11.9.3 Initializing bases and members [class.base.init] C++N4910:2022 (171) p306.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。

 <この項は書きかけです。順次追記します。>

## 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.

# 11.9.3 Initializing bases and members [class.base.init] C++N4910:2022 (171) p306.cpp

## 算譜(source code)

```c++:p306.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 * n4910 = "11.9.3 Initializing bases and members [class.base.init] C++N4910:2022 (171) p306.cpp";
// Debian clang version 14.0.5-++20220610033153+c12386ae247c-
// g++ (GCC) 12.1.0 Copyright (C) 2022 Free Software Foundation, Inc.
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.
// C++N4910:2022 Standard Working Draft on ISO/IEC 14882(0) sample code compile list
// https://qiita.com/kaizen_nagoya/items/fc957ddddd402004bb91

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <coroutine>
#include <vector>
#include <complex>
#include <map>
#include <atomic>
#include <unordered_map>

using namespace std;

// Example 1
struct A {
    A();
};
typedef A global_A;
struct B { };
struct C: public A, public B {
    C();
};
C::C(): global_A() { } // mem-initializer for base A
// [Example 2:
struct A2 {
    A2();
};
struct B22: public virtual A2 { };
struct C2: public A2, public B22 {
    C2();
};
C2::C2(): A2() { } // error: which A?
// [Example 3:
struct C3 {
    C3( int ) { } // #1: non-delegating constructor § 11.9.3
    C3(): C(42) { }
    C3( char c ) : C3(42.0) { }
    C3( double d ) : C3('a') { }
// #2: delegates to #1
// #3: ill-formed due to recursion with #4 // #4: ill-formed due to recursion with #3
};
// [Example 4:
struct B1 {
    B1(int); /* ... */
};
struct B2 {
    B2(int); /* ... */
};
struct D : B1, B2 {
    D(int);
    B1 b;
    const int c;
};
D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
D d(10);
// [Example 5:
struct A5 {
    A5() : v(42) { }
    const int& v;
};
// [Example 6:
struct A6 {
    A6();
};
struct B6 {
    B6(int);
};
struct C6 {
    C6() { }
    A6 a;
    const B6 b;
    int i;
    int j = 5;
};
// [Example 7: Given
struct A7 {
    int i = /* some integer expression with side effects */ i++ ;
    A7(int arg) : i(arg) { }
// ...
};
// the A(int) constructor will simply initialize i to the value of arg, and the side effects in is default member initializer will not take place.
// [Example 8:
struct A8 {
    A8() = default;
    A8(int v):v(v) {} const int & v = 42;
};
A8 a1;
A8 a2(1);
// OK // OK // OK
// error: ill-formed binding of temporary to reference // OK, unfortunately
// [Example 9 :
struct V {
    V();
// [Note 6: The declaration order is mandated to ensure that base and member subobjects are destroyed in the reverse
    V(int);
};
struct A9 : virtual V {
    A9();
    A9(int);
};
struct B9 : virtual V {
    B9();
    B9(int);
};
struct C9 : A9, B9, virtual V {
    C9();
    C9(int);
};
A9::A9(int i) : V(i) { /* ... */ }
B9::B9(int i) { /* ... */ }
C9::C9(int i) { /* ... */ }
V v(1);
A9 a(2);
B9 b(3);
C9 c(4);
// use V(int) // use V(int) // use V()
// use V()
// [Example 10:
class X {
    int a;
    int b;
    int i;
    int j;
public:
    const int & r;
    X(int i): r(a), b(i), i(i), j(this->i) { }
};
// initializes X::r to refer to X::a, initializes X::b with the value of the constructor parameter i, initializes X::i with the value of the constructor parameter i, and initializes X::j with the value of X::i; this takes place each time an object of class X is created.
