New Handler

1.new handler

   （1）当operator new 没能力为你分配出你所申请的memory，会抛一个std::bad_alloc exception。某些老编译器则是返回0---你仍然可以令编译器那么做：

             new (nothrow) Foo;

             此为nothrow形式。

   （2）抛出exception之前会先（不止一次）调用一个可由client指定的handler，以下是new handler的形式和设定方法：

             typedef void (*new_handler)();

             new_handlerset_new_handler(new_handler p) throw();

   （3）设计良好的new handler只有两种选择：

            [1]更多memory可用

            [2]调用abort()或exit()、

   （4）

            void* operator new(size_t size, const std::nothrow_t&)

                                                _THROW0()

            {
                   //try to allocate size bytes
                   void* p;
                   while((p = malloc(size)) == 0) {
                           //buy more memory or return null pointer
                  _TRY_BEGIN
                           if( _callnewh(size) == 0) break;
                  _CATCH(std::bad_alloc) return (0);
                  _CATCH_END
                  }
                  return (p);

          }

 （5）示例

   

#include 
#include 
#include 

using namespace std;


void noMoreMemory() {
	cout << "Out of memory";
	abort();
}


int main() {
	set_new_handler(noMoreMemory);
	
	int* p = new int[100000000000000000];
	assert(p);

	p = new int[10000000000000];
	assert(p);
	
	return 0;
}

本例中的new handler中若无调用abort()，执行后cerr会不断出现"out of memory"，需强制中断。这样的表现是正确的，表示当operator new无法满足申请量时，会不断调用new handler直到获得足够memory

（6）new_handler __cdecl set_new_handler(

                                            new_handlernew_p)

           {

                     //cannot use stub to register a new handler

                    assert(new_p == 0);

                    //remove current handler

                    _set_new_handler(0);

                    return 0;

           }

2.=default，=delete

  class Foo {

  public:

            Foo() = default;

            Foo(const Foo&) = default;

            Foo& operator=(const Foo&) = delete;

            ~Foo() = default;

  };

  it is not only for constructors and assignments,but also applies to operator new/new[],operator delete/delete[] and their overloads.

#include 
using namespace std;


class Foo {
public:
	long L;
public:
	Foo() {
	}
	Foo(long l): L(l) {
	}
	//static void* operator new(size_t size) = default;
	//error: 'static void* Foo::operator new(size_t)' cannot be defaulted
	//static void operator delete(void* pdead, size_t size) = default;
	//error: 'static void Foo::operator delete(void*, size_t)' cannot be defaulted
	static void* operator new[](size_t size);
	static void operator delete[](void* pdead, size_t size);
};


class Goo {
public:
	long L;
public:
	Goo() {
	}
	Goo(long l): L(l) {
	}
	
	static void* operator new(size_t size) = delete ;
	static void operator delete(void* pdead, size_t size) = delete ;
};



int main() {
	Foo* p1 = new Foo(5);
	delete p1;
	
	//Foo* pF = new Foo[10];
	//delete[] pF;
	
	//Goo* p2 = new Goo(7);
	//delete p2;
	
	Goo* pG = new Goo[10];
	delete[] pG;
	
	return 0;
}