14.5 Exception specifications [except.spec] C++N4910:2022 (248) p444.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.

# 14.5 Exception specifications [except.spec] C++N4910:2022 (248) p444.cpp

## 算譜(source code)

```c++:p444.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 = "14.5 Exception specifications [except.spec] C++N4910:2022 (248) p444.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>
#include <typeinfo>

using namespace std;

// Example 1
void f() noexcept(sizeof(char[2])); // error: narrowing conversion of value 2 to type bool
void g() noexcept(sizeof(char)); // OK, conversion of value 1 to type bool is non-narrowing
// [Example 2:
struct B {
    virtual void f2() noexcept;
    virtual void g2();
    virtual void h() noexcept = delete;
};
struct D: B {
    void f2();
    void g2() noexcept;
    void h() = delete;
// error // OK // OK
};
// The declaration of D::f is ill-formed because it has a potentially-throwing exception specification, whereas B::f has a non-throwing exception specification.
// [Example 3:
extern void f3(); // potentially-throwing
void g3() noexcept {
    f3();
// valid, even if f throws
// valid, effectively a call to std::terminate
    throw 42;
// The call to f is well-formed even though, when called, f might throw an exception.
}
// [Example 4 :
struct A4 {
    A4(int = (A4(5), 0)) noexcept;
    A4(const A4&) noexcept;
    A4(A4&&) noexcept;
    ~A4();
};
struct B4 {
    B4() noexcept;
    B4(const B4&) = default;
    B4(B4&&, int = (throw 42, 0)) noexcept;
    ~B4() noexcept(false);
};
int n = 7;
// implicit exception specification is noexcept(true)
struct D4 : public A4, public B4 {
    int * p = new int[n];
// D::D() potentially-throwing, as the new operator may throw bad_alloc or bad_array_new_length
// // D::D(const D&) non-throwing
// D::D(D&&) potentially-throwing, as the default argument for B’s constructor may throw
// D::~D() potentially-throwing
};
// Furthermore, if A::~A() were virtual, the program would be ill-formed since a function that overrides a virtual function from a base class shall not have a potentially-throwing exception specification if the base class function has a non-throwing exception specification.
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 p444
$ clang++ p444.cpp -std=c++03 -o p444l -I. -Wall
In file included from p444.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 \
 ^
p444.cpp:26:10: error: expected function body after function declarator
void f() noexcept(sizeof(char[2])); // error: narrowing conversion of value 2 to type bool
         ^
p444.cpp:27:10: error: expected function body after function declarator
void g() noexcept(sizeof(char)); // OK, conversion of value 1 to type bool is non-narrowing 
         ^
p444.cpp:30:25: error: expected ';' at end of declaration list
       virtual void f2() noexcept;
                        ^
                        ;
p444.cpp:32:24: error: expected ';' at end of declaration list
       virtual void h() noexcept = delete;
                       ^
                       ;
p444.cpp:36:12: error: expected ';' at end of declaration list
  void g2() noexcept;
           ^
           ;
p444.cpp:37:14: warning: deleted function definitions are a C++11 extension [-Wc++11-extensions]
  void h() = delete;
             ^
p444.cpp:37:8: error: deleted function 'h' cannot override a non-deleted function
  void h() = delete;
       ^
p444.cpp:32:21: note: overridden virtual function is here
       virtual void h() noexcept = delete;
                    ^
p444.cpp:43:11: error: expected function body after function declarator
void g3() noexcept {
          ^
p444.cpp:57:5: error: expected ';' at end of declaration list
B4() noexcept;
    ^
    ;
p444.cpp:58:17: warning: defaulted function definitions are a C++11 extension [-Wc++11-extensions]
B4(const B4&) = default;
                ^
p444.cpp:59:6: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
     ^
p444.cpp:59:30: error: expected ';' at end of declaration list
B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
                             ^
                             ;
p444.cpp:59:46: error: expected ';' at end of declaration list
