11.7.3 Virtual functions [class.virtual] C++N4910:2022 (160) p290.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.

# 11.7.3 Virtual functions [class.virtual] C++N4910:2022 (160) p290.cpp

## 算譜(source code)

```c++:p290.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 = "11.7.3 Virtual functions [class.virtual] C++N4910:2022 (160) p290.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 {
    virtual void f();
};
struct B : virtual A {
    virtual void f();
};
struct C : B, virtual A {
    using A::f;
};
void foo() {
    C c;
    c.f(); // calls B::f, the final overrider
    c.C::f(); // calls A::f because of the using-declaration }
// [Example 2:
    struct A2 {
        virtual void f();
    };
    struct B2 : A2 { };
    struct C2 : A2 {
        void f();
    };
    struct D2 : B2, C2 { }; // OK, A::f and C::f are the final overriders
// for the B and C subobjects, respectively
// [Note 2: A virtual member function does not have to be visible to be overridden, for example,
    struct BN {
        virtual void f();
    };
    struct DN : BN {
        void f(int);
    };
    struct D2N : DN {
        void f();
    };
//the function f(int) in class D hides the virtual function f() in its base class B; D::f(int) is not a virtual function. However, f() declared in class D2 has the same name and the same parameter list as B::f(), and therefore is a virtual function that overrides the function B::f() even though B::f() is not visible in class D2.
// [Example 3:
    struct B3 {
        virtual void f3() const final;
    };
    struct D3 : B3 {
        void f3() const; // error: D::f attempts to override final B::f
    };
// [Example 4:
    struct B4 {
        virtual void f4(int);
    };
    struct D4 : B4 {
        virtual void
        virtual void
    };
    f4(long) override;
    f4(int) override;
// error: wrong signature overriding B::f // OK
// [Example 5:
    template<typename T>
    struct A5 {
        virtual void f() requires true;
    };
// [Example 6:
    class B6 { };
    class D6 : private B6 {
        friend class Derived;
    };
    struct Base {
        virtual void vf1();
        virtual void vf2();
        virtual void vf3();
        virtual B6*   vf4();
        virtual B6*   vf5();
        void f6();
    };
    struct No_good : public Base {
        D* vf4(); // error: B (base class of D) inaccessible
    };
    class A6;
    struct Derived : public Base {
        void vf1();
        void vf2(int);
        char vf3();
        D6*   vf4();
        A6*   vf5();
        void f6();
    };
    void g6() {
        Derived d;
        Base* bp = &d;
// virtual and overrides Base::vf1()
// not virtual, hides Base::vf2()
// error: invalid difference in return type only // OK, returns pointer to derived class
// error: returns pointer to incomplete class
// standard conversion:
// [Example 7: Here are some uses of virtual functions with multiple base classes:
    }
// In class D above there are two occurrences of class A and hence two occurrences of the virtual member function A::f. The final overrider of B1::A::f is B1::f and the final overrider of B2::A::f is B2::f.
// [Example 8: The following example shows a function that does not have a unique final overrider:
    bp->vf1();
    bp->vf2();
    bp->f8();
    B8*  p = bp->vf4();
    Derived*  dp = &d;
    D8*  q = dp->vf4();
    dp->vf2();
// cal ls
// cal ls
// cal ls
// cal ls
// result to B*
}
struct A8 {
    virtual void f8();
};
struct B18 : A8 {
    void f8();
};
struct B28 : A8 {
    void f8();
};
struct D8 : B18, B28 {
};
void foo8() {
    D8   d8;
// note non-virtual derivation
// D has two separate A subobjects
// A* ap = &d; // would be ill-formed: ambiguous B1* b1p = &d;
    A8* ap = b1p;
    D8* dp = &d;
    ap->f8();
    dp->f8();
};
// calls D::B1::f // error: ambiguous
struct A81 {
    virtual void f8();
};
struct VB1 : virtual A81 {
    void f8();
};
struct VB2 : virtual A81 {
    void f8();
};
// note virtual derivation
// Derived* to Base*
Derived::vf1()
Base::vf2()
Base::f8() (not virtual) Derived::vf4() and converts the
// cal ls Derived::vf4() and does not // convert the result to B*
// error: argument mismatch
struct Error : VB1, VB2 {
};
struct Okay : VB1, VB2 {
    void f8();
// error
};
// Both VB1::f and VB2::f override A::f but there is no overrider of both of them in class Error. This example is therefore ill-formed. Class Okay is well-formed, however, because Okay::f is a final overrider.
