9.9 The using declaration [namespace.udecl] C++N4910:2022 (118) p232.cpp

はじめに(Introduction)

N4910 Working Draft, Standard for Programming Language C++

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

C++N4741, 2018 Standard Working Draft on ISO/IEC 14882 sample code compile list

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++

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.

9.9 The using declaration [namespace.udecl] C++N4910:2022 (118) p232.cpp

算譜(source code)

p232.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 = "9.9 The using declaration [namespace.udecl] C++N4910:2022 (118) p232.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>

using namespace std;

// Example 1
enum class button { up, down };
struct S {
    using button::up;
    button b = up; // OK
};
// [Example 2 :
struct B {
    void f(char);
    enum E { e };
    union {
        int x;
    };
};
struct C {
    int f();
};
struct D : B {
    using B::f; // OK, B is a base of D
    using B::e; // OK, e is an enumerator of base B
    using B::x; // OK, x is a union member of base B
    using C::f; // error: C isn’t a base of D
    void f(int) {
        f('c');    // calls B::f(char)
    }
    void g(int) {
        g('c');    // recursively calls D::g(int)
    }
};
template <typename... bases>
struct X : bases... {
    using bases::f...;
};
X<B, C> x; // OK, B::f and C::f named
// [Example 3 :
struct A3 {
    template <class T> void f3(T);
    template <class T> struct X3 { };
};
struct B3 : A3 {
    using A3::f3<double>; // error
    using A3::X3<int>; // error
};
// [Example 4 :
struct X4 {
    int i4;
    static int s4;
};
void f4() {
    using X4::i4; // error: X::i is a class member and this is not a member declaration.
    using X4::s4; // error: X::s is a class member and this is not a member declaration.
}
// [Example 5 :
namespace A5 {
void f5(int);
}
using A5::f5; // f is a synonym for A::f; that is, for A::f(int).
namespace A5 {
void f5(char);
}
void foo() {
    f5('a'); // calls f(int), even though f(char) exists.
}
void bar() {
    using A5::f5; // f is a synonym for A::f; that is, for A::f(int) and A::f(char).
    f5('a'); // calls f(char)
}
// [Example 6 :
namespace A6 {
int x6;
int f6(int);
int g6;
void h6();
}
namespace B6 {
int i6;
struct g6 { };
struct x6 { };
void f6(int);
void f6(double);
void g6(char); // OK, hides struct g
}
void func() {
    int i6;
    using B6::i6; // error: conflicts
    void f6(char);
    using B6::f6; // OK, each f is a function
    using A6::f6; // OK, but interferes with B::f(int)
    f6(1); // error: ambiguous
    static_cast<int(*)(int)>(f6)(1); // OK, calls A::f
    f6(3.5); // calls B::f(double)
    using B6::g6;
    g6('a'); // calls B::g(char)
    struct g6 g1; // g1 has class type B::g
    using A6::g6; // error: conflicts with B::g
    void h6();
    using A6::h6; // error: conflicts
    using B6::x6;
    using A6::x6; // OK, hides struct B::x
    x6 = 99; // assigns to A::x
    struct x6 x1; // x1 has class type B::x
}
// [Example 7 :
struct B7 {
    virtual void f7(int);
    virtual void f7(char);
    void g7(int);
    void h7(int);
};
struct D7 : B7 {
    using B7::f7;
    void f7(int); // OK, D::f(int) overrides B::f(int);
    using B7::g7;
    void g7(char); // OK
    using B7::h7;
    void h7(int); // OK, D::h(int) hides B::h(int)
};
void k7(D7* p)
{
    p->f7(1); // calls D::f(int)
    p->f7('a'); // calls B::f(char)
    p->g7(1); // calls B::g(int)
    p->g7('a'); // calls D::g(char)
}
struct B1 {
    B1(int);
};
struct B2 {
    B2(int);
};
struct D1 : B1, B2 {
    using B1::B1;
    using B2::B2;
};
D1 d1(0); // error: ambiguous
struct D2 : B1, B2 {
    using B1::B1;
    using B2::B2;
    D2(int); // OK, D2::D2(int) hides B1::B1(int) and B2::B2(int)
};
D2 d2(0); // calls D2::D2(int)
// [Example 8 :
struct A8 {
    int x8();
};
struct B8 : A8 { };
struct C8 : A8 {
    using A8::x8;
    int x8(int);
};
struct D8 : B8, C8 {
    using C8::x8;
    int x8(double);
};
int f8(D8* d8) {
    return d8->x8(); // error: overload resolution selects A::x, but A is an ambiguous base class
}
// [Example 9 :
class A9 {
private:
    void f9(char);
public:
    void f9(int);
protected:
    void g9();
};
class B9 : public A9 {
    using A9::f9; // error: A::f(char) is inaccessible
public:
    using A9::g9; // B::g is a public synonym for A::g
};
int main() {
    cout  <<  n4910 << endl;
    return EXIT_SUCCESS;
}

