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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

C++ N4606(145)12.7 Construction and destruction [class.cdtor]p301

Last updated at Posted at 2018-04-20

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.

#(145)12.7 Construction and destruction [class.cdtor]p301

p301.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p301.cpp(145)12.7 Construction and destruction [class.cdtor]"
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>

struct X { int i; };
struct Y : X { Y(); }; // non-trivial
struct A { int a; };
struct B : public A { int j; Y y; }; // non-trivial
extern B bobj;
B* pb = &bobj; // OK
int* p1 = &bobj.a; // undefined, refers to base class member
int* p2 = &bobj.y.i; // undefined, refers to member’s member
A* pa = &bobj; // undefined, upcast to a base class type
B bobj; // definition of bobj
extern X xobj;
int* p3 = &xobj.i; //OK, X is a trivial class
X xobj;

struct W { int j; };
struct X1 : public virtual W { };
struct Y1 {
int* p;
X1 x;
Y1() : p(&x.j) { // undefined, x is not yet constructed
}
};

struct A2 { };
struct B2 : virtual A2 { };
struct C2 : B2 { };
struct D2 : virtual A2 { D2(A2*); };
struct X2 { X2(A2*); };
struct E2 : C2, D2, X2 {
E2() : D2(this), // undefined: upcast from E* to A*
// might use path E2* ! D2* ! A2*
// but D2 is not constructed
// D2((C2*)this), // defined:
// E2* ! C2* defined because E2() has started
// and C2* ! A2* defined because
// C2 fully constructed
X2(this) { // defined: upon construction of X,
// C2/B2/D2/A2 sublattice is fully constructed
}
};

struct V {
virtual void f();
virtual void g();
};
struct A3 : virtual V {
virtual void f();
};
struct B3 : virtual V {
virtual void g();
B3(V*, A3*);
};
struct D3 : A3, B3 {
virtual void f();
virtual void g();
D3() : B3((A3*)this, this) { }
};
B3::B3(V* v, A3* a) {
f(); // calls V::f, not A3::f
g(); // calls B3::g, not D3::g
v->g(); // v is base of B, the call is well-defined, calls B3::g
a->f(); // undefined behavior, a’s type not a base of B3
}

struct V4 {
virtual void f();
};
struct A4 : virtual V4 { };
struct B4 : virtual V4 {
B4(V4*, A4*);
};
struct D4 : A4, B4 {
D4() : B4((A4*)this, this) { }
};
B4::B4(V4* v, A4* a) {
typeid(*this); // type_info for B4
typeid(*v); // well-defined: *v has type V4, a base of B4
// yields type_info for B4
typeid(*a); // undefined behavior: type A4 not a base of B4
dynamic_cast<B4*>(v); // well-defined: v of type V4*, V4 base of B4
// results in B4*
dynamic_cast<B4*>(a); // undefined behavior,
// a has type A4*, A4 not a base of B4
}
int main(){
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p301
$ clang++ p301.cpp
p301.cpp:83:1: warning: expression result unused [-Wunused-value]
typeid(*this); // type_info for B4
^~~~~~~~~~~~~
p301.cpp:84:1: warning: expression result unused [-Wunused-value]
typeid(*v); // well-defined: *v has type V4, a base of B4
^~~~~~~~~~
p301.cpp:86:1: warning: expression result unused [-Wunused-value]
typeid(*a); // undefined behavior: type A4 not a base of B4
^~~~~~~~~~
p301.cpp:87:1: warning: expression result unused [-Wunused-value]
dynamic_cast<B4*>(v); // well-defined: v of type V4*, V4 base of B4
^~~~~~~~~~~~~~~~~~~~
p301.cpp:89:1: warning: expression result unused [-Wunused-value]
dynamic_cast<B4*>(a); // undefined behavior,
^~~~~~~~~~~~~~~~~~~~
5 warnings generated.
Undefined symbols for architecture x86_64:
  "Y::()", referenced from:
      B::() in p301-9b2046.o
  "V4::f()", referenced from:
      vtable for B4 in p301-9b2046.o
  "typeinfo for V4", referenced from:
      B4::B4(V4*, A4*) in p301-9b2046.o
      B4::B4(V4*, A4*) in p301-9b2046.o
      typeinfo for B4 in p301-9b2046.o
      typeinfo for A4 in p301-9b2046.o
  "vtable for V", referenced from:
      V::() in p301-9b2046.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for B3", referenced from:
      B3::B3(V*, A3*) in p301-9b2046.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for V4", referenced from:
      V4::V4() in p301-9b2046.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang-6.0: error: linker command failed with exit code 1 (use -v to see invocation)

$ g++-7 p301.cpp
Undefined symbols for architecture x86_64:
  "V::f()", referenced from:
      B3::B3(V*, A3*)   in ccqdeMPa.o
      B3::B3(V*, A3*)   in ccqdeMPa.o
  "Y::Y()", referenced from:
      B::B()     in ccqdeMPa.o
  "B3::g()", referenced from:
      B3::B3(V*, A3*)   in ccqdeMPa.o
      B3::B3(V*, A3*)   in ccqdeMPa.o
  "V4::f()", referenced from:
      vtable for B4 in ccqdeMPa.o
  "typeinfo for V4", referenced from:
      typeinfo for B4 in ccqdeMPa.o
      typeinfo for A4 in ccqdeMPa.o
  "vtable for V", referenced from:
      V::V()     in ccqdeMPa.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for B3", referenced from:
      B3::B3(V*, A3*)   in ccqdeMPa.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for V4", referenced from:
      V4::V4()    in ccqdeMPa.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status

検討事項

リンクエラーをなくす修正
意味のある出力
clang++で警告ありg++警告なしの背景

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

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.

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