// [Example 9: The following example uses the well-formed classes from above.
struct VB1a : virtual A9 {
};
struct Da : VB1a, VB2 {
};
void foe() {
    VB1a*  vb1ap = new Da;
    vb1ap->f9();
}
// does not declare f
// calls VB2::f
// [Example 10:
class B9 {
public:
    virtual void f9();
};
class D9 : public B9 {
public:
    void f9();
};
void D9::f9() {
    /* ... */ B9::f9();
}
// Here, the function call in D::f really does call B::f and not D::f.
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  p290
rm: cannot remove 'p290l': No such file or directory
rm: cannot remove 'p290g': No such file or directory
$ clang++ p290.cpp -std=c++03 -o p290l -I. -Wall
In file included from p290.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 \
 ^
p290.cpp:49:13: warning: 'foo()::DN::f' hides overloaded virtual function [-Woverloaded-virtual]
       void f(int);
            ^
p290.cpp:46:21: note: hidden overloaded virtual function 'foo()::BN::f' declared here: different number of parameters (0 vs 1)
       virtual void f();
                    ^
p290.cpp:57:32: warning: 'final' keyword is a C++11 extension [-Wc++11-extensions]
       virtual void f3() const final;
                               ^
p290.cpp:60:6: error: declaration of 'f3' overrides a 'final' function
void f3() const; // error: D::f attempts to override final B::f
     ^
p290.cpp:57:21: note: overridden virtual function is here
       virtual void f3() const final;
                    ^
p290.cpp:68:3: warning: duplicate 'virtual' declaration specifier [-Wduplicate-decl-specifier]
  virtual void
  ^
p290.cpp:68:11: error: cannot combine with previous 'void' declaration specifier
  virtual void
          ^
p290.cpp:69:1: error: expected member name or ';' after declaration specifiers
};
^
p290.cpp:70:8: error: expected '(' for function-style cast or type construction
f4(long) override;
   ~~~~^
p290.cpp:71:7: error: expected '(' for function-style cast or type construction
f4(int) override;
   ~~~^
p290.cpp:74:3: error: expected expression
  template<typename T>
  ^
p290.cpp:90:1: error: unknown type name 'D'
D* vf4(); // error: B (base class of D) inaccessible
^
p290.cpp:96:10: error: virtual function 'vf3' has a different return type ('char') than the function it overrides (which has return type 'void')
    char vf3();
    ~~~~ ^
p290.cpp:84:21: note: overridden virtual function is here
       virtual void vf3();
               ~~~~ ^
p290.cpp:97:11: error: invalid covariant return for virtual function: 'B6' is a private base class of 'D6'
    D6*   vf4();
          ^
p290.cpp:80:17: note: declared private here
     class D6 : private B6 { friend class Derived; };
                ^~~~~~~~~~
p290.cpp:98:11: error: return type of virtual function 'vf5' is not covariant with the return type of the function it overrides ('A6' is incomplete)
    A6*   vf5();
          ^
p290.cpp:92:12: note: forward declaration of 'A6'
     class A6;
           ^
p290.cpp:95:10: warning: 'foo()::Derived::vf2' hides overloaded virtual function [-Woverloaded-virtual]
    void vf2(int);
         ^
p290.cpp:83:21: note: hidden overloaded virtual function 'foo()::Base::vf2' declared here: different number of parameters (0 vs 1)
       virtual void vf2();
                    ^
p290.cpp:101:11: error: function definition is not allowed here
void g6() {
          ^
p290.cpp:113:5: error: use of undeclared identifier 'bp'
    bp->vf1();
    ^
p290.cpp:114:5: error: use of undeclared identifier 'bp'
    bp->vf2();
    ^
p290.cpp:115:5: error: use of undeclared identifier 'bp'
    bp->f8();
    ^
p290.cpp:116:5: error: unknown type name 'B8'
    B8*  p = bp->vf4();
    ^
p290.cpp:116:14: error: use of undeclared identifier 'bp'
    B8*  p = bp->vf4();
             ^
p290.cpp:117:21: error: use of undeclared identifier 'd'
    Derived*  dp = &d;
                    ^
p290.cpp:118:5: error: unknown type name 'D8'
    D8*  q = dp->vf4();
    ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
4 warnings and 20 errors generated.
