C ++单例与私有构造函数 [英] C++ singleton with private constructor

问题描述

我需要单一的应用程序生命周期，保证创建/销毁和静态访问它。

  #include< iostream> ; 
 #include< cstdlib> 
 
 #define DISALLOW_COPY_AND_ASSIGN（TypeName）\ 
 TypeName（const TypeName&）; \ 
 void operator =（const TypeName&）
 
 #define M（）C :: sM（）
 #define M2（）C :: sM2 
 $ b using namespace std; 
 
 class C {
 private：
 static C * s; 
 
〜C（）{cout< 〜C（）< endl; } 
 static C * instance（）{
 if（s == NULL）{s = new C（）; } 
 cout<< instance（）=< s<< endl;返回s; 
} 
 static void cleanUp（）{delete s; } 
 void m（）{cout<< m（）< endl; } 
 void m2（）{cout<< m2（）< endl; } 
 DISALLOW_COPY_AND_ASSIGN（C）; 
 public：
 C（）{
 cout<< C（）< endl; if（s == NULL）{
 s = this; atexit（& cleanUp）; 
 cout<< cleanUp is installed< endl; 
} else {
 cout<< cleanUp未安装< endl; 
} 
} 
 void * operator new（size_t sz）{
 void * p = NULL; if（s == NULL）{p = new char [sz]; } else {p = s; } 
 cout<< new（<< sz<<）=< p < endl; 
 return p; 
} 
 void operator delete（void * p，size_t sz）{
 cout< delete（<< sz<<，<< p<<）< endl; 
 if（p）delete [] static_cast< char *>（p）; s = NULL; 
} 
 void static sM（）{cout<< sM（）< endl; instance（） - > m（）; } 
 void static sM2（）{cout< sM2（）< endl; instance（） - > m2（）; } 
}; 
 
 C * C :: s = NULL; 
 
 int main（）{
 M（）; 
 M2（）; 
 C * p1 = new C（）; 
 C * p2 = new C（）; 
} 
  

但我不知道如何摆脱g ++警告： p>

  test.cpp：在静态成员函数'static void C :: operator delete（void *，size_t）'：
 test.cpp：22：warning：删除'void *'未定义
  

of void *，析构函数开始在无限循环中调用自身。任何人都可以帮助我获得干净的代码，没有警告？

要删除的类型是 char * c>：

  void operator delete（void * p，size_t sz）{
 cout< delete（<< sz<<，<< p<<）< endl; 
 if（p）delete（char *）p; 
} 
  

您的新版本中有一个错误：新的char [10]和新的char（10）之间的区别

也许应该是：

  p = new char [sz]; 
  

，然后

 code> delete []（char *）p; 
  

----编辑：

纯粹主义的删除，牺牲人们学习的清晰度; P：

  delete [] static_cast< char *>（p）; 
  

（*我真的很感激关于演员表的注意事项）

I need singleton with a application lifetime, guaranteed creation/destruction and static access to it.

#include <iostream>
#include <cstdlib>

#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
    TypeName(const TypeName&);             \
    void operator=(const TypeName&)

#define M() C::sM()
#define M2() C::sM2()

using namespace std;

class C {
  private:
    static C* s;

    ~C() { cout << "~C()" << endl; }
    static C* instance() { 
        if (s==NULL) { s=new C(); }
        cout << "instance()=" << s << endl; return s; 
    }
    static void cleanUp() { delete s; }
    void m() { cout << "m()" << endl; }
    void m2() { cout << "m2()" << endl; }
    DISALLOW_COPY_AND_ASSIGN(C);
  public:
    C() { 
        cout << "C()" << endl; if (s==NULL) { 
            s=this; atexit(&cleanUp); 
            cout << "cleanUp is installed" << endl; 
        } else { 
            cout << "cleanUp is not installed" << endl; 
        } 
    }
    void* operator new(size_t sz) { 
        void* p=NULL; if (s==NULL) { p=new char[sz]; } else { p=s; }
        cout << "new(" << sz << ")=" << p << endl;
        return p;
    }
    void operator delete(void* p, size_t sz) { 
        cout << "delete(" << sz << "," << p << ")" << endl;
        if (p) delete[] static_cast<char*>(p); s=NULL; 
    }
    void static sM() { cout << "sM()" << endl; instance()->m(); }
    void static sM2() { cout << "sM2()" << endl; instance()->m2(); }
};

C* C::s = NULL;

int main() {
    M();
    M2();
    C* p1 = new C();
    C* p2 = new C();
}  

But I don't know how to get rid of g++ warning:

test.cpp: In static member function 'static void C::operator delete(void*, size_t)':
test.cpp:22: warning: deleting 'void*' is undefined

If I write C* instead of void*, destructor start calling itself in infinite loop. Can anybody help me to get clean code without warnings? C++98 of course.

解决方案

The type to delete is char*:

void operator delete(void* p, size_t sz) { 
    cout << "delete(" << sz << "," << p << ")" << endl;
    if (p) delete (char*) p;
}

There is a bug in your new: What's the difference between new char[10] and new char(10)

Maybe should be:

p=new char[sz];

and then

delete[] (char*)p ;

---- edited:

The delete for purists, sacrificing clarity to people learning ;P :

delete[] static_cast<char*>(p) ;

(*actually I appreciate the note about the cast)

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