文章标题

来源：互联网发布：免费的音乐软件编辑：程序博客网时间：2024/05/24 03:19

STL源码分析2.1

2.1.1设计一个简单的空间配置器

#ifndef SIMPLESTL_H_#define  SIMPLESTL_H_#include <new>#include <cstddef>#include <cstdlib>#include <climits>#include <iostream>namespace JJ{    template<typename T>    inline T* _allocate(ptrdiff_t size, T*)    {        //函数原型为set_new_handler(x)        //x是一个函数指针,当new不成功时回调x函数.当x为0时,表示回调函数为空的        //这个时候若new失败,默认的内存分配函数会直接抛出bad_alloc异常        std::set_new_handler(0);        //operator new函数,只分配所要求的空间,而并不调用相关对象的构造函数        //当无法满足所要求分配的空间时,会调用new_handler,若new_handler为空指针        //直接抛出bad_alloc异常        T* temp = (T*)(::operator new((size_t)(size * sizeof(T))));        if (temp == 0)        {            cerr << "out of memory" << endl;            exit(1);        }        return temp;    }    template<typename T>    inline void _deallocate(T* buffer)    {        ::operator delete(buffer);    }    template<typename T1,typename T2>    inline void _construct(T1* p, const T2& value)    {        //placement new        //p为指向一块已分配内存的指针.T1为构造对象的类型        //value??        new(p)T1(value);    }    template<typename T>    inline void _destroy(T* ptr)    {        ptr->~T();    }    template<typename T>    class Allocator    {    public:        typedef T               value_type;        typedef T*              pointer;        typedef const T*        const_pointer;        typedef T&              reference;        typedef const T&        constreference;        typedef size_t          size_type;        typedef ptrdiff_t       difference_type;        //rebind allocator of type U        template<typename U>        struct rebind        {            typedef Allocator<U> other;        };        //hint used for locality        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(reference x){ return (const_pointer)&x; }        size_type max_size() const        {            return size_type(UINT_MAX / sizeof(T));        }    };}#endif

cpp文件如下:

#include "simpleSTL.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] << ' ';        cout << endl;    }    return 0;}

再在namespace JJ中增加类增加新类Testint

class Testint    {    private:        int a;    public:        Testint(int b) :a(b){}        ~Testint()        {            std::cout << "Destructor called" << std::endl;        }        friend std::ostream& operator<<(std::ostream& os,const Testint& testint);    };    std::ostream& operator<<(std::ostream& os,const Testint& testint)    {        os << testint.a;        return os;    }

修改下main函数后可以看到适配器也可以正常运行

0 0