I am hitting a problem with std::list and std::map. In this post, I
have a simple (I hope) example of this.
I attempted this template function, whose purpose is to search a list,
where "list" is one of the standard containers in the C++ STL
(standard template library).
template <typename T>
std::list::const_iterator<T> xfind (
const std::list<T>& my_list, const T& candidate)
{
std::list<T>::const_iterator list_iterator;
for (list_iterator = my_list.begin() ; list_iterator != my_list.end() ;
++list_iterator)
{
if (*list_iterator == candidate) break;
}
return list_iterator;
}
Fail! the compiler barfs on the line
std::list::const_iterator<T> xfind (
It complains
parse_register_txt.cc:32: error: 'template<class _Tp, class _Alloc>
class std::list' used without template parameters
parse_register_txt.cc:32: error: expected constructor, destructor, or
type conversion before '<' token
I think I know what the problem is. The g++ implementation of "list"
includes this:
template<typename _Tp, typename _Alloc = std::allocator<_Tp> >
class list : protected _List_base<_Tp, _Alloc>
{
.
.
.
typedef _List_const_iterator<_Tp> const_iterator;
.
.
.
};
In other words, std::list::const_iterator is implemented as an entity
_List_const_iterator that is in the std namespace. Using this insight,
I can get the compiler to accept this:
template <typename T>
std::_List_const_iterator<T> xfind (
const std::list<T>& my_list, const T& candidate)
{
std::_List_const_iterator<T> list_iterator;
for (list_iterator = my_list.begin() ; list_iterator != my_list.end() ;
++list_iterator)
{
if (*list_iterator == candidate) break;
}
return list_iterator;
}
I find this to be unsatisfying. I am concerned that _List_const_iterator
may be a non-portable feature of gcc.
Is there a better way?
--
David Arnstein (00)
arnstein+use...@pobox.com {{ }}
^^
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