如何检测类型是迭代器还是const_iterator [英] how to detect if a type is an iterator or const_iterator

问题描述

我想知道，如果有一种方法来检查在编译时是否一个类型T的一些迭代器类型是一个const_iterator，或不。迭代器在迭代器和const迭代器之间定义的类型（value_type，pointer，...）有什么区别吗？

我想实现这样： / p>

  typedef std :: vector< int> T; 
 
 is_const_iterator< T :: iterator> :: value // is false 
 is_const_iterator< T :: const_iterator> :: value // is true 
  
 
 
解决方案
 C ++ 03解决方案：
 
 
 
因为没有答案似乎是正确的，这里是我尝试使用GCC：
  template< typename T& 
 struct is_const_pointer {static const bool value = false; }; 
 
 template< typename T> 
 struct is_const_pointer< const T *> {static const bool value = true; }; 
 
 template< typenameTimer> 
 struct is_const_iterator 
 {
 typedef typename std :: iterator_traits< TIterator> ::指针指针; 
 static const bool value = is_const_pointer< pointer> :: value; 
}; 
  
示例：
 code> int main（）
 {
 typedef std :: vector< int> :: iterator it_type; 
 typedef std :: vector< int> :: const_iterator const_it_type; 
 
 std :: cout<< （is_const_iterator< it_type> :: value）<< std :: endl; 
 std :: cout<< （is_const_iterator< const_it_type> :: value）<< std :: endl; 
} 
  
输出：
  0 
 1 
  
在线演示： http://ideone.com/TFYcW  
 
I'm wondering, if there is a way to check at compile time whether a type T of some iterator type is a const_iterator, or not. Is there some difference in the types that iterators define (value_type, pointer, ...) between iterators and const iterators?

I would like to achieve something like this:
typedef std::vector<int> T;

is_const_iterator<T::iterator>::value       // is false
is_const_iterator<T::const_iterator>::value // is true

解决方案
C++03 Solution:

As none of the answer seems correct, here is my attempt which is working with GCC:
template<typename T>
struct is_const_pointer { static const bool value = false; };

template<typename T>
struct is_const_pointer<const T*> { static const bool value = true; };

template <typename TIterator>
struct is_const_iterator
{
    typedef typename std::iterator_traits<TIterator>::pointer pointer;
    static const bool value = is_const_pointer<pointer>::value;
};
Example:
int main()
{
    typedef std::vector<int>::iterator it_type;
    typedef std::vector<int>::const_iterator const_it_type;

    std::cout << (is_const_iterator<it_type>::value) << std::endl;
    std::cout << (is_const_iterator<const_it_type>::value) << std::endl;
}
Output:
0
1
Online Demo : http://ideone.com/TFYcW

                        
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