A standalone and lightweight C library
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lua change to 0 indexed array Jun 4, 2011
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.gitignore Add kputw() and kputl() tests Jul 22, 2013
README.md README formatting Jun 2, 2017
bgzf.c minor changes Oct 28, 2011
bgzf.h improved backward compatibility Oct 28, 2011
kalloc.c find the largest chunk of free memory Jan 19, 2018
kalloc.h find the largest chunk of free memory Jan 19, 2018
kavl.h fixed insert counting err; couting with del Jun 18, 2018
kbit.h some basic bit operations Apr 8, 2012
kbtree.h added Sep 29, 2015
kdq.h added dequeue Aug 22, 2016
keigen.c Eigenvalues for dense symmetric matrices May 11, 2018
keigen.h Eigenvalues for dense symmetric matrices May 11, 2018
ketopt.h revert to a single-header library Aug 30, 2018
kexpr.c kexpr: evaluate by return type Aug 16, 2016
kexpr.h kexpr: evaluate by return type Aug 16, 2016
kgraph.h Graph related routines. Unfinished. DON'T USE! Dec 28, 2011
khash.h fix spelling mistake Oct 23, 2015
khmm.c Added the khmm library Jan 13, 2011
khmm.h Added the khmm library Jan 13, 2011
klist.h Prevent unused function warnings in khash.h, klist.h Jul 23, 2015
kmath.c removed MT19937-64. Aug 31, 2018
kmath.h removed MT19937-64. Aug 31, 2018
knetfile.c Don't call freeaddrinfo() when getaddrinfo() fails Jul 23, 2015
knetfile.h Added the knetfile library Jan 13, 2011
knhx.c Fixed output bug where branch length is not printed on branches to le… Jun 26, 2015
knhx.h print tree in the Newick format Dec 19, 2012
kopen.c Don't call freeaddrinfo() when getaddrinfo() fails Jul 23, 2015
krng.h Added a version of xoroshiro128+ Aug 31, 2018
ksa.c Constructing suffix array for multi-sentinel str. Aug 19, 2011
kseq.h Adds checks for failed reads and gzip files with corrupt crc. Jan 19, 2017
kson.c kson_query() -> kson_by_path() for clarity Nov 30, 2014
kson.h kson_query() -> kson_by_path() for clarity Nov 30, 2014
ksort.h Update ksort.h Nov 30, 2013
kstring.c Fix undefined behaviour and sign extension issues in kstrtok Jan 11, 2018
kstring.h Add kgetline() to kstring.c/.h Jul 23, 2015
ksw.c bugfix: point address changes Feb 21, 2013
ksw.h added NW and SW-extension; backported from bwa Feb 12, 2013
kthread.c use long for forpool Mar 4, 2017
kthread.h kt_for with a mini thread pool; buggy Dec 16, 2016
kurl.c default to following redirect & no SSL certificate Nov 28, 2014
kurl.h allow to feed change key/secret/id-file Nov 21, 2013
kvec.h Two bugs reported by istreeter and wanghc78 Jan 26, 2013


Klib: a Generic Library in C


Klib is a standalone and lightweight C library distributed under MIT/X11 license. Most components are independent of external libraries, except the standard C library, and independent of each other. To use a component of this library, you only need to copy a couple of files to your source code tree without worrying about library dependencies.

Klib strives for efficiency and a small memory footprint. Some components, such as khash.h, kbtree.h, ksort.h and kvec.h, are among the most efficient implementations of similar algorithms or data structures in all programming languages, in terms of both speed and memory use.

A new documentation is available here which includes most information in this README file.

Common components

Components for more specific use cases


For the implementation of generic containers, klib extensively uses C macros. To use these data structures, we usually need to instantiate methods by expanding a long macro. This makes the source code look unusual or even ugly and adds difficulty to debugging. Unfortunately, for efficient generic programming in C that lacks template, using macros is the only solution. Only with macros, we can write a generic container which, once instantiated, compete with a type-specific container in efficiency. Some generic libraries in C, such as Glib, use the void* type to implement containers. These implementations are usually slower and use more memory than klib (see this benchmark).

To effectively use klib, it is important to understand how it achieves generic programming. We will use the hash table library as an example:

#include "khash.h"
KHASH_MAP_INIT_INT(m32, char)        // instantiate structs and methods
int main() {
    int ret, is_missing;
    khint_t k;
    khash_t(m32) *h = kh_init(m32);  // allocate a hash table
    k = kh_put(m32, h, 5, &ret);     // insert a key to the hash table
    if (!ret) kh_del(m32, h, k);
    kh_value(h, k) = 10;             // set the value
    k = kh_get(m32, h, 10);          // query the hash table
    is_missing = (k == kh_end(h));   // test if the key is present
    k = kh_get(m32, h, 5);
    kh_del(m32, h, k);               // remove a key-value pair
    for (k = kh_begin(h); k != kh_end(h); ++k)  // traverse
        if (kh_exist(h, k))          // test if a bucket contains data
			kh_value(h, k) = 1;
    kh_destroy(m32, h);              // deallocate the hash table
    return 0;

In this example, the second line instantiates a hash table with unsigned as the key type and char as the value type. m32 names such a type of hash table. All types and functions associated with this name are macros, which will be explained later. Macro kh_init() initiates a hash table and kh_destroy() frees it. kh_put() inserts a key and returns the iterator (or the position) in the hash table. kh_get() and kh_del() get a key and delete an element, respectively. Macro kh_exist() tests if an iterator (or a position) is filled with data.