rm: cannot remove 'p290l': No such file or directory
$ clang++ p290.cpp -std=c++2b -o p290l -I. -Wall
p290.cpp:49:13: warning: 'foo()::DN::f' hides overloaded virtual function [-Woverloaded-virtual]
       void f(int);
            ^
p290.cpp:46:21: note: hidden overloaded virtual function 'foo()::BN::f' declared here: different number of parameters (0 vs 1)
       virtual void f();
                    ^
p290.cpp:60:6: error: declaration of 'f3' overrides a 'final' function
void f3() const; // error: D::f attempts to override final B::f
     ^
p290.cpp:57:21: note: overridden virtual function is here
       virtual void f3() const final;
                    ^
p290.cpp:68:3: warning: duplicate 'virtual' declaration specifier [-Wduplicate-decl-specifier]
  virtual void
  ^
p290.cpp:68:11: error: cannot combine with previous 'void' declaration specifier
  virtual void
          ^
p290.cpp:69:1: error: expected member name or ';' after declaration specifiers
};
^
p290.cpp:70:8: error: expected '(' for function-style cast or type construction
f4(long) override;
   ~~~~^
p290.cpp:71:7: error: expected '(' for function-style cast or type construction
f4(int) override;
   ~~~^
p290.cpp:74:3: error: expected expression
  template<typename T>
  ^
p290.cpp:90:1: error: unknown type name 'D'
D* vf4(); // error: B (base class of D) inaccessible
^
p290.cpp:96:10: error: virtual function 'vf3' has a different return type ('char') than the function it overrides (which has return type 'void')
    char vf3();
    ~~~~ ^
p290.cpp:84:21: note: overridden virtual function is here
       virtual void vf3();
               ~~~~ ^
p290.cpp:97:11: error: invalid covariant return for virtual function: 'B6' is a private base class of 'D6'
    D6*   vf4();
          ^
p290.cpp:80:17: note: declared private here
     class D6 : private B6 { friend class Derived; };
                ^~~~~~~~~~
p290.cpp:98:11: error: return type of virtual function 'vf5' is not covariant with the return type of the function it overrides ('A6' is incomplete)
    A6*   vf5();
          ^
p290.cpp:92:12: note: forward declaration of 'A6'
     class A6;
           ^
p290.cpp:95:10: warning: 'foo()::Derived::vf2' hides overloaded virtual function [-Woverloaded-virtual]
    void vf2(int);
         ^
p290.cpp:83:21: note: hidden overloaded virtual function 'foo()::Base::vf2' declared here: different number of parameters (0 vs 1)
       virtual void vf2();
                    ^
p290.cpp:101:11: error: function definition is not allowed here
void g6() {
          ^
p290.cpp:113:5: error: use of undeclared identifier 'bp'
    bp->vf1();
    ^
p290.cpp:114:5: error: use of undeclared identifier 'bp'
    bp->vf2();
    ^
p290.cpp:115:5: error: use of undeclared identifier 'bp'
    bp->f8();
    ^
p290.cpp:116:5: error: unknown type name 'B8'
    B8*  p = bp->vf4();
    ^
p290.cpp:116:14: error: use of undeclared identifier 'bp'
    B8*  p = bp->vf4();
             ^
p290.cpp:117:21: error: use of undeclared identifier 'd'
    Derived*  dp = &d;
                    ^
p290.cpp:118:5: error: unknown type name 'D8'
    D8*  q = dp->vf4();
    ^
p290.cpp:119:5: error: too few arguments to function call, expected 1, have 0; did you mean 'Base::vf2'?
dp->vf2();
    ^~~
    Base::vf2
p290.cpp:83:21: note: 'Base::vf2' declared here
       virtual void vf2();
                    ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
3 warnings and 20 errors generated.

$ g++ p290.cpp -std=c++03 -o p290g -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from p290.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 \
      |  ^~~~~
p290.cpp: In function 'void foo()':
p290.cpp:57:26: warning: override controls (override/final) only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   57 |        virtual void f3() const final;
      |                          ^~~~~
p290.cpp:60:6: error: virtual function 'virtual void foo()::D3::f3() const' overriding final function
   60 | void f3() const; // error: D::f attempts to override final B::f
      |      ^~
p290.cpp:57:21: note: overridden function is 'virtual void foo()::B3::f3() const'
   57 |        virtual void f3() const final;
      |                     ^~
p290.cpp:68:3: error: duplicate 'virtual'
   68 |   virtual void
      |   ^~~~~~~
      |   -------
p290.cpp:69:1: error: expected unqualified-id before '}' token
   69 | };
      | ^
p290.cpp:70:4: error: expected primary-expression before 'long'
   70 | f4(long) override;
      |    ^~~~
p290.cpp:70:1: error: 'f4' was not declared in this scope; did you mean 'D4'?