// [Example 11:
class AB {
public:
    AB(int);
};
class BB : public AB {
    int j;
public:
    int fB();
    BB() : AB(fB()),
        j(fB()) { }
};
// undefined behavior: calls member function but base A not yet initialized // well-defined: bases are all initialized
class CB {
public:
    CB(int);
};
class DB : public BB, CB {
    int iB;
public:
    DB() : CB(fB()),
        iB(fB()) { }
};
// undefined behavior: calls member function but base C not yet initialized // well-defined: bases are all initialized
// [Example 12:
template<class... Mixins>
class XC : public Mixins... {
public:
    XC(const Mixins&... mixins) : Mixins(mixins)... { }
    };
int main() {
    cout  <<  n4910 << 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)

```ubuntu:bash
# ./clgc.sh p306
$ clang++ p306.cpp -std=c++03 -o p306l -I. -Wall
In file included from p306.cpp:19:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/atomic:38:
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/c++0x_warning.h:32:2: error: This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
#error This file requires compiler and library support \
 ^
p306.cpp:33:12: warning: direct base 'A2' is inaccessible due to ambiguity:
    struct C2 -> struct A2
    struct C2 -> struct B22 -> struct A2 [-Winaccessible-base]
struct C2: public A2, public B22 { C2(); };
           ^~~~~~~~~
p306.cpp:34:11: error: base class initializer 'A2' names both a direct base class and an inherited virtual base class
C2::C2(): A2() { } // error: which A?
          ^~
p306.cpp:38:11: error: type 'C' is not a direct or virtual base of 'C3'
    C3(): C(42) { }
          ^
p306.cpp:39:20: error: delegating constructors are permitted only in C++11
    C3( char c ) : C3(42.0) { }
                   ^~
p306.cpp:40:22: error: delegating constructors are permitted only in C++11
    C3( double d ) : C3('a') { }
                     ^~
p306.cpp:52:20: warning: initializer order does not match the declaration order [-Wreorder-ctor]
     D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
                   ^~~~~~~  ~~~~~~~  ~~~~~~  ~~~~~~
                   B1(a+2)  B2(a+1)  b(a+4)  c(a+3)
p306.cpp:52:20: note: base class 'B2' will be initialized after base 'B1'
     D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
                   ^~~~~~~
p306.cpp:52:38: note: field 'c' will be initialized after field 'b'
     D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
                                     ^~~~~~
p306.cpp:56:14: error: reference member 'v' binds to a temporary object whose lifetime would be shorter than the lifetime of the constructed object
    A5() : v(42) { }
             ^~
p306.cpp:57:16: note: reference member declared here
    const int& v;
               ^
p306.cpp:71:11: warning: default member initializer for non-static data member is a C++11 extension [-Wc++11-extensions]
    int j = 5;
          ^
p306.cpp:67:5: error: constructor for 'C6' must explicitly initialize the member 'b' which does not have a default constructor
    C6() { }
    ^
p306.cpp:69:14: note: member is declared here
    const B6 b;
             ^
p306.cpp:63:10: note: 'B6' declared here
  struct B6 {
         ^
p306.cpp:75:7: warning: default member initializer for non-static data member is a C++11 extension [-Wc++11-extensions]
int i = /* some integer expression with side effects */ i++ ; 
      ^
p306.cpp:82:8: warning: defaulted function definitions are a C++11 extension [-Wc++11-extensions]
A8() = default; 
       ^
p306.cpp:83:32: warning: default member initializer for non-static data member is a C++11 extension [-Wc++11-extensions]
A8(int v):v(v){} const int & v = 42;
                               ^
p306.cpp:83:13: warning: binding reference member 'v' to stack allocated parameter 'v' [-Wdangling-field]
A8(int v):v(v){} const int & v = 42;
            ^
p306.cpp:83:30: note: reference member declared here
A8(int v):v(v){} const int & v = 42;
                             ^
p306.cpp:82:1: error: reference member 'v' binds to a temporary object whose lifetime would be shorter than the lifetime of the constructed object
A8() = default; 
^~
p306.cpp:85:6: note: in defaulted default constructor for 'A8' first required here
  A8 a1;
     ^
p306.cpp:83:30: note: initializing field 'v' with default member initializer
A8(int v):v(v){} const int & v = 42;
                             ^   ~~
p306.cpp:120:18: warning: field 'r' will be initialized after field 'b' [-Wreorder-ctor]
       X(int i): r(a), b(i), i(i), j(this->i) { }
                 ^~~~  ~~~~  ~~~~  ~~~~~~~~~~
                 b(i)  i(i)  j(this->i) r(a)
p306.cpp:146:17: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template<class... Mixins>
                ^
p306.cpp:115:12: warning: private field 'b' is not used [-Wunused-private-field]
       int b;
           ^
p306.cpp:117:12: warning: private field 'j' is not used [-Wunused-private-field]
       int j;
           ^
11 warnings and 8 errors generated.
