Re: error with tr1 unordered_map iterator

From:

"Emmanuel Deloget" <logout@free.fr>

Newsgroups:

comp.lang.c++

Date:

28 Feb 2007 08:52:31 -0800

Message-ID:

<1172681551.256849.46720@a75g2000cwd.googlegroups.com>

On 28 f=E9v, 00:07, Rares Vernica <rvern...@gmail.com> wrote:

Piyo wrote:

Rares Vernica wrote:

Hi,

I am using tr1/unordered_map in my code.

My code compiled ok on g++ (GCC) 4.1.2 (Ubuntu 4.1.2-0ubuntu1). Now I
need to compile my code on g++ (GCC) 4.0.3 (Ubuntu 4.0.3-1ubuntu5).

I get a messy error. Here are what I try to do:

typedef unordered_map<string, unsigned> StringHash;
...
StringHash::const_iterator word_pos;

I get the error when I create the const_iterator:

index.cc:161: error: no matching function for call to
'Internal::hashtable_iterator<std::pair<const std::basic_string<char,
std::char_traits<char>, std::allocator<char> >, unsigned int>, true,
false>::hashtable_iterator()'

Removing const from the iterator does not make any difference.

I tried to add const to string:

typedef unordered_map<const string, unsigned> StringHash;
...
typedef set<unsigned> WordLevelEntrySet;
typedef pair<StringHash::const_iterator, WordLevelEntrySet>
WordLevelEntry;

And the error moves to another place but is also on const_iterator:

/usr/lib/gcc/i486-linux-gnu/4.0.3/../../../../include/c++/4.0.3/tr1/ha=

shtable:

In instantiation of 'Internal::hash_code_base<const
std::basic_string<char, std::char_traits<char>, std::allocator<char>

, std::pair<const std::basic_string<char, std::char_traits<char>,

std::allocator<char> >, unsigned int>,
Internal::extract1st<std::pair<const std::basic_string<char,
std::char_traits<char>, std::allocator<char> >, unsigned int> >,
std::equal_to<const std::basic_string<char, std::char_traits<char>,
std::allocator<char> > >, std::tr1::hash<const std::basic_string<char,
std::char_traits<char>, std::allocator<char> > >,
Internal::mod_range_hashing, Internal::default_ranged_hash, false>':

Is probably something that has been fixed or improved between the
versions. Is there any workaround?

Thanks a lot,
Ray

Woah this is way odd but based on my tests,
unordered_map::iterator has no default constructor.
This is what you seem to be encountering. I am not
sure if that is a bug on G++'s part or not or if
TR1 specifies that it need not be default constructible.

--------------------------------------------------------
#include <tr1/unordered_map>
#include <string>

using namespace std;
using namespace std::tr1;
typedef unordered_map<string, unsigned> StringHash;

int
main()
{
    StringHash myHashTable;
    // assume you added some stuff in it

    StringHash::const_iterator iter( myHashTable.begin() );

}

Yes, it seems that the iterator does not have a default constructor.

I hope I am wrong. :)

Thanks,
Ray

The TR1 only states that the unordered_map iterators are "of at least
the forward iterator category", so I guess they have to respect the
standard requirements (which in this case means that they should have
a default constructor, as per table 74 (=A724.1.3)). I'd consider this
to be a bug in the TR1 implementation that comes with g++ (but that's
not like this implementation was complete) - unless I misundertood
something.

Regards,

-- Emmanuel Deloget