   70 | f4(long) override;
      | ^~
      | D4
p290.cpp:71:4: error: expected primary-expression before 'int'
   71 | f4(int) override;
      |    ^~~
p290.cpp:74:3: error: a template declaration cannot appear at block scope
   74 |   template<typename T>
      |   ^~~~~~~~
p290.cpp:90:1: error: 'D' does not name a type; did you mean 'D6'?
   90 | D* vf4(); // error: B (base class of D) inaccessible
      | ^
      | D6
p290.cpp:96:10: error: conflicting return type specified for 'virtual char foo()::Derived::vf3()'
   96 |     char vf3();
      |          ^~~
p290.cpp:84:21: note: overridden function is 'virtual void foo()::Base::vf3()'
   84 |        virtual void vf3();
      |                     ^~~
p290.cpp:98:11: error: invalid covariant return type for 'virtual foo()::A6* foo()::Derived::vf5()'
   98 |     A6*   vf5();
      |           ^~~
p290.cpp:86:22: note: overridden function is 'virtual foo()::B6* foo()::Base::vf5()'
   86 |        virtual B6*   vf5();
      |                      ^~~
p290.cpp:101:11: error: a function-definition is not allowed here before '{' token
  101 | void g6() {
      |           ^
p290.cpp:113:5: error: 'bp' was not declared in this scope
  113 |     bp->vf1();
      |     ^~
p290.cpp:116:5: error: 'B8' was not declared in this scope; did you mean 'B6'?
  116 |     B8*  p = bp->vf4();
      |     ^~
      |     B6
p290.cpp:116:10: error: 'p' was not declared in this scope
  116 |     B8*  p = bp->vf4();
      |          ^
p290.cpp:117:21: error: 'd' was not declared in this scope; did you mean 'dp'?
  117 |     Derived*  dp = &d;
      |                     ^
      |                     dp
p290.cpp:118:5: error: 'D8' was not declared in this scope; did you mean 'D6'?
  118 |     D8*  q = dp->vf4();
      |     ^~
      |     D6
p290.cpp:118:10: error: 'q' was not declared in this scope
  118 |     D8*  q = dp->vf4();
      |          ^
p290.cpp:119:8: error: no matching function for call to 'foo()::Derived::vf2()'
  119 | dp->vf2();
      | ~~~~~~~^~
p290.cpp:95:10: note: candidate: 'void foo()::Derived::vf2(int)'
   95 |     void vf2(int);
      |          ^~~
p290.cpp:95:10: note:   candidate expects 1 argument, 0 provided
p290.cpp: In function 'void foo8()':
p290.cpp:142:10: error: 'b1p' was not declared in this scope
  142 | A8* ap = b1p;
      |          ^~~
p290.cpp:143:11: error: 'd' was not declared in this scope; did you mean 'dp'?
  143 | D8* dp = &d;
      |           ^
      |           dp
p290.cpp:145:5: error: request for member 'f8' is ambiguous
  145 | dp->f8();
      |     ^~
p290.cpp:127:16: note: candidates are: 'virtual void A8::f8()'
  127 |   virtual void f8();
      |                ^~
p290.cpp:133:8: note:                 'virtual void B28::f8()'
  133 |   void f8();
      |        ^~
p290.cpp:130:8: note:                 'virtual void B18::f8()'
  130 |   void f8();
      |        ^~
p290.cpp: At global scope:
p290.cpp:159:1: error: 'Derived' does not name a type
  159 | Derived::vf1()
      | ^~~~~~~
p290.cpp:172:26: error: expected class-name before '{' token
  172 | struct VB1a : virtual A9 {
      |                          ^
p290.cpp: In function 'void foe()':
p290.cpp:178:10: error: 'struct VB1a' has no member named 'f9'
  178 |   vb1ap->f9();
      |          ^~
rm: cannot remove 'p290g': No such file or directory

$ g++ p290.cpp -std=c++2b -o p290g -I. -Wall
p290.cpp: In function 'void foo()':
p290.cpp:60:6: error: virtual function 'virtual void foo()::D3::f3() const' overriding final function
   60 | void f3() const; // error: D::f attempts to override final B::f
      |      ^~
p290.cpp:57:21: note: overridden function is 'virtual void foo()::B3::f3() const'
   57 |        virtual void f3() const final;
      |                     ^~
p290.cpp:68:3: error: duplicate 'virtual'
   68 |   virtual void
      |   ^~~~~~~
      |   -------
p290.cpp:69:1: error: expected unqualified-id before '}' token
   69 | };
      | ^
p290.cpp:70:4: error: expected primary-expression before 'long'
   70 | f4(long) override;
      |    ^~~~
p290.cpp:70:1: error: 'f4' was not declared in this scope; did you mean 'D4'?
