一个简单的空间配置器: allocator

这个简单实现类中的方法主要是有

allocate()
deallocate()
construct()
destroy()

实际在SGI STL中construct()和destroy()是以全局函数的方式出现的~~

//jjalloc.h
#ifndef JJALLOC_H
#define JJALLOC_H

#include <new>		//for placement new
#include <cstddef>	//for ptrdiff_t, size_t
#include <cstdlib>	//for exit(1)
#include <iostream>	//for cerr
#include <climits>	//for UINT_MAX

namespace JJ {

template <typename T>
inline T* _allocator(ptrdiff_t size, T*) {
	set_new_handler(0);
	T *tmp = (T*)(::operator new((size_t)(size * sizeof(T))));
	if(tmp == 0) {
		cerr << "out of memory" << endl;
		exit(1);
	}
	return tmp;
}

template <typename T>
inline void _deallocate(T *buffer) {
	::operator delete(buffer);
}

template <typename T1, typename T2>
inline void _construct(T1 *p, const T2 &value) {
	new(p) T1(value);                                          //定位new表达式
}

template <typename T>
inline void _destroy(T *ptr) {
	ptr->~T();
}

template <typename T>
class allocator {
public:
	typedef T value_type;
	typedef T* pointer;
	typedef const T* const_pointer;
	typedef T& reference;
	typedef const T& const_reference;
	typedef size_t size_type;
	typedef ptrdiff_t difference_type;

	//rebind allocator of type U
	template <typename U>
	struct rebind {
		typedef allocator<U> other;
	};

	//hint used for locality
	pointer allocate(size_t n, const void *hint=0) {
		return _allocate((difference_type)n, (pointer)0);
	}

	void deallocate(pointer p, size_type n) {
		_deallocate(p);
	}

	void construct(pointer p, T &value) {
		_construct(p, value);
	}

	void destroy(pointer p) {
		_destroy(p);
	}

	pointer address(reference x) {
		return (pointer)&x;
	}

	const_pointer const_address(const_reference x) {
		return (const_pointer)&x;
	}

	size_type max_size() const {
		return size_type(UINT_MAX/sizeof(T));
	}
};

}	//end of namespace

#endif