?
Solved

Hash_map with custom class pointers

Posted on 2004-04-12
7
Medium Priority
?
1,229 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 1200 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 300 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
What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

 

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

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

Question has a verified solution.

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

Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
Many modern programming languages support the concept of a property -- a class member that combines characteristics of both a data member and a method.  These are sometimes called "smart fields" because you can add logic that is applied automaticall…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.

621 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