STL_2_空间分配器_2

本文章内容来源于《STL源码分析》第二章

---

2 内存基本处理工具

• STL有五个全局函数：作用于未初始化空间

  • construct()
  • destroy()
  • uninitialized_copy() ==>对应高层函数copy()
  • uninitialized_fill() ==> fill()
  • uninitialized_fill_n() ==> fill_n()

• 后面三个低层次函数：

• 定义于<memory>

• SGI 定义于：<stl_uninitialized>

• POD： plain Old Data : 标量型别或者传统的 c struct 型别：如char, int等等；

• POD: 此型别必然有用trivial ctor/dtor/ copy/ assignment函数。可以采用类似memcpy之类的高效率函数；

• Non-POD: 采用最保险的做法；

• __type_triats: 萃取型别的特性；

  • 如typedef __type_traits<T>::is_POD_type is_POD 判断T是否POD模型；
  • traits具体查看《STL源码分析》第三章;

2.1 uninitialized_copy

• 主要接口

  // uninitialized_copy
  template<class InputIterator, class ForwardIterator>
  ForwardIterator uninitialized_copy(InputIterator first, InputIterator last,
    ForwardIterator result){
        retun __uninitialized_copy(first,last, result, value_type(result));
        // 利用value_type() 取出first de value_type
    }
  

• POD判别函数

  // POD  判断
  template<class InputIterator, class ForwardIterator, class T>
  inline ForwardIterator
  __uninitialized_copy(InputIterator first, InputIterator last, 
        ForwardIterator result ,T*){
            typedef typename __type_traits<T>::is_POD_type is_POD;
            return __uninitialized_copy_aux(first, last, result, is_POD());
  }
  

• POD型别

template<class InputIterator, class ForwardIterator, class T>
inline ForwardIterator
__uninitialized_copy_aux(InputIterator first, InputIterator last,
        ForwardIterator result, __true_type){
            return copy(first, last, result);   // 调用STL算法 copy()
        }    

• non-POD型别

template<class InputIterator, class ForwardIterator, class T>
inline ForwardIterator
__uninitialized_copy_aux(InputIterator first, InputIterator last,
        ForwardIterator result, __false_type){
            ForwardIterator cur = result;
            // 异常处理省略
            for(;first != last; ++first, ++cur){
                construct(&*cur, *first);   // 必须一个一个元素构造
            }
            return cur;

        }    

• 针对char*, wchar_t*的版本

inline char* uninitialized_copy(const char* first, const char* last, char* result){
    memmove(result, first, last - first);
    return result + (last - first);
} 

inline wchar_t* uninitialized_copy(const wchar_t* first, const wchar_t* last,
    wchar_t* result){
    memmove(result, first, sizeof(wchar_t)*(last - first));
    return result+(last - first);
}

2.2 uninitialized_fill

• 在i出调用construct(&*i, x)

template<class ForwardIterator, class T>
void uninitialized_fill(ForwardIterator first, ForwardIterator last, const T& x){
    __uninitialized_fill(first, last, x, value_type(first));
}

• 判断POD

template<class ForwardIterator , class T, class T1>
inline void __uninitialized_fill(ForwardIterator first, ForwardIterator last,
    const T& x, T1*){
        typedef typename __type_traits<T>::is_POD_type is_POD;
        __uninitialized_fill_aux(first, last, x, is_POD());
    }

• POD型别

template<class ForwardIterator , class T, class T1>
inline void __uninitialized_fill(ForwardIterator first, ForwardIterator last,
    const T& x, __true_type){
        fill(first, last, x);  // 调用STL算法 fill()

}

• non-POD型别

template<class ForwardIterator , class T, class T1>
inline void __uninitialized_fill(ForwardIterator first, ForwardIterator last,
    const T& x, __false_type){
                    ForwardIterator cur = result;
            // 异常处理省略
            for(;first != last; ++first, ++cur){
                construct(&*cur, *first);   // 必须一个一个元素构造
            }
            return cur;

}

2.3 uninitialized_fill_n

1. 首先使用萃取器取出first的value type,
2. 然后判断型别是否为POD型别（plain old data）,即标量型别，或者传统的 c struct型别；
3. pod必然有用无用的trivial ctor/copy/dtor/assignment函数
4. 对pod采用memcpy之类高效率的函数,non-pod采用保险的做法；

• 接口

template<class ForwardIterator , class Size, class T>
inline ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n, const T& x){
    return __uninitialized_fill_n(first,n, x, value_type(first));
}

• POD型别判断

template <class ForwardIterator , class Size, class T,class T1>
inline ForwardIterator __uninitialized_fill_n(ForwardIterator first,
    Size n , const T& x, T1*){
        typedef typename __type_traits<T1>::is_POD_type is_POD;
        return __uninitialized_fill_n_aux(first, n, x, is_POD());
    }

• POD 型别

template <class ForwardIterator , class Size, class T>
inline ForwardIterator __uninitialized_fill_n_aux(ForwardIterator first,
    Size n , const T& x, __true_type){
        return fill_n(first, n, x);  // 告诫函数执行
    }

• non-POD型别

template<class ForwardIterator, class Size, class T>
inline ForwardIterator __uninitialized_fill_n_aux(ForwardIterator first,
    Size n, const T& x, __false_type){
        ForwardIterator cur = first;
        for(; n>0; --n, ++cur){
            construct(&*cur, x);
        }
        return cur;
    }

---