Looking for a good hash table implementation in C

Question

I am primarily interested in string keys. Can someone point me towards a library?

score 61 · Answer 1 · edited Jun 21 '13 at 17:13

I had the same need and did some research and ended up using libcfu

It's simple and readable so if I have a need to modify, I can do it without spending too much time to understand. It's also of BSD license. No need to change my structs (to embed say a next pointer)

I had to reject the other options for following reasons (my personal reasons, YMMV):

sglib --> it's a macro maze and I wasn't comfortable debugging/making changes on such a code base using just macros
cbfalconer --> lot of licensing redflags, and the site was down and too many unfavorable discussions on web about support/author; didn't want to take the risk
google sparce-hash --> as stated already, it's for C++, not C
glib (gnome hash) --> looked very promising; but I couldn't find any easy way to install the developer kit; I just needed the C routines/files -- not the full blown developement environment
Judy --> seems too complex for a simple use.. also was not ready to debug myself if I had to run into any issues
npsml (mentioned here) --> can't find the source
strmap found very simple and useful -- it's just too simplistic that both key and value must be strings; value being string seems too restrictive (should accept void *)
uthash --> seems good (has been mentioned on wikipedia on hashtable); found that it requires struct to be modified -- didn't want to do that as performace is not really a concern for my use --it's more of development velocity.

In summary for very simple use strmap is good; uthash if you are concerned with additional memory use. If just speed of development or ease of use is primary objective, libcfu wins [note libcfu internally does memory allocation to maintain the nodes/hashtables]. It's surprising that there aren't many simple C hash implementations available.

i notice uthash seems to be more actively developed than libcfu (2005 vintage). perhaps this isn't an issue for a small bit of code though - have you come across any other contenders since this post? — bph, Jan 23 '12 at 10:27
I have a huge dataset, and glib does not support that big data (32-bit keys). I need more than glib. How about libcfu? — Baskaya, Feb 25 '13 at 19:14
The hashtable implementation in CPython is based on libcfu: https://github.com/python/cpython/blob/master/Modules/hashtable.c — Ryan Li, Jul 02 '15 at 18:04
Libcfu 's document: http://libcfu.sourceforge.net/libcfu.html — Zhou Hongbo, Jun 02 '22 at 07:49
Finally I choose UTHash on Android. Some notes: if occured `fall-through between switch labels`, please use `#pragma GCC diagnostic ignored "-Wimplicit-fallthrough"`; if occured `padding struct 'struct UT_hash_table' with 4 bytes to align 'tail'`, see https://github.com/troydhanson/uthash/issues/118#issue-223582662 — Zhou Hongbo, Jun 15 '22 at 09:20

score 16 · Answer 2 · edited Apr 06 '11 at 15:39

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GLib is a great library to use as a foundation in your C projects. They have some decent data structure offerings including Hash Tables: http://developer.gnome.org/glib/2.28/glib-Hash-Tables.html (link updated 4/6/2011)

edited Apr 06 '11 at 15:39

Andrew Parsons

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answered Jul 16 '09 at 16:56

Daniel M

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+1: Glib is indeed a great library. – Stefano Borini Jul 17 '09 at 01:24
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am i right in thinking you usually dynamically link to the glib library to use these data structures, potentially creating porting issues if moving from linux to windows? – bph Jan 23 '12 at 10:35
Glib supports only 32-bit. If you work with huge data, glib won't be a good choice – Baskaya Feb 25 '13 at 19:10

nik · Answer 3 · 2009-07-16T16:38:00.677

For strings, the Judy Array might be good.

A Judy array is a complex but very fast associative array data structure for storing and looking up values using integer or string keys. Unlike normal arrays, Judy arrays may be sparse; that is, they may have large ranges of unassigned indices.

Here is a Judy library in C.

A C library that provides a state-of-the-art core technology that implements a sparse dynamic array. Judy arrays are declared simply with a null pointer. A Judy array consumes memory only when it is populated, yet can grow to take advantage of all available memory if desired.

Other references,
This Wikipedia hash implementation reference has some C open source links.
Also, cmph -- A Minimal Perfect Hashing Library in C, supports several algorithms.

score 5 · Answer 4 · edited May 23 '17 at 12:25

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There are some good answers here:
Container Class / Library for C

http://sglib.sourceforge.net.
http://cbfalconer.home.att.net/download/

edited May 23 '17 at 12:25

Community

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answered Jul 16 '09 at 16:43

Nick Van Brunt

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score 5 · Answer 5 · answered Jul 17 '09 at 01:16

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Dave Hanson's C Interfaces and Implementations includes a fine hash table and several other well-engineered data structures. There is also a nice string-processing interface. The book is great if you can afford it, but even if not, I have found this software very well designed, small enough to learn in its entirety, and easy to reuse in several different projects.

