Elliott Back's Blog - Latest Comments in Hashmap Implementation in C — Elliott C. Back

Re: Hashmap Implementation in C — Elliott C. Back

Joe — Tue, 20 Jan 2009 11:55:21 -0000

You hashmap overwrites existing values!

Re: Hashmap Implementation in C — Elliott C. Back

vikas — Mon, 24 Dec 2007 02:30:29 -0000

Hi Elliot,
I find the code useful..
Could you please forward me the include file so that i can do some modifications to it to serve my purpose.

Thanks...
Vikas

Re: Hashmap Implementation in C — Elliott C. Back

Kajal — Mon, 05 Nov 2007 15:11:25 -0000

Hello Elliot,

Thanks for this posting of the code. I was wondering if you could send me the include files so that I get the fully functional code. As part of my project, I am doing a study of some of the implementations for hash table for space consumption check.

Thanks.

Regards,
Kajal

Re: Hashmap Implementation in C — Elliott C. Back

Srinivas — Mon, 15 Oct 2007 22:54:08 -0000

Hi, Could you please let me know the steps to include n compile in windows ? I am using Win 32 C/C++ compiler comes with Windows SDK.

Re: Hashmap Implementation in C — Elliott C. Back

saark — Sat, 01 Sep 2007 04:03:29 -0000

Yo! You really didn't understand the various hash methods (i.e. mod, knuth, etc). I mean, you used them all in your hash function. Read some more :)

Re: Hashmap Implementation in C — Elliott C. Back

Mon, 23 Jul 2007 04:37:59 -0000

厉害,不知道你能不能看懂汉字,cool, good

Re: Hashmap Implementation in C — Elliott C. Back

kingsimba — Tue, 26 Jun 2007 01:42:19 -0000

I made a improment to your code and it's 100 times faster now. Even 40% faster than the stdext::hash_map in VC2005.

I will post my code in my blog latter tonight.

The basic idea is that:
1. hashmap_get should exit at the first encouter with an empty slot. Or else it will loop through all elements at a miss.

2. hashmap_remove should rehash the elements between the deleted element and the first empty slot after it.

3. table_size should always be two times bigger than size.
This will ensure that there will always be a empty slot not too far way. This will make hashmap_get and hashmap_remove 20 times faster in my case.

4. some other bug fixes.

Re: Hashmap Implementation in C — Elliott C. Back

art Zweiban — Wed, 11 Apr 2007 14:06:08 -0000

It's pretty cool to see everybody with interesting names demanding additional work on your part, Mr. Back.

Re: Hashmap Implementation in C — Elliott C. Back

mdiarra — Sat, 17 Mar 2007 22:45:10 -0000

Hi all,

i find this project very interesting. thanks a lot Elliot. But i need the file sync.h. can you provide it to me please.

regards

Re: Hashmap Implementation in C — Elliott C. Back

gruva — Sat, 10 Feb 2007 16:00:53 -0000

it would be better if you gave a more clear example to use the module.

Re: Hashmap Implementation in C — Elliott C. Back

tiku — Tue, 05 Dec 2006 19:43:17 -0000

Hey, thx a lot, ur code is great, it really helped me alot...but It just took me along time to figure out. but thx so much...

Re: Hashmap Implementation in C — Elliott C. Back

Collections — Sat, 25 Nov 2006 15:30:55 -0000

Java Collections Framework provides a well designed set of interfaces and classes that support operations on a collections of objects.

Re: Hashmap Implementation in C — Elliott C. Back

sunil — Fri, 14 Jul 2006 05:40:16 -0000

Hi Elliott.
The code looks good and also easly usable but the 2 include files are needed to you this code and hence makes it un-useable. pls provide me those include files as soon as possible.

Thanks
Sunil

Re: Hashmap Implementation in C — Elliott C. Back

mans — Thu, 19 Jan 2006 03:21:24 -0000

Can you please attach the sync.h file and any associated implementation file, as I can see many semaphore related calls but have no idea where to find them !

Re: Hashmap Implementation in C — Elliott C. Back

Boris — Thu, 20 Oct 2005 18:57:31 -0000

Can you give an example of how to use the iteration function?

Thanks

Re: Hashmap Implementation in C — Elliott C. Back

Elliott Back — Fri, 03 Jun 2005 20:50:05 -0000

Hey Sujay. It's not obvious, but the hashmap_put function calls hashmap_hash to find an index. Hashmap_hash uses linear probing to find the next available spot. Of course, if the hashmap is full when you call hashmap_put, a resize call will be issued. Therefore, two keys never "hash" to the same array location.

Re: Hashmap Implementation in C — Elliott C. Back

sujay — Fri, 03 Jun 2005 17:50:05 -0000

I think the put function will fail, if you have two key values generating the same hash value in the array range. (say keys "abc" and "xyz" generate a hash code of '99' in the array range 0-1024 (According to the program i think the key value will be '99'..right ??). How will this put function deal with this?? It will overwrite the existing one.

I think the solution to this is to store even the key values ("abc" or "xyz" ) in the structure hash_element, so that we can compare this while inserting and this must be unique.

Re: Hashmap Implementation in C — Elliott C. Back

Elliott Back — Thu, 05 May 2005 22:55:01 -0000

As you can tell from the datastructure, you need to be passing pointers to the object memory. If you allocate a static struct "s", to put it in the map you would call the

hashmap_put(map_t in, int key, any_t value)

method. You can think of any_t as an alias for void *: it's defined in the header somewhere, So, you'd call:

hashmap_put(in, 1337, &s;);

If s is already a pointer type, just call:

hashmap_put(in, 1337, s);

To get something out of the datastructure, again just pass a pointer:

your_struct_name s;
hashmap_get(in, 1337, &s;);

Don't forget to check the return values! All the hashmap methods should return a constant indicating success.

Re: Hashmap Implementation in C — Elliott C. Back

vinod — Thu, 05 May 2005 15:51:59 -0000

Thanks for the example.
Can we store any type of variable e.g. struture as a value ?
If yes how can I retrieve the values from the hash map.
The hashmap_get is returning me junk values.I would appreciate a code sample.

Re: Hashmap Implementation in C — Elliott C. Back

Elliott Back — Wed, 04 May 2005 21:10:39 -0000

The above code allocates a datastructure for a filesystem I wrote, allocates the blocks hashmap, which keeps track of all the physical blocks of memory we can use, and then I show a for loop which puts the blocks into the hashmap indexed by the current length of the hashmap, i.e. 0, 1, ... , n. This way I end up with a hashmap of all the blocks currently in use in the filesystem (upon load).

Re: Hashmap Implementation in C — Elliott C. Back

Elliott Back — Wed, 04 May 2005 21:08:36 -0000

struct minifile {
    /* Other blocks */
    map_t blocks;
};

typedef struct minifile* minifile_t;

...

// Allocate a file
file = (minifile_t) malloc(sizeof(struct minifile));
if(!file) return NULL;

// Initialize blocks
file->blocks = hashmap_new();
if (!file->blocks) return NULL;

...

/* Get blocks */
for(i = 0; i < num_blocks; i++){
    int *temp = (int *) malloc(sizeof(1));
    *temp = *inode; inode++;
    if(hashmap_put(file->blocks, hashmap_length(file->blocks), temp) != MAP_OK)
    return NULL;
}

Re: Hashmap Implementation in C — Elliott C. Back

vinod — Wed, 04 May 2005 18:05:34 -0000

can you send me sample example on how to use this hashmap ?