rm: cannot remove 'p306l': No such file or directory
$ clang++ p306.cpp -std=c++2b -o p306l -I. -Wall
p306.cpp:33:12: warning: direct base 'A2' is inaccessible due to ambiguity:
    struct C2 -> struct A2
    struct C2 -> struct B22 -> struct A2 [-Winaccessible-base]
struct C2: public A2, public B22 { C2(); };
           ^~~~~~~~~
p306.cpp:34:11: error: base class initializer 'A2' names both a direct base class and an inherited virtual base class
C2::C2(): A2() { } // error: which A?
          ^~
p306.cpp:38:11: error: type 'C' is not a direct or virtual base of 'C3'
    C3(): C(42) { }
          ^
p306.cpp:52:20: warning: initializer order does not match the declaration order [-Wreorder-ctor]
     D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
                   ^~~~~~~  ~~~~~~~  ~~~~~~  ~~~~~~
                   B1(a+2)  B2(a+1)  b(a+4)  c(a+3)
p306.cpp:52:20: note: base class 'B2' will be initialized after base 'B1'
     D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
                   ^~~~~~~
p306.cpp:52:38: note: field 'c' will be initialized after field 'b'
     D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
                                     ^~~~~~
p306.cpp:56:14: error: reference member 'v' binds to a temporary object whose lifetime would be shorter than the lifetime of the constructed object
    A5() : v(42) { }
             ^~
p306.cpp:57:16: note: reference member declared here
    const int& v;
               ^
p306.cpp:67:5: error: constructor for 'C6' must explicitly initialize the member 'b' which does not have a default constructor
    C6() { }
    ^
p306.cpp:69:14: note: member is declared here
    const B6 b;
             ^
p306.cpp:63:10: note: 'B6' declared here
  struct B6 {
         ^
p306.cpp:83:13: warning: binding reference member 'v' to stack allocated parameter 'v' [-Wdangling-field]
A8(int v):v(v){} const int & v = 42;
            ^
p306.cpp:83:30: note: reference member declared here
A8(int v):v(v){} const int & v = 42;
                             ^
p306.cpp:82:1: error: reference member 'v' binds to a temporary object whose lifetime would be shorter than the lifetime of the constructed object
A8() = default; 
^~
p306.cpp:85:6: note: in defaulted default constructor for 'A8' first required here
  A8 a1;
     ^
p306.cpp:83:30: note: initializing field 'v' with default member initializer
A8(int v):v(v){} const int & v = 42;
                             ^   ~~
p306.cpp:120:18: warning: field 'r' will be initialized after field 'b' [-Wreorder-ctor]
       X(int i): r(a), b(i), i(i), j(this->i) { }
                 ^~~~  ~~~~  ~~~~  ~~~~~~~~~~
                 b(i)  i(i)  j(this->i) r(a)
p306.cpp:40:22: error: constructor for 'C3' creates a delegation cycle [-Wdelegating-ctor-cycles]
    C3( double d ) : C3('a') { }
                     ^
p306.cpp:39:5: note: it delegates to
    C3( char c ) : C3(42.0) { }
    ^
p306.cpp:40:5: note: which delegates to
    C3( double d ) : C3('a') { }
    ^
p306.cpp:115:12: warning: private field 'b' is not used [-Wunused-private-field]
       int b;
           ^
p306.cpp:117:12: warning: private field 'j' is not used [-Wunused-private-field]
       int j;
           ^
6 warnings and 6 errors generated.