answered Jul 17 '09 at 01:16

Norman Ramsey

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Dang! I need to buy this! – kirbyfan64sos Oct 02 '15 at 22:50

score 5 · Answer 6 · answered Mar 28 '11 at 16:23

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A long time has passed since I asked this question... I can now add my own public domain library to the list:

http://sourceforge.net/projects/npsml/

answered Mar 28 '11 at 16:23

Setjmp

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score 4 · Answer 7 · answered Jul 16 '09 at 16:52

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C Interfaces and Implementations discusses hash table implementations in C. The source code is available online. (My copy of the book is at work so I can't be more specific.)

answered Jul 16 '09 at 16:52

sblair

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Thanks for introducing this book. Just placed an order in Amazon. – Qiang Xu Jan 04 '13 at 21:11

score 3 · Answer 8 · answered Feb 11 '13 at 22:34

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Apache's APR library has its own hash-implementation. It is already ported to anything Apache runs on and the Apache license is rather liberal too.

answered Feb 11 '13 at 22:34

Mikhail T.

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This looks to be a really practical choice for C programming. It has everything, widely used and tested, well documented, .. – minghua Sep 14 '13 at 14:23

score 3 · Answer 9 · answered Apr 25 '13 at 19:45

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khash.h from samtools/bwa/seqtk/klib

curl https://raw.github.com/attractivechaos/klib/master/khash.h

via http://www.biostars.org/p/10353/

answered Apr 25 '13 at 19:45

alex

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although khash looks like it's written to be very efficient, one thing it lacks is documentation/an toy example of it in use... – Andy Hayden Oct 11 '13 at 22:32
there are examples here http://www.biostars.org/p/10353/ – alex Oct 13 '13 at 16:36
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I see one example, which doesn't offer any explanation and similar to the docs it has one letter non-descriptive variable names and no comments. It's annoying as no doubt it's doing something straightforward. – Andy Hayden Oct 13 '13 at 18:02

score 2 · Answer 10 · answered Jul 16 '09 at 16:29

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Never used it but Google Sparsehash may work

answered Jul 16 '09 at 16:29

Nick

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I thought that sparsehase written in C++. – Kirill V. Lyadvinsky Jul 16 '09 at 16:37
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Indeed, C is the language of interest in this case--not C++. – Setjmp Jul 17 '09 at 00:37

score 2 · Answer 11 · answered Jul 16 '09 at 16:45

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Download tcl and use their time-proven tcl hash function. It's easy. The TCL API is well documented.

answered Jul 16 '09 at 16:45

xcramps

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score 0 · Answer 12 · edited Nov 21 '19 at 08:04

https://github.com/dozylynx/C-hashtable

[updated URL as original now 404s: http://www.cl.cam.ac.uk/~cwc22/hashtable/ ]

Defined functions

* create_hashtable
* hashtable_insert
* hashtable_search
* hashtable_remove
* hashtable_count
* hashtable_destroy

Example of use

  struct hashtable  *h;
  struct some_key   *k;
  struct some_value *v;

  static unsigned int         hash_from_key_fn( void *k );
  static int                  keys_equal_fn ( void *key1, void *key2 );

  h = create_hashtable(16, hash_from_key_fn, keys_equal_fn);

  insert_key   = (struct some_key *) malloc(sizeof(struct some_key));
  retrieve_key = (struct some_key *) malloc(sizeof(struct some_key));

  v = (struct some_value *) malloc(sizeof(struct some_value));

  (You should initialise insert_key, retrieve_key and v here)

  if (! hashtable_insert(h,insert_key,v) )
  {     exit(-1);               }

  if (NULL == (found = hashtable_search(h,retrieve_key) ))
  {    printf("not found!");                  }

  if (NULL == (found = hashtable_remove(h,retrieve_key) ))
  {    printf("Not found\n");                 }

  hashtable_destroy(h,1); /* second arg indicates "free(value)" */

I am the author of the above hash table. The code is available at: https://github.com/dozylynx/C-hashtable — xtopher, Nov 21 '19 at 04:31

score 0 · Answer 13 · answered Jul 16 '09 at 21:47

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Gperf - Perfect Hash Function Generator

http://www.ibm.com/developerworks/linux/library/l-gperf.html

answered Jul 16 '09 at 21:47

Ryan Christensen · Answer 14 · 2012-05-17T10:33:30.223

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stl has map and hash_map (hash_map is only in some implementations) that are key to value if you are able to use C++.

http://www.cplusplus.com/reference/stl/map/

edited May 17 '12 at 10:33

answered Mar 27 '11 at 17:44

Ryan Christensen

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Looking for a good hash table implementation in C

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