allocator是c++标准库中用于管理内存的一个类。主要包括以下类方法:
代码如下(来源于《STL源码剖析》):
#ifndef _JJALLOC_
#define _JJALLOC_
#include <new> //for placement new
#include <cstddef>
#include <cstdlib>
#include <climits>
#include <iostream>
namespace JJ
{
template <class T>
inline T* _allocate(ptrdiff_t size, T*) //分配size * sizeof(T)的内存
{
set_new_handler(0);
T* tmp = (T*)(::operator new((size_t)(size * sizeof(T)))); //申请内存
if (tmp == 0)
{
cerr << "out of memory" << endl;
}
return tmp;
}
template <class T>
inline void _deallocate(T* buffer)
{
::operator delete(buffer); //为什么不用 delete [] ? ,operator delete 区别于 delete
//是一个操作符
}
template <class T1,class T2>
inline void _construct(T1 *p, const T2 &value)
{
new(p) T1(value); //用value 函数初始化 *p ?
//placement new的用法,p内存地址已存在
}
template <class T>
inline void _destory(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;
};
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 destory(pointer p) { _destory(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)); //最多分配T元素数
}
};
}
参考:《STL源码剖析》P45-46
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