简单空间配置器

一个简单的空间配置器, JJ::allocator:

<span style="font-family:Courier New;font-size:14px;">#ifndef __JJALLOC_
#define __JJALLOC_

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


namespace JJ {

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

template <class T1, class T2>
inline void _construct(T1* p, const T2& value) {
	new(p) T1(value);	//placement new. 将p作为地址传入operate new函数
				//不进行分配操作, 调用T1::T1(value)
}

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

template <class 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;

	template <class U>
	struct rebind {
		typedef allocator<U> other; 
		//以list为例, allocator<int>::rebind<node>::other即为allocator<node>
	};

	//第二个参数是个提示, 实现上可能会利用它来增进区域性(locality), 或者完全忽略之
	pointer allocate(size_type 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, const 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));
	}
};

}


#endif</span>

SGI标准空间配置器, std::allocator源码:

<span style="font-family:Courier New;font-size:14px;">#ifndef DEFALLOC_H
#define DEFALLOC_H

#include <new.h>
#include <stddef.h>
#include <stdlib.h>
#include <limits.h>
#include <iostream.h>
#include <algobase.h>


template <class T>
inline T* allocate(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 <class T>
inline void deallocate(T* buffer) {
    ::operator delete(buffer);
}

template <class 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;
    pointer allocate(size_type n) { 
	return ::allocate((difference_type)n, (pointer)0);
    }
    void deallocate(pointer p) { ::deallocate(p); }
    pointer address(reference x) { return (pointer)&x; }
    const_pointer const_address(const_reference x) { 
	return (const_pointer)&x; 
    }
    size_type init_page_size() { 
	return max(size_type(1), size_type(4096/sizeof(T))); 
    }
    size_type max_size() const { 
	return max(size_type(1), size_type(UINT_MAX/sizeof(T))); 
    }
};

//模板特化需要加template<>, 此处为gcc特性
class allocator<void> {   
public:
    typedef void* pointer;
};



#endif
</span>