Script

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)

bash

# ./clgc.sh  p232
rm: cannot remove 'p232l': No such file or directory
rm: cannot remove 'p232g': No such file or directory
$ clang++ p232.cpp -std=03 -o p232l -I. -Wall
p232.cpp:23:6: warning: scoped enumerations are a C++11 extension [-Wc++11-extensions]
enum class button { up, down };
     ^
p232.cpp:25:7: warning: use of enumeration in a nested name specifier is a C++11 extension [-Wc++11-extensions]
using button::up;
      ^
p232.cpp:25:7: warning: using declaration naming a scoped enumerator is a C++20 extension [-Wc++20-extensions]
using button::up;
      ^~~~~~~~
p232.cpp:25:7: error: using declaration in class refers into 'button::', which is not a class
using button::up;
      ^~~~~~~~
p232.cpp:26:10: warning: default member initializer for non-static data member is a C++11 extension [-Wc++11-extensions]
button b = up; // OK
         ^
p232.cpp:26:12: error: use of undeclared identifier 'up'
button b = up; // OK
           ^
p232.cpp:41:7: error: using declaration refers into 'C::', which is not a base class of 'D'
using C::f; // error: C isn’t a base of D
      ^~~
p232.cpp:45:19: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template <typename... bases>
                  ^
p232.cpp:47:18: warning: pack expansion of using declaration is a C++17 extension [-Wc++17-extensions]
using bases::f...;
                 ^
p232.cpp:56:11: error: using declaration cannot refer to a template specialization
using A3::f3<double>; // error
          ^ ~~~~~~~~
p232.cpp:57:11: error: using declaration cannot refer to a template specialization
using A3::X3<int>; // error
          ^ ~~~~~
p232.cpp:65:11: error: using declaration cannot refer to class member
using X4::i4; // error: X::i is a class member and this is not a member declaration.
      ~~~~^
p232.cpp:66:11: error: using declaration cannot refer to class member
using X4::s4; // error: X::s is a class member and this is not a member declaration.
      ~~~~^
p232.cpp:66:1: note: use a reference instead
using X4::s4; // error: X::s is a class member and this is not a member declaration.
^
p232.cpp:100:11: error: target of using declaration conflicts with declaration already in scope
using B6::i6; // error: conflicts
          ^
p232.cpp:91:5: note: target of using declaration
int i6;
    ^
p232.cpp:99:5: note: conflicting declaration
int i6;
    ^
p232.cpp:104:1: error: call to 'f6' is ambiguous
f6(1); // error: ambiguous
^~
p232.cpp:86:5: note: candidate function
int f6(int);
    ^
p232.cpp:94:6: note: candidate function
void f6(int);
     ^
p232.cpp:110:11: error: target of using declaration conflicts with declaration already in scope
using A6::g6; // error: conflicts with B::g
          ^
p232.cpp:87:5: note: target of using declaration
int g6;
    ^
p232.cpp:96:6: note: conflicting declaration
void g6(char); // OK, hides struct g
     ^
p232.cpp:112:11: error: target of using declaration conflicts with declaration already in scope
using A6::h6; // error: conflicts
          ^
p232.cpp:88:6: note: target of using declaration
void h6();
     ^
p232.cpp:111:6: note: conflicting declaration
void h6();
     ^
p232.cpp:147:11: error: using declaration cannot refer to a constructor
using B1::B1;
      ~~~~^
p232.cpp:148:11: error: using declaration cannot refer to a constructor
using B2::B2;
      ~~~~^
p232.cpp:150:4: error: no matching constructor for initialization of 'D1'
D1 d1(0); // error: ambiguous
   ^  ~
p232.cpp:146:8: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'int' to 'const D1' for 1st argument
struct D1 : B1, B2 {
       ^
