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Effective C++ Third version, sample code compile list(18) Make interfaces easy to use correctly and hrad to use incorrectly

Last updated at 2024-06-03Posted at 2019-05-05

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

<この項は書きかけです。順次追記します。>

算譜(source code)

ec18.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>
using namespace std;

const char * msg ="Item 18: Make interfaces easy to use correctly and hrad to use incorrectly";


/// From here "Effective C++


class Date {
public:
    Date(int month, int day, int year);
};

// May be misused
Date d(30, 3, 1995);

// can be prevented by introdution of new types
struct Day {
    explicit Day(int d) : val(d) {}
    int val;
};
///...
class Date {
public:
    Date(const Month& m, const Day& d, const Year& y);
};
Date(Month(3), Day(30), Year(1995));
//Restrict the values

class Month {
public:
    static Month Jan() { return Month(1); }
    static Month Feb() { return Month(2); }
  ///  ...
private:
    explicit Month(int m);
};
Date d(Month::Mar(), Day(30), Year(1995));
//Have your types behave consistently with the built-in types.

if (a*b = c)
//size() function in STL containers.

//To avoid resource leak:

Investment* createInvestment();

std::tr1::shard_ptr<Investment> createInvestment();  // force clients to store the return value in a tr1::shared_ptr
declare deleter in shared_ptr

// create a null shared_ptr with getRidOfInvestment as its deleter
std::tr1::shared_ptr<Investment> pInv(static_cast<Investment*>(0), getRidOfInvestment); 
//Cross-DLL problem: an object is created using new in one dynamically linked library but is deleted in a different DLL.

//shared_ptr prevents this problem.

//Things to Remember

//Good interfaces are easy to use correctly and hard to use incorrectly. You should strive for these characteristics in all your interfaces.
//Ways to facilitate correct use include consistency in interfaces and behavioral compatibility with built-in type.
//Ways to prevent errors include creating new types, restricting operations on types, constraining object values, and eliminating client resource management reponsiblities.
//tr1::shared_ptr supports custom deleters. This prevents the cross-DLL problem, can be used to automatically unlock mutexes (see Item 14), etc.

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

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

編纂・実行結果(compile and go)

cpa.sh

$ ../cpa.sh ec16
$ clang++ ec16.cpp -I./ -std=c++14 -Wall
Item 16: Use the same form in corresponding uses of new and delete
$ clang++ ec16.cpp  -I./ -std=c++17 -Wall
Item 16: Use the same form in corresponding uses of new and delete
$ clang++ ec16.cpp  -I./ -std=c++2a -Wall
Item 16: Use the same form in corresponding uses of new and delete

$ g++-8 ec16.cpp  -I./ -std=c++14  -Wall
Item 16: Use the same form in corresponding uses of new and delete
$ g++-8 ec16.cpp  -I./ -std=c++17  -Wall
Item 16: Use the same form in corresponding uses of new and delete
$ g++-8 ec16.cpp  -I./ -std=c++2a  -Wall
Item 16: Use the same form in corresponding uses of new and delete