B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
                                             ^
                                             ;
p444.cpp:63:20: error: expected class name
struct D4 : public A4, public B4 {
                   ^
p444.cpp:64:9: warning: default member initializer for non-static data member is a C++11 extension [-Wc++11-extensions]
int * p = new int[n];
        ^
4 warnings and 12 errors generated.
rm: cannot remove 'p444l': No such file or directory
$ clang++ p444.cpp -std=c++2b -o p444l -I. -Wall
p444.cpp:26:19: error: noexcept specifier argument evaluates to 2, which cannot be narrowed to type 'bool' [-Wc++11-narrowing]
void f() noexcept(sizeof(char[2])); // error: narrowing conversion of value 2 to type bool
                  ^
p444.cpp:35:8: error: exception specification of overriding function is more lax than base version
  void f2();
       ^
p444.cpp:30:21: note: overridden virtual function is here
       virtual void f2() noexcept;
                    ^
p444.cpp:37:8: error: exception specification of overriding function is more lax than base version
  void h() = delete;
       ^
p444.cpp:32:21: note: overridden virtual function is here
       virtual void h() noexcept = delete;
                    ^
3 errors generated.

$ g++ p444.cpp -std=c++03 -o p444g -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from p444.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 \
      |  ^~~~~
p444.cpp:26:10: warning: identifier 'noexcept' is a keyword in C++11 [-Wc++11-compat]
   26 | void f() noexcept(sizeof(char[2])); // error: narrowing conversion of value 2 to type bool
      |          ^~~~~~~~
p444.cpp:26:10: error: expected initializer before 'noexcept'
p444.cpp:27:10: error: expected initializer before 'noexcept'
   27 | void g() noexcept(sizeof(char)); // OK, conversion of value 1 to type bool is non-narrowing
      |          ^~~~~~~~
p444.cpp:30:24: error: expected ';' at end of member declaration
   30 |        virtual void f2() noexcept;
      |                        ^
      |                         ;
p444.cpp:30:26: error: 'noexcept' does not name a type
   30 |        virtual void f2() noexcept;
      |                          ^~~~~~~~
p444.cpp:30:26: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:32:23: error: expected ';' at end of member declaration
   32 |        virtual void h() noexcept = delete;
      |                       ^
      |                        ;
p444.cpp:32:25: error: 'noexcept' does not name a type
   32 |        virtual void h() noexcept = delete;
      |                         ^~~~~~~~
p444.cpp:32:25: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:36:11: error: expected ';' at end of member declaration
   36 |   void g2() noexcept;
      |           ^
      |            ;
p444.cpp:36:13: error: 'noexcept' does not name a type
   36 |   void g2() noexcept;
      |             ^~~~~~~~
p444.cpp:36:13: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:37:14: warning: defaulted and deleted functions only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   37 |   void h() = delete;
      |              ^~~~~~
p444.cpp:37:8: error: deleted function 'virtual void D::h()' overriding non-deleted function
   37 |   void h() = delete;
      |        ^
p444.cpp:32:21: note: overridden function is 'virtual void B::h()'
   32 |        virtual void h() noexcept = delete;
      |                     ^
p444.cpp:43:11: error: expected initializer before 'noexcept'
   43 | void g3() noexcept {
      |           ^~~~~~~~
p444.cpp:52:20: error: expected ';' at end of member declaration
   52 | A4(int = (A4(5), 0)) noexcept; A4(const A4&) noexcept;
      |                    ^
      |                     ;
p444.cpp:52:22: error: 'noexcept' does not name a type
   52 | A4(int = (A4(5), 0)) noexcept; A4(const A4&) noexcept;
      |                      ^~~~~~~~
p444.cpp:52:22: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:52:44: error: expected ';' at end of member declaration
   52 | A4(int = (A4(5), 0)) noexcept; A4(const A4&) noexcept;
      |                                            ^
      |                                             ;
p444.cpp:52:46: error: 'noexcept' does not name a type