   70 | f4(long) override;
      | ^~
      | D4
p290.cpp:71:4: error: expected primary-expression before 'int'
   71 | f4(int) override;
      |    ^~~
p290.cpp:74:3: error: a template declaration cannot appear at block scope
   74 |   template<typename T>
      |   ^~~~~~~~
p290.cpp:90:1: error: 'D' does not name a type; did you mean 'D6'?
   90 | D* vf4(); // error: B (base class of D) inaccessible
      | ^
      | D6
p290.cpp:96:10: error: conflicting return type specified for 'virtual char foo()::Derived::vf3()'
   96 |     char vf3();
      |          ^~~
p290.cpp:84:21: note: overridden function is 'virtual void foo()::Base::vf3()'
   84 |        virtual void vf3();
      |                     ^~~
p290.cpp:98:11: error: invalid covariant return type for 'virtual foo()::A6* foo()::Derived::vf5()'
   98 |     A6*   vf5();
      |           ^~~
p290.cpp:86:22: note: overridden function is 'virtual foo()::B6* foo()::Base::vf5()'
   86 |        virtual B6*   vf5();
      |                      ^~~
p290.cpp:101:11: error: a function-definition is not allowed here before '{' token
  101 | void g6() {
      |           ^
p290.cpp:113:5: error: 'bp' was not declared in this scope
  113 |     bp->vf1();
      |     ^~
p290.cpp:116:5: error: 'B8' was not declared in this scope; did you mean 'B6'?
  116 |     B8*  p = bp->vf4();
      |     ^~
      |     B6
p290.cpp:116:10: error: 'p' was not declared in this scope
  116 |     B8*  p = bp->vf4();
      |          ^
p290.cpp:117:21: error: 'd' was not declared in this scope; did you mean 'dp'?
  117 |     Derived*  dp = &d;
      |                     ^
      |                     dp
p290.cpp:118:5: error: 'D8' was not declared in this scope; did you mean 'D6'?
  118 |     D8*  q = dp->vf4();
      |     ^~
      |     D6
p290.cpp:118:10: error: 'q' was not declared in this scope
  118 |     D8*  q = dp->vf4();
      |          ^
p290.cpp:119:8: error: no matching function for call to 'foo()::Derived::vf2()'
  119 | dp->vf2();
      | ~~~~~~~^~
p290.cpp:95:10: note: candidate: 'void foo()::Derived::vf2(int)'
   95 |     void vf2(int);
      |          ^~~
p290.cpp:95:10: note:   candidate expects 1 argument, 0 provided
p290.cpp: In function 'void foo8()':
p290.cpp:142:10: error: 'b1p' was not declared in this scope
  142 | A8* ap = b1p;
      |          ^~~
p290.cpp:143:11: error: 'd' was not declared in this scope; did you mean 'dp'?
  143 | D8* dp = &d;
      |           ^
      |           dp
p290.cpp:145:5: error: request for member 'f8' is ambiguous
  145 | dp->f8();
      |     ^~
p290.cpp:127:16: note: candidates are: 'virtual void A8::f8()'
  127 |   virtual void f8();
      |                ^~
p290.cpp:133:8: note:                 'virtual void B28::f8()'
  133 |   void f8();
      |        ^~
p290.cpp:130:8: note:                 'virtual void B18::f8()'
  130 |   void f8();
      |        ^~
p290.cpp: At global scope:
p290.cpp:159:1: error: 'Derived' does not name a type
  159 | Derived::vf1()
      | ^~~~~~~
p290.cpp:172:26: error: expected class-name before '{' token
  172 | struct VB1a : virtual A9 {
      |                          ^
p290.cpp: In function 'void foe()':
p290.cpp:178:10: error: 'struct VB1a' has no member named 'f9'
  178 |   vb1ap->f9();
      |          ^~

```

## 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)
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