$ g++ p306.cpp -std=c++03 -o p306g -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from p306.cpp:19:
/usr/local/include/c++/12.1.0/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
   32 | #error This file requires compiler and library support \
      |  ^~~~~
p306.cpp:33:8: warning: direct base 'A2' inaccessible in 'C2' due to ambiguity [-Winaccessible-base]
   33 | struct C2: public A2, public B22 { C2(); };
      |        ^~
p306.cpp: In constructor 'C2::C2()':
p306.cpp:34:11: error: 'struct A2' is both a direct base and an indirect virtual base
   34 | C2::C2(): A2() { } // error: which A?
      |           ^~
p306.cpp: In constructor 'C3::C3()':
p306.cpp:38:11: error: type 'C' is not a direct base of 'C3'
   38 |     C3(): C(42) { }
      |           ^
p306.cpp: In constructor 'C3::C3(char)':
p306.cpp:39:27: warning: delegating constructors only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   39 |     C3( char c ) : C3(42.0) { }
      |                           ^
p306.cpp: In constructor 'C3::C3(double)':
p306.cpp:40:28: warning: delegating constructors only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   40 |     C3( double d ) : C3('a') { }
      |                            ^
p306.cpp: In constructor 'D::D(int)':
p306.cpp:52:51: warning: base 'B2' will be initialized after [-Wreorder]
   52 |      D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
      |                                                   ^
p306.cpp:52:51: warning:   base 'B1' [-Wreorder]
p306.cpp:52:6: warning:   when initialized here [-Wreorder]
   52 |      D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
      |      ^
p306.cpp:50:18: warning: 'D::c' will be initialized after [-Wreorder]
   50 |        const int c;
      |                  ^
p306.cpp:49:11: warning:   'B1 D::b' [-Wreorder]
   49 |        B1 b;
      |           ^
p306.cpp:52:6: warning:   when initialized here [-Wreorder]
   52 |      D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
      |      ^
p306.cpp: At global scope:
p306.cpp:71:11: warning: non-static data member initializers only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   71 |     int j = 5;
      |           ^
p306.cpp: In constructor 'C6::C6()':
p306.cpp:67:10: error: no matching function for call to 'B6::B6()'
   67 |     C6() { }
      |          ^
p306.cpp:64:5: note: candidate: 'B6::B6(int)'
   64 |     B6(int);
      |     ^~
p306.cpp:64:5: note:   candidate expects 1 argument, 0 provided
p306.cpp:63:10: note: candidate: 'B6::B6(const B6&)'
   63 |   struct B6 {
      |          ^~
p306.cpp:63:10: note:   candidate expects 1 argument, 0 provided
p306.cpp: At global scope:
p306.cpp:75:7: warning: non-static data member initializers only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   75 | int i = /* some integer expression with side effects */ i++ ;
      |       ^
p306.cpp:82:8: warning: defaulted and deleted functions only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   82 | A8() = default;
      |        ^~~~~~~
p306.cpp:83:32: warning: non-static data member initializers only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   83 | A8(int v):v(v){} const int & v = 42;
      |                                ^
p306.cpp:81:8: error: default member initializer for 'A8::v' required before the end of its enclosing class
   81 | struct A8 {
      |        ^~
p306.cpp:83:32: note: defined here
   83 | A8(int v):v(v){} const int & v = 42;
      |                                ^~~~~
p306.cpp: In constructor 'X::X(int)':
p306.cpp:119:20: warning: 'X::r' will be initialized after [-Wreorder]
  119 |        const int & r;
      |                    ^
p306.cpp:115:12: warning:   'int X::b' [-Wreorder]
  115 |        int b;
      |            ^
p306.cpp:120:8: warning:   when initialized here [-Wreorder]
  120 |        X(int i): r(a), b(i), i(i), j(this->i) { }
      |        ^
p306.cpp: At global scope:
p306.cpp:146:17: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
  146 |   template<class... Mixins>
      |                 ^~~
p306.cpp:149:25: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
  149 |     XC(const Mixins&... mixins) : Mixins(mixins)... { }
      |                         ^~~~~~
rm: cannot remove 'p306g': No such file or directory

$ g++ p306.cpp -std=c++2b -o p306g -I. -Wall
p306.cpp:33:8: warning: direct base 'A2' inaccessible in 'C2' due to ambiguity [-Winaccessible-base]
   33 | struct C2: public A2, public B22 { C2(); };
      |        ^~
p306.cpp: In constructor 'C2::C2()':
p306.cpp:34:11: error: 'struct A2' is both a direct base and an indirect virtual base
   34 | C2::C2(): A2() { } // error: which A?
