                  ^
p164.cpp:30:18: error: expected type-specifier before '(' token
p164.cpp:30:18: error: expected '>' before '(' token
p164.cpp:31:1: error: 'p' does not name a type
 p->x.i = 99; // well-formed: mutable member can be modified
 ^
p164.cpp:32:1: error: 'p' does not name a type
 p->x.j = 99; // undefined: modifies a const member
 ^

#検討事項
コンパイルエラーをなくす修正方法。
clang++とg++のコンパイルエラーの違いの背景。

#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

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

#文書履歴
0.10 初稿 2080417

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