p232.cpp:146:8: note: candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 1 was provided
p232.cpp:152:11: error: using declaration cannot refer to a constructor
using B1::B1;
      ~~~~^
p232.cpp:153:11: error: using declaration cannot refer to a constructor
using B2::B2;
      ~~~~^
p232.cpp:169:8: error: ambiguous conversion from derived class 'D8' to base class 'A8':
    struct D8 -> struct B8 -> struct A8
    struct D8 -> struct C8 -> struct A8
return d8->x8(); // error: overload resolution selects A::x, but A is an ambiguous base class
       ^~
p232.cpp:181:11: error: 'f9' is a private member of 'A9'
using A9::f9; // error: A::f(char) is inaccessible
          ^
p232.cpp:174:6: note: declared private here
void f9(char);
     ^
6 warnings and 18 errors generated.
rm: cannot remove 'p232l': No such file or directory
$ clang++ p232.cpp -std=2b -o p232l -I. -Wall
p232.cpp:41:7: error: using declaration refers into 'C::', which is not a base class of 'D'
using C::f; // error: C isn’t a base of D
      ^~~
p232.cpp:56:11: error: using declaration cannot refer to a template specialization
using A3::f3<double>; // error
          ^ ~~~~~~~~
p232.cpp:57:11: error: using declaration cannot refer to a template specialization
using A3::X3<int>; // error
          ^ ~~~~~
p232.cpp:65:11: error: using declaration cannot refer to class member
using X4::i4; // error: X::i is a class member and this is not a member declaration.
      ~~~~^
p232.cpp:66:11: error: using declaration cannot refer to class member
using X4::s4; // error: X::s is a class member and this is not a member declaration.
      ~~~~^
p232.cpp:66:1: note: use a reference instead
using X4::s4; // error: X::s is a class member and this is not a member declaration.
^~~~~
auto &s4 = 
p232.cpp:100:11: error: target of using declaration conflicts with declaration already in scope
using B6::i6; // error: conflicts
          ^
p232.cpp:91:5: note: target of using declaration
int i6;
    ^
p232.cpp:99:5: note: conflicting declaration
int i6;
    ^
p232.cpp:104:1: error: call to 'f6' is ambiguous
f6(1); // error: ambiguous
^~
p232.cpp:86:5: note: candidate function
int f6(int);
    ^
p232.cpp:94:6: note: candidate function
void f6(int);
     ^
p232.cpp:110:11: error: target of using declaration conflicts with declaration already in scope
using A6::g6; // error: conflicts with B::g
          ^
p232.cpp:87:5: note: target of using declaration
int g6;
    ^
p232.cpp:96:6: note: conflicting declaration
void g6(char); // OK, hides struct g
     ^
p232.cpp:112:11: error: target of using declaration conflicts with declaration already in scope
using A6::h6; // error: conflicts
          ^
p232.cpp:88:6: note: target of using declaration
void h6();
     ^
p232.cpp:111:6: note: conflicting declaration
void h6();
     ^
p232.cpp:150:4: error: call to constructor of 'D1' is ambiguous
D1 d1(0); // error: ambiguous
   ^  ~
p232.cpp:141:1: note: candidate inherited constructor
B1(int);
^
p232.cpp:147:11: note: constructor from base class 'B1' inherited here
using B1::B1;
          ^
p232.cpp:144:1: note: candidate inherited constructor
B2(int);
^
p232.cpp:148:11: note: constructor from base class 'B2' inherited here
using B2::B2;
          ^
p232.cpp:169:8: error: ambiguous conversion from derived class 'D8' to base class 'A8':
    struct D8 -> struct B8 -> struct A8
    struct D8 -> struct C8 -> struct A8
return d8->x8(); // error: overload resolution selects A::x, but A is an ambiguous base class
       ^~
p232.cpp:181:11: error: 'f9' is a private member of 'A9'
using A9::f9; // error: A::f(char) is inaccessible
          ^
p232.cpp:174:6: note: declared private here
void f9(char);
     ^
12 errors generated.

