nanxing_stl/lib/basic/nanxing_defalloc.h

#ifndef _DEF_ALLOC_
#define _DEF_ALLOC_ 1
#include<iostream>
#include<cstddef>
#include<new>
#include<climits>
namespace nanxing
{
	template<typename T>
	constexpr
	inline T* _allocate(ptrdiff_t size, T*) noexcept                  //这个是STL标准的要求，第二个传入的T*没啥用（在实际调用的时候会传入一个空指针）
	{
		T* temp;
		try
		{
			temp = (T*)(::operator new((size_t)(size * (sizeof(T)))));
		}
		catch(...)
		{
			return nullptr;                                        //如果出现失败会直接返回nullptr
		}
		return temp;
	}


	//template<typename T1,typename T2>
	// inline void _construct(T1* p, const T2& x)
	// {
	// 	::new(p) T1(x);   //在p指向空间上调用构造函数
	// }

	template<typename _Up, typename... _Args>
	inline void _construct(_Up* __p, _Args&&... __args) noexcept(std::is_nothrow_constructible<_Up, _Args...>::value)
	{ 
		::new((void *)__p) _Up(std::forward<_Args>(__args)...); 
	}	
	

	template<typename T>
	constexpr
	inline void _deallocate(T* buffer)
	{
		::operator delete(buffer);                   //释放空间（注意和delete的区别）
	}

	template<typename T>
	constexpr
	inline void _destory(T* ptr)
	{
		ptr->~T();                     //调用析构函数
	}

	template<typename T>
	class allocator
	{
	public:
		using value_type = T;
		using pointer = T*;
		using const_pointer = const T*;
		using reference = T&;
		using size_type = size_t;
		using difference_type = ptrdiff_t;
		using const_reference = const T&;
		
		constexpr  allocator() noexcept
		{
			//std::cout<<"hello"<<std::endl;
		}
		template<typename U> struct rebind
		{
			using other = allocator<U>;
		};
		constexpr pointer allocate(size_type n, const void* hint = 0)           //注意这个函数是会抛出一个std::bad_alloc异常
		{
			return _allocate((difference_type)n, (pointer)0);
		}

		
		template<typename... _Args>
		void construct(pointer __p, _Args&&... __args) noexcept
		{ 
			_construct(__p,std::forward<_Args>(__args)...);
			//::new((void *)__p) _Up(std::forward<_Args>(__args)...); 
		}	

		// template<pointer,typename T2>
		// void construct(pointer p,const T2& data )noexcept         //唯一参数版本
		// {
		// 	_construct(p,data);
		// }
		constexpr void deallocate(pointer p, size_type n=0)
		{
			_deallocate(p);
		}

		constexpr void destory(pointer p)
		{
			_destory(p);
		}

		constexpr pointer address(reference x)
		{
			return (pointer)&x;
		}
		constexpr const_pointer address(const_reference x)
		{
			return (const_pointer)&x;
		}
		
		constexpr size_type max_size()const
		{
			return size_type(UINT_MAX / sizeof(T));
		}
	};
}

#endif