STL 内存管理 简单说说STL的内存管理
人气:41. 概述
STL Allocator是STL的内存管理器，也是最低调的部分之一，你可能使用了3年stl，但却不知其为何物。
STL标准如下介绍Allocator
the STL includes some low-level mechanisms for allocating and deallocating memory. Allocators are very specialized, and you can safely ignore them for almost all purposes. Allocators encapsulate allocation and deallocation of memory. They provide a low-level interface that permits efficient allocation of many small objects; different allocator types represent different schemes for memory management.
<STL 源码剖析>将其描述为空间配置器，理由是allocator可以将其它存储介质（例如硬盘）做为stl 容器的存储空间。由于内存是allocator管理的主要部分，因此，本文以STL内存管理为出发点介绍allocator。
Allocator就在我们身边，通常使用STL的方式：
#include <vector>
std::vector<int> Array(100);
本质上，调用的是：
#include <vector>
std::vector<int, std::allocator> Array(100);
std::allocator就是一个简单的Allocator
2. 使用
针对不同的应用场合，STL中实现了不同的Allocator，如下（gcc-3.4：http://www.cs.huji.ac.il/~etsman/Docs/gcc-3.4-base/libstdc++/html/20_util/allocator.html）:
__gnu_cxx::new_allocator<T> Simply wraps ::operator new and ::operator delete.
__gnu_cxx::malloc_allocator<T> Simply wraps malloc and free. There is also a hook for an out-of-memory handler
__gnu_cxx::debug_allocator<T> A wrapper around an arbitrary allocator A. It passes on slightly increased size requests to A, and uses the extra memory to store size information.
__gnu_cxx::__pool_alloc<bool, int> A high-performance, single pool allocator. The reusable memory is shared among identical instantiations of this type.
__gnu_cxx::__mt_alloc<T> A high-performance fixed-size allocatorthat was initially developed specifically to suit the needs of multi threaded applications
__gnu_cxx::bitmap_allocato A high-performance allocator that uses a bit-map to keep track of the used and unused memory locations
例如，在多线程环境下，可以使用：
#include <vector>
#include <mt_allocator.h>
std::vector<int, __gnu_cxx::__mt_alloc<int>> Array(100);
3.一个简单的Allocator实现
我们可以实现自己的allocator
#include <memory>
template<class T>
class my_allocator : public std::allocator<T>
{
public:
typedef std::allocator<T> base_type;
// 必须要重新定义
template<class Other>
struct rebind
{
typedef my_allocator<Other> other;
};
// 内存的分配与释放可以实现为自定义的算法
pointer allocate(size_type count)
{
return (base_type::allocate(count));
}
void deallocate(pointer ptr, size_type count)
{
base_type::deallocate(ptr, count);
}
// 构造函数
my_allocator()
{}
my_allocator(my_allocator<T> const&)
{}
my_allocator<T>& operator=(my_allocator<T> const&)
{
return (*this);
}
template<class Other>
my_allocator(my_allocator<Other> const&)
{}
template<class Other>
my_allocator<T>& operator=(my_allocator<Other> const&)
{
return (*this); }
};
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