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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

Effective C++ Third version, sample code compile list(13)Use objects to manage resources

Posted at

Effective C++: 55 Specific Ways to Improve Your Programs and DesignsThird version by Scott Mayers
https://www.informit.com/store/effective-c-plus-plus-55-specific-ways-to-improve-your-9780321334879
https://www.amazon.com/dp/0321334876

Sample code from
Yuzhen11/Effective_CPP
https://github.com/Yuzhen11/Effective_CPP

#算譜(source code)

ec13.cpp
///Effective C++:  55 Specific Ways to Improve Your Programs and DesignsThird version by Scott Mayers
///https://www.informit.com/store/effective-c-plus-plus-55-specific-ways-to-improve-your-9780321334879
#include <iostream>
#include <cstdlib>
#include <vector>
using namespace std;

const char * msg ="Item 13: Use objects to manage resources";

/// From here "Effective C++

///namespace A{

class Investment {
};
Investment * createInvestment() {};

void f() {
  Investment* pInv = createInvestment();  // call factory function
///    ...   // something bad may happen
  delete pInv;  // release object
}
//Put that resource inside an object whose destructor will automatically release the resource when control leaves f.
///}

namespace B {
  void f() {
    std::auto_ptr<Investment> pInv(createInvestment());  // call factory function
  }
//auto_ptrs have an unusual characteristic: copying them sets them null.
}

void g1() {
  std::auto_ptr<Investment> pInv1(createInvestment);
  std::auto_ptr<Investment> pInv2(pInv1);  // pInv2 now points to the object; pInv1 is now null

  pInv1 = pInv2;  // now pInv1 points to the object, and pInv2 is null
//shared_ptr behaves well.
}

void g2() {
  std::tr1::shared_ptr<Investment> pInv1(createInvestment);
  std::tr1::shared_ptr<Investment> pInv2(pInv1);  // both pInv1 and pInv2 now point to the object

  pInv1 = pInv2;  // ditto
}

//Two critical aspects of using objects to managing resources:

//Resources are acquired and immediately turned over to resource-managing objects.
//Resource-managing objects use their destructors to ensure that resources are released.

//Things to Remember

//To prevent resource leaks, use RAII objects that acquire resource in their constructors and release them in their destructors.
//Two commonly useful RAII classes are tr1::shared_ptr and auto_ptr. tr1::shared_ptr is usually the better choice, because its behavior when copied is intuitive. copying an auto_ptr sets it to null.

/// to here from "Effective C++"

int main() {
  cout << msg << endl;
  return EXIT_SUCCESS;
}

#編纂・実行結果(compile and go)

cpa.sh
$ ../c1.sh ec13
$ clang++ ec13.cpp  -std=c++2a -Wall
ec13.cpp:16:33: warning: control reaches end of non-void function [-Wreturn-type]
Investment * createInvestment(){};
                                ^
ec13.cpp:28:10: error: no member named 'auto_ptr' in namespace 'std'
    std::auto_ptr<Investment> pInv(createInvestment());  // call factory function
    ~~~~~^
ec13.cpp:28:19: error: 'Investment' does not refer to a value
    std::auto_ptr<Investment> pInv(createInvestment());  // call factory function
                  ^
ec13.cpp:14:7: note: declared here
class Investment {
      ^
ec13.cpp:28:31: error: use of undeclared identifier 'pInv'
    std::auto_ptr<Investment> pInv(createInvestment());  // call factory function
                              ^
ec13.cpp:34:6: error: no member named 'auto_ptr' in namespace 'std'
std::auto_ptr<Investment> pInv1(createInvestment);
~~~~~^
ec13.cpp:34:15: error: 'Investment' does not refer to a value
std::auto_ptr<Investment> pInv1(createInvestment);
              ^
ec13.cpp:14:7: note: declared here
class Investment {
      ^
ec13.cpp:34:27: error: use of undeclared identifier 'pInv1'
std::auto_ptr<Investment> pInv1(createInvestment);
                          ^
ec13.cpp:35:6: error: no member named 'auto_ptr' in namespace 'std'
std::auto_ptr<Investment> pInv2(pInv1);  // pInv2 now points to the object; pInv1 is now null
~~~~~^
ec13.cpp:35:15: error: 'Investment' does not refer to a value
std::auto_ptr<Investment> pInv2(pInv1);  // pInv2 now points to the object; pInv1 is now null
              ^
ec13.cpp:14:7: note: declared here
class Investment {
      ^
ec13.cpp:35:33: error: use of undeclared identifier 'pInv1'
std::auto_ptr<Investment> pInv2(pInv1);  // pInv2 now points to the object; pInv1 is now null
                                ^
ec13.cpp:37:1: error: use of undeclared identifier 'pInv1'
pInv1 = pInv2;  // now pInv1 points to the object, and pInv2 is null
^
ec13.cpp:37:9: error: use of undeclared identifier 'pInv2'
pInv1 = pInv2;  // now pInv1 points to the object, and pInv2 is null
        ^
ec13.cpp:42:6: error: no member named 'tr1' in namespace 'std'
std::tr1::shared_ptr<Investment> pInv1(createInvestment);
~~~~~^
ec13.cpp:43:6: error: no member named 'tr1' in namespace 'std'
std::tr1::shared_ptr<Investment> pInv2(pInv1);  // both pInv1 and pInv2 now point to the object
~~~~~^
1 warning and 13 errors generated.

#課題(agenda)
1)役に立つまたは意味のあるコンパイルエラーを取る方法

2)役に立つまたは意味のある関数、クラスの呼び出し方

3)役に立つまたは意味のある出力

#参考資料(reference)

docker gnu(gcc/g++) and llvm(clang/clang++)
https://qiita.com/drafts/059874ea39c4de64c0f7
[C][C++]の国際規格案の例題をコンパイルするときの課題７つ。
https://qiita.com/kaizen_nagoya/items/5f4b155030259497c4de
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
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
C++参考資料一覧
https://researchmap.jp/joub9b3my-1797580/#_1797580

#文書履歴(document history)

ver. 0.10 初稿 20180622

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