Autosar Guidelines C++14, example code compile list(69)Rule A7-5-1 A function shall not return a reference or a pointer to a parameter that is passed by reference to const.

Guidelines for the use of the C++14 language in critical and
safety-related systems Sample code compile list(69)
https://www.autosar.org/fileadmin/user_upload/standards/adaptive/17-03/AUTOSAR_RS_CPP14Guidelines.pdf

Autosar Guidelines C++14 example code compile list
https://qiita.com/kaizen_nagoya/items/8ccbf6675c3494d57a76
#目的(purpose)
AutosarのC++ GuidelineをOS, 制御のプログラムで利用するにあたって、(1)hosted, freestandingのどちらを基本にすべきか。(2)C++2014,C++2017, C++202aのどれを用いると良いか, (3)どの処理系を併用すると良いかを検討するため、-std=c++14, -std=c++17, -std=c++2aの3種類で、複数のコンパイラでコンパイルすることにより、誤(error)、警告(warning)、関数・変数連携(link)、出力(output)、にどのような影響があるかを確認する。
#成果(outcome)
複数の処理系の特徴が明確になるとともに、各標準段階, hosted, freestandingの特徴と課題を明確にする。


#A7-5-1.cpp
##算譜(source code)

```c++:A7-5-1.cpp
//Guidelines for the use of the C++14 language in critical and safety-related systems
const char* msg="Rule A7-5-1 (required, implementation, automated)A function shall not return a reference or a pointer to a parameter that is passed by reference to const.(69)A7-5-1.cpp";
//https://www.autosar.org/fileadmin/user_upload/standards/adaptive/17-03/AUTOSAR_RS_CPP14Guidelines.pdf
// There is no description about Autosar declear hosted or freestanding.
// If the Autosar intended both depending on the cases, autosar.h can choose one.
// Compile with -DHOSTED work as  hosted environment, -DFREESTANDING work as freestanding.

#include "autosar.h"/// @line add header file https://qiita.com/kaizen_nagoya/items/4bde8f21ab059b96cf2a

using namespace std;/// @line add using

///start AUTOSAR: From here to the "///end AUTOSAR" is from AUTOSAR without code having /// comment in line.
// $Id: A7-5-1.cpp 271927 2017-03-24 12:01:35Z piotr.tanski $
#include <cstdint>
class A
{
public:
  explicit A(std::uint8_t n) : number(n) {}
  ~A() {
    number = 0U;
  }
// Implementation

private:
  std::uint8_t number;
};
const A& fn1(const A& ref) noexcept // Non-compliant - the function returns a
// reference to const reference parameter
// which may bind to temporary objects.
// According to C++14 Language Standard, it
// is undefined whether a temporary object is introduced for const
// reference
// parameter
{
// ...
  return ref;
}
const A& fn2(A& ref) noexcept // Compliant - non-const reference parameter does
// not bind to temporary objects, it is allowed
// that the function returns a reference to such
// a parameter
{
// ...
  return ref;
}
const A* fn3(const A& ref) noexcept // Non-compliant - the function returns a
// pointer to const reference parameter
// which may bind to temporary objects.
// According to C++14 Language Standard, it
// is undefined whether a temporary object is introduced for const
// reference
// parameter
{
// ...
  return &ref;
}
template <typename T>
T& fn4(T& v) // Compliant - the function will not bind to temporary objects
{
// ...
  return v;
}
void f() noexcept
{
  A a{5};
  const A& ref1 = fn1(a); // fn1 called with an lvalue parameter from an
// outer scope, ref1 refers to valid object
  const A& ref2 = fn2(a); // fn2 called with an lvalue parameter from an
// outer scope, ref2 refers to valid object
  const A* ptr1 = fn3(a); // fn3 called with an lvalue parameter from an
// outer scope, ptr1 refers to valid object
  const A& ref3 = fn4(a); // fn4 called with T = A, an lvalue parameter from
// an outer scope, ref3 refers to valid object

  const A& ref4 = fn1(A{10}); // fn1 called with an rvalue parameter
// (temporary), ref3 refers to destroyed object
// A const& ref5 = fn2(A{10}); // Compilation
// error - invalid initialization of non-const
// reference
  const A* ptr2 = fn3(A{15}); // fn3 called with an rvalue parameter
// (temporary), ptr2 refers to destroyted
// object
// const A& ref6 = fn4(A{20}); // Compilation error - invalid
// initialization of non-const reference
}
///end AUTOSAR
int start() { /// @{} for start
  f();
  cout<< msg << endl;
  ShutdownOS()  EXIT_SUCCESS;
/// Autosar OS 3.1.1, 2009: 7.1.2.2 Undefined Behaviour in OSEK OS
/// OS425 If ShutdownOS is called and ShutdownHook() returns then the operating system shall disable all interrupts and enter an endless loop.
}
```

