Solved

Hash_map with custom class pointers

Posted on 2004-04-12
7
1,214 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
ID: 10807671
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
ID: 10807825
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
ID: 10807880
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.
0
Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

 

Author Comment

by:edwardt
ID: 10817191
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
ID: 10817301
I still get the same errors when I try
handles2[getId()] = stuff;

or

handles2->insert(getId(), stuff);
0
 

Author Comment

by:edwardt
ID: 10818782
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
ID: 10819141
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

Featured Post

Active Directory Webinar

We all know we need to protect and secure our privileges, but where to start? Join Experts Exchange and ManageEngine on Tuesday, April 11, 2017 10:00 AM PDT to learn how to track and secure privileged users in Active Directory.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

This article will show you some of the more useful Standard Template Library (STL) algorithms through the use of working examples.  You will learn about how these algorithms fit into the STL architecture, how they work with STL containers, and why t…
Go is an acronym of golang, is a programming language developed Google in 2007. Go is a new language that is mostly in the C family, with significant input from Pascal/Modula/Oberon family. Hence Go arisen as low-level language with fast compilation…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

821 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question