   52 | A4(int = (A4(5), 0)) noexcept; A4(const A4&) noexcept;
      |                                              ^~~~~~~~
p444.cpp:52:46: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:53:6: error: expected ',' or '...' before '&&' token
   53 | A4(A4&&) noexcept;
      |      ^~
p444.cpp:53:1: error: invalid constructor; you probably meant 'A4 (const A4&)'
   53 | A4(A4&&) noexcept;
      | ^~
p444.cpp:53:8: error: expected ';' at end of member declaration
   53 | A4(A4&&) noexcept;
      |        ^
      |         ;
p444.cpp:53:10: error: 'noexcept' does not name a type
   53 | A4(A4&&) noexcept;
      |          ^~~~~~~~
p444.cpp:53:10: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:57:4: error: expected ';' at end of member declaration
   57 | B4() noexcept;
      |    ^
      |     ;
p444.cpp:57:6: error: 'noexcept' does not name a type
   57 | B4() noexcept;
      |      ^~~~~~~~
p444.cpp:57:6: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:58:17: warning: defaulted and deleted functions only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   58 | B4(const B4&) = default;
      |                 ^~~~~~~
p444.cpp:59:6: error: expected ',' or '...' before '&&' token
   59 | B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
      |      ^~
p444.cpp:59:1: error: invalid constructor; you probably meant 'B4 (const B4&)'
   59 | B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
      | ^~
p444.cpp:59:29: error: expected ';' at end of member declaration
   59 | B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
      |                             ^
      |                              ;
p444.cpp:59:31: error: 'noexcept' does not name a type
   59 | B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
      |                               ^~~~~~~~
p444.cpp:59:31: note: C++11 'noexcept' only available with '-std=c++11' or '-std=gnu++11'
p444.cpp:59:45: error: expected ';' at end of member declaration
   59 | B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
      |                                             ^
      |                                              ;
p444.cpp:59:56: error: expected identifier before 'false'
   59 | B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
      |                                                        ^~~~~
p444.cpp:59:56: error: expected ',' or '...' before 'false'
p444.cpp:59:47: error: ISO C++ forbids declaration of 'noexcept' with no type [-fpermissive]
   59 | B4(B4&&, int = (throw 42, 0)) noexcept; ~B4() noexcept(false);
      |                                               ^~~~~~~~
p444.cpp:64:9: warning: non-static data member initializers only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   64 | int * p = new int[n];
      |         ^
rm: cannot remove 'p444g': No such file or directory

$ g++ p444.cpp -std=c++2b -o p444g -I. -Wall
p444.cpp:26:34: error: narrowing conversion of '2' from 'long unsigned int' to 'bool' [-Wnarrowing]
   26 | void f() noexcept(sizeof(char[2])); // error: narrowing conversion of value 2 to type bool
      |                                  ^
p444.cpp:35:8: error: looser exception specification on overriding virtual function 'virtual void D::f2()'
   35 |   void f2();
      |        ^~
p444.cpp:30:21: note: overridden function is 'virtual void B::f2() noexcept'
   30 |        virtual void f2() noexcept;
      |                     ^~
p444.cpp:37:8: error: looser exception specification on overriding virtual function 'virtual void D::h()'
   37 |   void h() = delete;
      |        ^
p444.cpp:32:21: note: overridden function is 'virtual void B::h() noexcept'
   32 |        virtual void h() noexcept = delete;
      |                     ^
p444.cpp: In function 'void g3()':
p444.cpp:47:1: warning: 'throw' will always call 'terminate' [-Wterminate]
   47 | throw 42;
      | ^~~~~~~~

```

## 検討事項(agenda)
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。

<!-- リンクエラーの解説をする。clang++とg++の比較。意味のある出力。
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)

コピペコンパイルエラーあるある

https://qiita.com/kaizen_nagoya/items/29c832de9d762aed2761

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 　20220707