##編纂・実行結果(compile and go)

```shell-session:cpa.sh
$ ../cpa.sh a7-5-1
$ clang++ a7-5-1.cpp -I./ -std=c++14 -Wall
a7-5-1.cpp:78:11: warning: unused variable 'ptr2' [-Wunused-variable]
 const A* ptr2 = fn3(A{15}); // fn3 called with an rvalue parameter
          ^
a7-5-1.cpp:64:11: warning: unused variable 'ref1' [-Wunused-variable]
 const A& ref1 = fn1(a); // fn1 called with an lvalue parameter from an
          ^
a7-5-1.cpp:68:11: warning: unused variable 'ptr1' [-Wunused-variable]
 const A* ptr1 = fn3(a); // fn3 called with an lvalue parameter from an
          ^
a7-5-1.cpp:66:11: warning: unused variable 'ref2' [-Wunused-variable]
 const A& ref2 = fn2(a); // fn2 called with an lvalue parameter from an
          ^
a7-5-1.cpp:73:11: warning: unused variable 'ref4' [-Wunused-variable]
 const A& ref4 = fn1(A{10}); // fn1 called with an rvalue parameter
          ^
a7-5-1.cpp:70:11: warning: unused variable 'ref3' [-Wunused-variable]
 const A& ref3 = fn4(a); // fn4 called with T = A, an lvalue parameter from
          ^
6 warnings generated.
Rule A7-5-1 (required, implementation, automated)A function shall not return a reference or a pointer to a parameter that is passed by reference to const.(69)A7-5-1.cpp
$ clang++ a7-5-1.cpp  -I./ -std=c++17 -Wall
a7-5-1.cpp:78:11: warning: unused variable 'ptr2' [-Wunused-variable]
 const A* ptr2 = fn3(A{15}); // fn3 called with an rvalue parameter
          ^
a7-5-1.cpp:64:11: warning: unused variable 'ref1' [-Wunused-variable]
 const A& ref1 = fn1(a); // fn1 called with an lvalue parameter from an
          ^
a7-5-1.cpp:66:11: warning: unused variable 'ref2' [-Wunused-variable]
 const A& ref2 = fn2(a); // fn2 called with an lvalue parameter from an
          ^
a7-5-1.cpp:73:11: warning: unused variable 'ref4' [-Wunused-variable]
 const A& ref4 = fn1(A{10}); // fn1 called with an rvalue parameter
          ^
a7-5-1.cpp:68:11: warning: unused variable 'ptr1' [-Wunused-variable]
 const A* ptr1 = fn3(a); // fn3 called with an lvalue parameter from an
          ^
a7-5-1.cpp:70:11: warning: unused variable 'ref3' [-Wunused-variable]
 const A& ref3 = fn4(a); // fn4 called with T = A, an lvalue parameter from
          ^
6 warnings generated.
Rule A7-5-1 (required, implementation, automated)A function shall not return a reference or a pointer to a parameter that is passed by reference to const.(69)A7-5-1.cpp
$ clang++ a7-5-1.cpp  -I./ -std=c++2a -Wall
a7-5-1.cpp:78:11: warning: unused variable 'ptr2' [-Wunused-variable]
 const A* ptr2 = fn3(A{15}); // fn3 called with an rvalue parameter
          ^
a7-5-1.cpp:70:11: warning: unused variable 'ref3' [-Wunused-variable]
 const A& ref3 = fn4(a); // fn4 called with T = A, an lvalue parameter from
          ^
a7-5-1.cpp:64:11: warning: unused variable 'ref1' [-Wunused-variable]
 const A& ref1 = fn1(a); // fn1 called with an lvalue parameter from an
          ^
a7-5-1.cpp:66:11: warning: unused variable 'ref2' [-Wunused-variable]
 const A& ref2 = fn2(a); // fn2 called with an lvalue parameter from an
          ^
a7-5-1.cpp:68:11: warning: unused variable 'ptr1' [-Wunused-variable]
 const A* ptr1 = fn3(a); // fn3 called with an lvalue parameter from an
          ^
a7-5-1.cpp:73:11: warning: unused variable 'ref4' [-Wunused-variable]
 const A& ref4 = fn1(A{10}); // fn1 called with an rvalue parameter
          ^
6 warnings generated.
Rule A7-5-1 (required, implementation, automated)A function shall not return a reference or a pointer to a parameter that is passed by reference to const.(69)A7-5-1.cpp

$ g++-8 a7-5-1.cpp  -I./ -std=c++14  -Wall
a7-5-1.cpp: In function 'void f()':
a7-5-1.cpp:64:11: warning: unused variable 'ref1' [-Wunused-variable]
  const A& ref1 = fn1(a); // fn1 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:66:11: warning: unused variable 'ref2' [-Wunused-variable]
  const A& ref2 = fn2(a); // fn2 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:68:11: warning: unused variable 'ptr1' [-Wunused-variable]
