Help with hash_map

Hi,

I need some help with using the hash_map.

Here is my code of declaration of my hash_map:

Code:

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hash_map<const string, Contact*> namehash;

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Contact is a class defined by myself

Here is the usage of the hash_map:

Code:

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namehash[v[c].Name()] = &v[c];

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v is a vector of Contact, Name() returns a std::string
So what's wrong with this? Just can't compile it. I included the necessary headers already, and I'm using the SGI STL.

Thanks in advance.

The compiler error may help.

Code:

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536 c:\dev-c_~1\include\g__~1\stl_hashtable.h
 instantiated from `hashtable<pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *>,const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,hash<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > >,_Select1st<pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *> >,equal_to<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > >,allocator<Contact *> >::_M_bkt_num(const pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *> &, unsigned int) const'

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Code:

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930 c:\dev-c_~1\include\g__~1\stl_hashtable.h
 instantiated from `hashtable<pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *>,const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,hash<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > >,_Select1st<pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *> >,equal_to<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > >,allocator<Contact *> >::resize(unsigned int)'

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Code:

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744 c:\dev-c_~1\include\g__~1\stl_hashtable.h
 instantiated from `hashtable<pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *>,const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,hash<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > >,_Select1st<pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *> >,equal_to<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > >,allocator<Contact *> >::find_or_insert(const pair<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >,Contact *> &)'

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Code:

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181 c:\dev-c_~1\include\g__~1\stl_hash_map.h
 instantiated from here

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Code:

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531 c:\dev-c_~1\include\g__~1\stl_hashtable.h
 no match for call to `(const hash<const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > >) (const basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> > &)'

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Does this help? So lengthy... So cryptic...

Hmm okay maybe not :).

I have no idea, then.

[edit]
What is the exact type .Name() returns?

Something to do with this?
http://forums.devshed.com/c-programm...ing-55093.html
[/edit]

.Name() returns a std::string. So I guess the "fix" in the link you gave me is of no use because of this...

Checking SGI's documentation, one of the requirements for the hash_map is that the key type is assignable. This is not the case for a const string. Perhaps you should declare it as:

Code:

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hash_map<string, Contact*> namehash;

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By the way, you may want to consider using a std::tr1::unordered_map instead of SGI's extension.

i actually tried this way first, but isn't working...

Quote:

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Originally Posted by jasperleeabc

i actually tried this way first, but isn't working...

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Well, I have never used SGI's hash_map, but the same syntax works with g++ 4.2.4's TR1 implementation:

Code:

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

class Contact
{
public:
    std::string Name() const
    {
        return Name_;
    }
private:
    std::string Name_;
};

using namespace std;

int main()
{
    vector<Contact> v(1);
    vector<Contact>::size_type c = 0;
    tr1::unordered_map<string, Contact*> namehash;
    namehash[v[c].Name()] = &v[c];
}

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You might as well switch to TR1's unordered_map since it will be included in more or less the same form in C++0x's standard library.

thanks, but I actually simply changed the string to const char* :P. Anyway, I need some other help now. Somehow, my use of the hash doesn't work...

Declaration:

Code:

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hash_map<const char*, Contact*> namehash;

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Usage:

Code:

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char* t = (char*) ListBox_GetItemData(handle, s);

*namehash[t].write(dialog);

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Compilation error:

Code:

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427 jphonebookmain.cpp
 request for member `write' in `namehash.hash_map<const char *,Contact *,hash<const char *>,equal_to<const char *>,allocator<Contact *> >::operator []((&t))', which is of non-aggregate type `Contact *'

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Anyone have any idea what's going on?

Thanks in advance.

Got it done. Problem solved already... I forgot to put the brackets around *namehash[t] ......

Quote:

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Originally Posted by jasperleeabc

but I actually simply changed the string to const char* :P

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Unfortunately, that may only be a partial solution since you would not be taking full advantage of what C++ has to offer.

Quote:

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Originally Posted by jasperleeabc

Problem solved already... I forgot to put the brackets around *namehash[t]

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Typically, we would write: namehash[t]->write(dialog);

oh yes, ->....... what was I thinking.......