22 comments

• 

  vinod

  4 years ago

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

  Elliott Back

  4 years ago

  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;
  }
  reply
• 

  Elliott Back

  4 years ago

  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).
  reply
• 

  vinod

  4 years ago

  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.
  reply
• 

  Elliott Back

  4 years ago

  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.
  reply
• 

  sujay

  4 years ago

  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.
  reply
• 

  Elliott Back

  4 years ago

  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.
  reply
• 

  Boris

  3 years ago

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

  mans

  3 years ago

  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 !
  reply
• 

  sunil

  2 years ago

  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
  reply
• 

  Collections

  2 years ago

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

  tiku

  2 years ago

  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...
  reply
• 

  gruva

  2 years ago

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

  mdiarra

  2 years ago

  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
  reply
• 

  art Zweiban

  2 years ago

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

  kingsimba

  2 years ago

  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.
  reply
• 

  骋

  1 year ago

  厉害,不知道你能不能看懂汉字,cool, good
  reply
• 

  saark

  1 year ago

  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 :)
  reply
• 

  Srinivas

  1 year ago

  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.
  reply
• 

  Kajal

  1 year ago

  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
  reply
• 

  vikas

  1 year ago

  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
  reply
• 

  Joe

  5 months ago

  You hashmap overwrites existing values!
  reply