$ g++ p232.cpp -std=03 -o p232g -I. -Wall
p232.cpp:23:1: warning: scoped enums only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   23 | enum class button { up, down };
      | ^~~~
p232.cpp:25:7: error: 'button' is not a class or namespace
   25 | using button::up;
      |       ^~~~~~
p232.cpp:26:10: warning: non-static data member initializers only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   26 | button b = up; // OK
      |          ^
p232.cpp:26:12: error: 'up' was not declared in this scope; did you mean 'button::up'?
   26 | button b = up; // OK
      |            ^~
      |            button::up
p232.cpp:23:21: note: 'button::up' declared here
   23 | enum class button { up, down };
      |                     ^~
p232.cpp:41:10: error: type 'C' is not a base type for type 'D'
   41 | using C::f; // error: C isn’t a base of D
      |          ^
p232.cpp:45:19: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   45 | template <typename... bases>
      |                   ^~~
p232.cpp:47:15: warning: pack expansion in using-declaration only available with '-std=c++17' or '-std=gnu++17' [-Wc++17-extensions]
   47 | using bases::f...;
      |               ^~~
p232.cpp:56:11: error: a template-id may not appear in a using-declaration
   56 | using A3::f3<double>; // error
      |           ^~~~~~~~~~
p232.cpp:57:11: error: a template-id may not appear in a using-declaration
   57 | using A3::X3<int>; // error
      |           ^~~~~~~
p232.cpp: In function 'void f4()':
p232.cpp:65:11: error: using-declaration for member at non-class scope
   65 | using X4::i4; // error: X::i is a class member and this is not a member declaration.
      |           ^~
p232.cpp:66:11: error: using-declaration for member at non-class scope
   66 | using X4::s4; // error: X::s is a class member and this is not a member declaration.
      |           ^~
p232.cpp: In function 'void func()':
p232.cpp:100:11: error: 'int B6::i6' conflicts with a previous declaration
  100 | using B6::i6; // error: conflicts
      |           ^~
p232.cpp:99:5: note: previous declaration 'int i6'
   99 | int i6;
      |     ^~
p232.cpp:104:3: error: call of overloaded 'f6(int)' is ambiguous
  104 | f6(1); // error: ambiguous
      | ~~^~~
p232.cpp:101:6: note: candidate: 'void f6(char)'
  101 | void f6(char);
      |      ^~
p232.cpp:95:6: note: candidate: 'void B6::f6(double)'
   95 | void f6(double);
      |      ^~
p232.cpp:94:6: note: candidate: 'void B6::f6(int)'
   94 | void f6(int);
      |      ^~
p232.cpp:86:5: note: candidate: 'int A6::f6(int)'
   86 | int f6(int);
      |     ^~
p232.cpp:110:11: error: 'int A6::g6' conflicts with a previous declaration
  110 | using A6::g6; // error: conflicts with B::g
      |           ^~
p232.cpp:96:6: note: previous declaration 'void B6::g6(char)'
   96 | void g6(char); // OK, hides struct g
      |      ^~
p232.cpp:112:11: error: 'void A6::h6()' conflicts with a previous declaration
  112 | using A6::h6; // error: conflicts
      |           ^~
p232.cpp:111:6: note: previous declaration 'void h6()'
  111 | void h6();
      |      ^~
p232.cpp:99:5: warning: unused variable 'i6' [-Wunused-variable]
   99 | int i6;
      |     ^~
p232.cpp:109:11: warning: unused variable 'g1' [-Wunused-variable]
  109 | struct g6 g1; // g1 has class type B::g
      |           ^~
p232.cpp:116:11: warning: unused variable 'x1' [-Wunused-variable]
  116 | struct x6 x1; // x1 has class type B::x
      |           ^~
p232.cpp: At global scope:
p232.cpp:147:11: warning: inheriting constructors only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
  147 | using B1::B1;
      |           ^~
p232.cpp:148:11: warning: inheriting constructors only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
  148 | using B2::B2;
      |           ^~
p232.cpp:150:8: error: call of overloaded 'D1(int)' is ambiguous
  150 | D1 d1(0); // error: ambiguous
      |        ^
p232.cpp:144:1: note: candidate: 'B2::B2(int)'
  144 | B2(int);
      | ^~
p232.cpp:148:11: note:   inherited here
  148 | using B2::B2;
      |           ^~
p232.cpp:141:1: note: candidate: 'B1::B1(int)'
  141 | B1(int);
      | ^~
p232.cpp:147:11: note:   inherited here
  147 | using B1::B1;
      |           ^~
p232.cpp:146:8: note: candidate: 'D1::D1(const D1&)'
  146 | struct D1 : B1, B2 {
      |        ^~
p232.cpp:152:11: warning: inheriting constructors only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
  152 | using B1::B1;
      |           ^~
p232.cpp:153:11: warning: inheriting constructors only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
  153 | using B2::B2;
      |           ^~
p232.cpp: In function 'int f8(D8*)':
p232.cpp:169:14: error: 'A8' is an ambiguous base of 'D8'
  169 | return d8->x8(); // error: overload resolution selects A::x, but A is an ambiguous base class
      |        ~~~~~~^~
p232.cpp: At global scope:
p232.cpp:181:11: error: 'void A9::f9(char)' is private within this context
  181 | using A9::f9; // error: A::f(char) is inaccessible
      |           ^~
p232.cpp:174:6: note: declared private here
  174 | void f9(char);
      |      ^~
rm: cannot remove 'p232g': No such file or directory