      |           ^~
p306.cpp: In constructor 'C3::C3()':
p306.cpp:38:11: error: type 'C' is not a direct base of 'C3'
   38 |     C3(): C(42) { }
      |           ^
p306.cpp: In constructor 'D::D(int)':
p306.cpp:52:51: warning: base 'B2' will be initialized after [-Wreorder]
   52 |      D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
      |                                                   ^
p306.cpp:52:51: warning:   base 'B1' [-Wreorder]
p306.cpp:52:6: warning:   when initialized here [-Wreorder]
   52 |      D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
      |      ^
p306.cpp:50:18: warning: 'D::c' will be initialized after [-Wreorder]
   50 |        const int c;
      |                  ^
p306.cpp:49:11: warning:   'B1 D::b' [-Wreorder]
   49 |        B1 b;
      |           ^
p306.cpp:52:6: warning:   when initialized here [-Wreorder]
   52 |      D::D(int a) : B2(a+1), B1(a+2), c(a+3), b(a+4) { /* ... */ }
      |      ^
p306.cpp: In constructor 'C6::C6()':
p306.cpp:67:10: error: no matching function for call to 'B6::B6()'
   67 |     C6() { }
      |          ^
p306.cpp:64:5: note: candidate: 'B6::B6(int)'
   64 |     B6(int);
      |     ^~
p306.cpp:64:5: note:   candidate expects 1 argument, 0 provided
p306.cpp:63:10: note: candidate: 'constexpr B6::B6(const B6&)'
   63 |   struct B6 {
      |          ^~
p306.cpp:63:10: note:   candidate expects 1 argument, 0 provided
p306.cpp:63:10: note: candidate: 'constexpr B6::B6(B6&&)'
p306.cpp:63:10: note:   candidate expects 1 argument, 0 provided
p306.cpp: In constructor 'X::X(int)':
p306.cpp:119:20: warning: 'X::r' will be initialized after [-Wreorder]
  119 |        const int & r;
      |                    ^
p306.cpp:115:12: warning:   'int X::b' [-Wreorder]
  115 |        int b;
      |            ^
p306.cpp:120:8: warning:   when initialized here [-Wreorder]
  120 |        X(int i): r(a), b(i), i(i), j(this->i) { }
      |   
```

## 検討事項(agenda)
コンパイルエラーの理由を解説する。

<|--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)

cpprefjp - C++日本語リファレンス

https://cpprefjp.github.io/

コンパイラの実装状況

https://cpprefjp.github.io/implementation-status.html


typedef は C++11 ではオワコン

https://qiita.com/Linda_pp/items/44a67c64c14cba00eef1

C99からC++14を駆け抜けるC++講座

https://qiita.com/yumetodo/items/e49a673afd9a3ecb81a8

## 自己参照(self 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


clang++, g++コンパイルエラー方針の違いの例

https://qiita.com/kaizen_nagoya/items/ea6e5009fe126d270a82

astyle 使ってみた

https://qiita.com/kaizen_nagoya/items/3c9a87a781d53a1a23f3

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 <misra_c.h>
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


 ＜この記事は個人の過去の経験に基づく個人の感想です。現在所属する組織、業務とは関係がありません。＞

# 文書履歴(document history)
ver. 0.01 初稿 　20220702