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Hash_map with custom class pointers

Posted on 2004-04-12
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1,212 Views
Last Modified: 2008-02-01
Hi,

I have two classes
Id and ItemHandle

I am trying to use hash_map to instantiate them and run inserts and find. The code I looked up

class foo{
public:
hash_map<Id*, ItemHandle*> *handles2;
}
foo(){
handles2 = new hash_map<Id*, ItemHandle*>;
}

foo::somecommand(Id* something, ItemHandle* someHandlePtr){
//insert
handles2[something->getId()] = someHandleptr;

//find
ItemHandle *temp = handles2->find(something->getId();

//delete


}

but when I compile, i get the following error (for the insert)

file.cpp:70: invalid
   types `__gnu_cxx::hash_map<Id*, ItemHandle*,
   __gnu_cxx::hash<Id*>, std::equal_to<Id*>,
   std::allocator<ItemHandle*> >*[Id*]' for array
   subscript

  Thanks.

-Edward
0
Comment
Question by:edwardt
  • 5
7 Comments
 

Author Comment

by:edwardt
Comment Utility
If I do a
handles2->insert(something->getId(), someHandlePtr); i get the following error:

file.cpp:71: no
   matching function for call to `__gnu_cxx::hash_map<Id*,
   ItemHandle*, __gnu_cxx::hash<Id*>,
   std::equal_to<Id*>, std::allocator<ItemHandle*> >::
   insert(Id*, ItemHandle*&)'
/usr/include/c++/3.2/ext/hash_map:171: candidates are:
   std::pair<__gnu_cxx::hashtable<std::pair<const _Key, _Tp>, _Key, _HashFcn,
   std::_Select1st<std::pair<const _Key, _Tp> >, _EqualKey, _Alloc>::iterator,
   bool> __gnu_cxx::hash_map<_Key, _Tp, _HashFcn, _EqualKey,
   _Alloc>::insert(__gnu_cxx::hashtable<std::pair<const _Key, _Tp>, _Key,
   _HashFcn, std::_Select1st<std::pair<const _Key, _Tp> >, _EqualKey,
   _Alloc>::value_type&) [with _Key = Id*, _Tp =
   ItemHandle*, _HashFcn = __gnu_cxx::hash<Id*>,
   _EqualKey = std::equal_to<Id*>, _Alloc =
   std::allocator<ItemHandle*>]

0
 
LVL 4

Accepted Solution

by:
bkfirebird earned 400 total points
Comment Utility
first declare .....
struct eqstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return strcmp(s1, s2) == 0;
  }
};

and then use hash_map as ......
hash_map<const char*, int, hash<const char*>, eqstr> *handles2;
0
 
LVL 44

Assisted Solution

by:Karl Heinz Kremer
Karl Heinz Kremer earned 100 total points
Comment Utility
What type does your method getId() return? If it's Id, then this is your problem. You defined the hash_map with Id* and not with Id.
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Author Comment

by:edwardt
Comment Utility
bkfirebird
so you're saying that i need to initialize my hash_map with types const char* and int, instead of my custom classes?

khkremer
getId() returns Id*

-Edward
0
 

Author Comment

by:edwardt
Comment Utility
I still get the same errors when I try
handles2[getId()] = stuff;

or

handles2->insert(getId(), stuff);
0
 

Author Comment

by:edwardt
Comment Utility
I made the eqstr stuff and now I have

hash_map<const char*, Receiver*, hash<const char*>, eqstr> handles2;
       
where my hash function is based on a const char *

I have a function that I use to add things into my hash table, which is called roughly like

myfunc(receiver1, receiver1->toString().c_str());
myfunc(receiver2, receiver2->toString().c_str());

void Foo::myfunc(Receiver *receiver, const char *str)
{
     hash_map<const char*, Receiver*, hash<const char*>, eqstr>::iterator i;


    /*
    for (i=handles2.begin(); i!=handles2.end(); i++)
    {
        const char* key = i->first;
        cout << key  << ": is what i have" <<endl;

    }
    */
   
    i = handles2.find(str);

    if (i != handles2.end())
    {
        cout<<"ERROR - already-registered address "<<str<<endl;
        assert(false);
    }
    addressBook[str] = receiver;

}

The problem is that when I pass in a new string, then my hash table's key entry automatically changes!!!!! :( ARGH!!!! That means if my first pair is

"hello", Recever1

and my second pair that i pass in is

"hello2", Receiver2

then it changes my original hash value from "hello" to "hello2"......

Thanks.

-Edward
0
 

Author Comment

by:edwardt
Comment Utility
Hi,

The basic problem I'm having is that I need to store hashes as
hashtable[someitem->toString().c_str()] = value;

where the result of .c_str() is lets say, "mykey"
but i need to access them elsewhere using something like

hashtable.find("mykey");

Right now, it doesn't seem to work, because my hash table (i think) stores the address of c_str() instead of a literal (which I want). Anyway to convert string to a string literal :P?

Thanks.

-Edward
0

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