$ g++ p232.cpp -std=2b -o p232g -I. -Wall
p232.cpp:41:10: error: type 'C' is not a base type for type 'D'
   41 | using C::f; // error: C isn’t a base of D
      |          ^
p232.cpp:56:11: error: a template-id may not appear in a using-declaration
   56 | using A3::f3<double>; // error
      |           ^~~~~~~~~~
p232.cpp:57:11: error: a template-id may not appear in a using-declaration
   57 | using A3::X3<int>; // error
      |           ^~~~~~~
p232.cpp: In function 'void f4()':
p232.cpp:65:11: error: using-declaration for member at non-class scope
   65 | using X4::i4; // error: X::i is a class member and this is not a member declaration.
      |           ^~
p232.cpp:66:11: error: using-declaration for member at non-class scope
   66 | using X4::s4; // error: X::s is a class member and this is not a member declaration.
      |           ^~
p232.cpp: In function 'void func()':
p232.cpp:100:11: error: 'int B6::i6' conflicts with a previous declaration
  100 | using B6::i6; // error: conflicts
      |           ^~
p232.cpp:99:5: note: previous declaration 'int i6'
   99 | int i6;
      |     ^~
p232.cpp:104:3: error: call of overloaded 'f6(int)' is ambiguous
  104 | f6(1); // error: ambiguous
      | ~~^~~
p232.cpp:101:6: note: candidate: 'void f6(char)'
  101 | void f6(char);
      |      ^~
p232.cpp:95:6: note: candidate: 'void B6::f6(double)'
   95 | void f6(double);
      |      ^~
p232.cpp:94:6: note: candidate: 'void B6::f6(int)'
   94 | void f6(int);
      |      ^~
p232.cpp:86:5: note: candidate: 'int A6::f6(int)'
   86 | int f6(int);
      |     ^~
p232.cpp:110:11: error: 'int A6::g6' conflicts with a previous declaration
  110 | using A6::g6; // error: conflicts with B::g
      |           ^~
p232.cpp:96:6: note: previous declaration 'void B6::g6(char)'
   96 | void g6(char); // OK, hides struct g
      |      ^~
p232.cpp:112:11: error: 'void A6::h6()' conflicts with a previous declaration
  112 | using A6::h6; // error: conflicts
      |           ^~
p232.cpp:111:6: note: previous declaration 'void h6()'
  111 | void h6();
      |      ^~
p232.cpp:99:5: warning: unused variable 'i6' [-Wunused-variable]
   99 | int i6;
      |     ^~
p232.cpp:109:11: warning: unused variable 'g1' [-Wunused-variable]
  109 | struct g6 g1; // g1 has class type B::g
      |           ^~
p232.cpp:116:11: warning: unused variable 'x1' [-Wunused-variable]
  116 | struct x6 x1; // x1 has class type B::x
      |           ^~
p232.cpp: At global scope:
p232.cpp:150:8: error: call of overloaded 'D1(int)' is ambiguous
  150 | D1 d1(0); // error: ambiguous
      |        ^
p232.cpp:144:1: note: candidate: 'B2::B2(int)'
  144 | B2(int);
      | ^~
p232.cpp:148:11: note:   inherited here
  148 | using B2::B2;
      |           ^~
p232.cpp:141:1: note: candidate: 'B1::B1(int)'
  141 | B1(int);
      | ^~
p232.cpp:147:11: note:   inherited here
  147 | using B1::B1;
      |           ^~
p232.cpp:146:8: note: candidate: 'constexpr D1::D1(const D1&)'
  146 | struct D1 : B1, B2 {
      |        ^~
p232.cpp:146:8: note: candidate: 'constexpr D1::D1(D1&&)'
p232.cpp: In function 'int f8(D8*)':
p232.cpp:169:14: error: 'A8' is an ambiguous base of 'D8'
  169 | return d8->x8(); // error: overload resolution selects A::x, but A is an ambiguous base class
      |        ~~~~~~^~
p232.cpp: At global scope:
p232.cpp:181:11: error: 'void A9::f9(char)' is private within this context
  181 | using A9::f9; // error: A::f(char) is inaccessible
      |           ^~
p232.cpp:174:6: note: declared private here
  174 | void f9(char);
      |      ^~

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。-->

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＜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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