  const A* ptr1 = fn3(a); // fn3 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:70:11: warning: unused variable 'ref3' [-Wunused-variable]
  const A& ref3 = fn4(a); // fn4 called with T = A, an lvalue parameter from
           ^~~~
a7-5-1.cpp:73:11: warning: unused variable 'ref4' [-Wunused-variable]
  const A& ref4 = fn1(A{10}); // fn1 called with an rvalue parameter
           ^~~~
a7-5-1.cpp:78:11: warning: unused variable 'ptr2' [-Wunused-variable]
  const A* ptr2 = fn3(A{15}); // fn3 called with an rvalue parameter
           ^~~~
Rule A7-5-1 (required, implementation, automated)A function shall not return a reference or a pointer to a parameter that is passed by reference to const.(69)A7-5-1.cpp
$ g++-8 a7-5-1.cpp  -I./ -std=c++17  -Wall
a7-5-1.cpp: In function 'void f()':
a7-5-1.cpp:64:11: warning: unused variable 'ref1' [-Wunused-variable]
  const A& ref1 = fn1(a); // fn1 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:66:11: warning: unused variable 'ref2' [-Wunused-variable]
  const A& ref2 = fn2(a); // fn2 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:68:11: warning: unused variable 'ptr1' [-Wunused-variable]
  const A* ptr1 = fn3(a); // fn3 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:70:11: warning: unused variable 'ref3' [-Wunused-variable]
  const A& ref3 = fn4(a); // fn4 called with T = A, an lvalue parameter from
           ^~~~
a7-5-1.cpp:73:11: warning: unused variable 'ref4' [-Wunused-variable]
  const A& ref4 = fn1(A{10}); // fn1 called with an rvalue parameter
           ^~~~
a7-5-1.cpp:78:11: warning: unused variable 'ptr2' [-Wunused-variable]
  const A* ptr2 = fn3(A{15}); // fn3 called with an rvalue parameter
           ^~~~
Rule A7-5-1 (required, implementation, automated)A function shall not return a reference or a pointer to a parameter that is passed by reference to const.(69)A7-5-1.cpp
$ g++-8 a7-5-1.cpp  -I./ -std=c++2a  -Wall
a7-5-1.cpp: In function 'void f()':
a7-5-1.cpp:64:11: warning: unused variable 'ref1' [-Wunused-variable]
  const A& ref1 = fn1(a); // fn1 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:66:11: warning: unused variable 'ref2' [-Wunused-variable]
  const A& ref2 = fn2(a); // fn2 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:68:11: warning: unused variable 'ptr1' [-Wunused-variable]
  const A* ptr1 = fn3(a); // fn3 called with an lvalue parameter from an
           ^~~~
a7-5-1.cpp:70:11: warning: unused variable 'ref3' [-Wunused-variable]
  const A& ref3 = fn4(a); // fn4 called with T = A, an lvalue parameter from
           ^~~~
a7-5-1.cpp:73:11: warning: unused variable 'ref4' [-Wunused-variable]
  const A& ref4 = fn1(A{10}); // fn1 called with an rvalue parameter
           ^~~~
a7-5-1.cpp:78:11: warning: unused variable 'ptr2' [-Wunused-variable]
  const A* ptr2 = fn3(A{15}); // fn3 called with an rvalue parameter
           ^~~~
Rule A7-5-1 (required, implementation, automated)A function shall not return a reference or a pointer to a parameter that is passed by reference to const.(69)A7-5-1.cpp
```

#検討事項(agenda)
###1. 自律(freestanding)環境. 接待(hosted)環境

C++N4606 1.4 Implementation compliance p.4

###2. 対応OSの水準、対応通信規約、応用機能による分類
freestanding用の関数、ライブラリ等
###3. C++2014, C++2017, C++202aの比較項目
本件なし
###4. clang++, g++の比較検討項目
本件なし

###5 役立つまたは意味のある出力

#参考文献(reference)
###C++N4741 2018
Working Draft, Standard for Programming Language C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/n4741.pdf

C++N4741, 2018 Standard Working Draft on ISO/IEC 14882 sample code compile list
https://qiita.com/kaizen_nagoya/items/3294c014044550896010

###C++N4606 2016
Working Draft, Standard for Programming Language C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf

C++N4606, 2016符号断片編纂一覧(example code compile list)
 Working Draft 2016, ISO/IEC 14882(1)
https://qiita.com/kaizen_nagoya/items/df5d62c35bd6ed1c3d43/

#文書履歴(document history)
ver 0.10 初稿 20180611
ver 0.11 一覧追記 20180613