《STL源码剖析》chapter2空间配置器allocator

为什么不说allocator是内存配置器而说是空间配置器，因为空间不一定是内存，也可以是磁盘或其他辅助介质。是的，你可以写一个allocator，直接向硬盘取空间。sgi stl提供的配置器，配置的对象是内存。

 stl中allocator用法参考以前的http://www.cnblogs.com/youxin/archive/2012/06/07/2540170.html。

书中jj allocator类

#ifndef _JJALLOC
#define _JJALLOC
#include<new> //for placement new
#include<cstddef> //for ptrdiff_t ,size_t
#include<cstdlib> //for exit()
#include<climits> //for UINX_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,invoke constuctor of t1
}

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;

    //rebind allocator of type U
    template<class U>
    struct rebind{
        typedef allocator<U> other;
    };
    //需要加上以下2个函数，windows的编译器用到了allocator不同类型的拷贝， 
     allocator()  
        {  
            return ;  
        }  
              
        template <class U>  
        allocator(const allocator<U>& c )  
        {  
        }  

    //hint user for locality,第2个参数是个提示，实现上可能会利用它来增进区域性（locality），或完全忽略之
    
    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));
    }
};
}//#end of namespace JJ
#endif

#include"2jjalloc.h"
#include<vector>
#include<iostream>
using namespace std;

int main()
{
    int ia[5]={0,1,2,3,4};
    unsigned int i;
    
    vector<int,JJ::allocator<int> > iv(ia,ia+5);
    for(i=0;i<iv.size();i++)
        cout<<iv[i]<<ends;
    cout<<endl;
}

这个allocator只能有限程序带票PJ STL，