求助 stl 里的__type_traits

[noein115]

template<>
struct __type_traits<int>{
	typedef __true_type has_trivial_default_constructor;
	typedef __true_type has_trivial_copy_constructor;
	typedef __true_type has_trivial_assignment_operator;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};

我照着stl 写了这样的 int long double 等等 很多段

然后写一个函数

template <class ForwardIterator,class T>
inline void destroy(ForwardIterator first,ForwardIterator last){
typedef typename __type_traits<T>::

到这里时 ::后 没出现任何选项

状态栏里显示 " .或 -> 左边的表达式具有无法解析的类型"


怎么会无效?

[ryfdizuo]

你编译有错吗？
type trait只是萃取类型。。。

[noein115]

没编译...

destroy函数是在另外一个 construct.h 头文件里写的..

[we_sky2008]

#include <iostream> 

using namespace std; 

struct __true_type
{

};

struct __false_type
{

};

template<class T>
struct __type_traits
{
    typedef __false_type has_trivial_default_constructor;
    typedef __false_type has_trivial_copy_constructor;
    typedef __false_type has_trivial_assignment_operator;
    typedef __false_type has_trivial_destructor;
    typedef __false_type is_POD_type;
};

template<>
struct __type_traits<int>
{
    typedef __true_type has_trivial_default_constructor;
    typedef __true_type has_trivial_copy_constructor;
    typedef __true_type has_trivial_assignment_operator;
    typedef __true_type has_trivial_destructor;
    typedef __true_type is_POD_type;
};

template<>
struct __type_traits<double>
{
    typedef __true_type has_trivial_default_constructor;
    typedef __true_type has_trivial_copy_constructor;
    typedef __true_type has_trivial_assignment_operator;
    typedef __true_type has_trivial_destructor;
    typedef __true_type is_POD_type;
};

template<>
struct __type_traits<char>
{
    typedef __true_type has_trivial_default_constructor;
    typedef __true_type has_trivial_copy_constructor;
    typedef __true_type has_trivial_assignment_operator;
    typedef __true_type has_trivial_destructor;
    typedef __true_type is_POD_type;
};
//...

template <class ForwardIterator,class T>
inline void destroy(ForwardIterator first,ForwardIterator last)
{
    typedef typename __type_traits<T>:://是不是编译器的原因，我这里::之后会出现成员的

}

int main() 
{

    system("pause");
    return 0; 
}

[we_sky2008]

[Quote=引用 2 楼 noein115 的回复:]
没编译...

destroy函数是在另外一个 construct.h 头文件里写的..
[/Quote]
呵呵，找到原因就好了，

[qq120848369]

楼主写错了,你需要的是iterator_traits,你的destroy无法识别T类型是什么,模板函数是自动推导的.

要停电了,凑活看

#include <iostream> 
#include <vector>

using namespace std; 

struct __true_type
{

};

struct __false_type
{

};

template<class T>
struct __type_traits
{
    typedef __false_type has_trivial_default_constructor;
    typedef __false_type has_trivial_copy_constructor;
    typedef __false_type has_trivial_assignment_operator;
    typedef __false_type has_trivial_destructor;
    typedef __false_type is_POD_type;
};

template<>
struct __type_traits<int>
{
    typedef __true_type has_trivial_default_constructor;
    typedef __true_type has_trivial_copy_constructor;
    typedef __true_type has_trivial_assignment_operator;
    typedef __true_type has_trivial_destructor;
    typedef __true_type is_POD_type;
};

class A;

template<>
struct __type_traits<A>
{
    typedef __true_type has_trivial_default_constructor;
    typedef __true_type has_trivial_copy_constructor;
    typedef __true_type has_trivial_assignment_operator;
    typedef __false_type has_trivial_destructor;
    typedef __true_type is_POD_type;
};

class A
{
public:
	A():p(new int(3))
	{
	}

	~A()
	{
		cout<<"You know"<<endl;
		delete p;
	}

private:
	int *p;
};


template <class T>
void destroy(T &obj)
{
	_destroy(obj,typename __type_traits<T>::has_trivial_destructor());
}

template <class T>
void _destroy(T &obj,__true_type)
{
	//do nothing
}

template <class T>
void _destroy(T &obj,__false_type)
{
	obj.~T();
}

int main() 
{
	int *p=(int*)malloc(sizeof(int));
	*p=2;
	destroy(*p);
	free(p);

	A *q=(A*)malloc(sizeof(A));
	q=new (q) A();
	destroy(*q);
	free(q);

    return 0; 
}

.