An immediate question is this piece of code does not look like a valid C program (e.g. lacking semicolon, assignment to an apparent function call and apparent undefined m32 'variable'). To understand why the code is correct, let's go a bit further into the source code of khash.h, whose skeleton looks like:

#define KHASH_INIT(name, SCOPE, key_t, val_t, is_map, _hashf, _hasheq) \
  typedef struct { \
    int n_buckets, size, n_occupied, upper_bound; \
    unsigned *flags; \
    key_t *keys; \
    val_t *vals; \
  } kh_##name##_t; \
  SCOPE inline kh_##name##_t *init_##name() { \
    return (kh_##name##_t*)calloc(1, sizeof(kh_##name##_t)); \
  } \
  SCOPE inline int get_##name(kh_##name##_t *h, key_t k) \
  ... \
  SCOPE inline void destroy_##name(kh_##name##_t *h) { \
    if (h) { \
      free(h->keys); free(h->flags); free(h->vals); free(h); \
    } \

#define _int_hf(key) (unsigned)(key)
#define _int_heq(a, b) (a == b)
#define khash_t(name) kh_##name##_t
#define kh_value(h, k) ((h)->vals[k])
#define kh_begin(h, k) 0
#define kh_end(h) ((h)->n_buckets)
#define kh_init(name) init_##name()
#define kh_get(name, h, k) get_##name(h, k)
#define kh_destroy(name, h) destroy_##name(h)
#define KHASH_MAP_INIT_INT(name, val_t) \
	KHASH_INIT(name, static, unsigned, val_t, is_map, _int_hf, _int_heq)

KHASH_INIT() is a huge macro defining all the structs and methods. When this macro is called, all the code inside it will be inserted by the C preprocess to the place where it is called. If the macro is called multiple times, multiple copies of the code will be inserted. To avoid naming conflict of hash tables with different key-value types, the library uses token concatenation, which is a preprocessor feature whereby we can substitute part of a symbol based on the parameter of the macro. In the end, the C preprocessor will generate the following code and feed it to the compiler (macro kh_exist(h,k) is a little complex and not expanded for simplicity):

typedef struct {
  int n_buckets, size, n_occupied, upper_bound;
  unsigned *flags;
  unsigned *keys;
  char *vals;
} kh_m32_t;
static inline kh_m32_t *init_m32() {
  return (kh_m32_t*)calloc(1, sizeof(kh_m32_t));
static inline int get_m32(kh_m32_t *h, unsigned k)
static inline void destroy_m32(kh_m32_t *h) {
  if (h) {
    free(h->keys); free(h->flags); free(h->vals); free(h);

int main() {
	int ret, is_missing;
	khint_t k;
	kh_m32_t *h = init_m32();
	k = put_m32(h, 5, &ret);
	if (!ret) del_m32(h, k);
	h->vals[k] = 10;
	k = get_m32(h, 10);
	is_missing = (k == h->n_buckets);
	k = get_m32(h, 5);
	del_m32(h, k);
	for (k = 0; k != h->n_buckets; ++k)
		if (kh_exist(h, k)) h->vals[k] = 1;
	return 0;

This is the C program we know.

From this example, we can see that macros and the C preprocessor plays a key role in klib. Klib is fast partly because the compiler knows the key-value type at the compile time and is able to optimize the code to the same level as type-specific code. A generic library written with void* will not get such performance boost.

Massively inserting code upon instantiation may remind us of C++'s slow compiling speed and huge binary size when STL/boost is in use. Klib is much better in this respect due to its small code size and component independency. Inserting several hundreds lines of code won't make compiling obviously slower.


  • Library documentation, if present, is available in the header files. Examples can be found in the test/ directory.
  • Obsolete documentation of the hash table library can be found at SourceForge. This README is partly adapted from the old documentation.
  • Blog post describing the hash table library.
  • Blog post on why using void* for generic programming may be inefficient.
  • Blog post on the generic stream buffer.
  • Blog post evaluating the performance of kvec.h.
  • Blog post arguing B-tree may be a better data structure than a binary search tree.
  • Blog post evaluating the performance of khash.h and kbtree.h among many other implementations. An older version of the benchmark is also available.
  • Blog post benchmarking internal sorting algorithms and implementations.
  • Blog post on the k-small algorithm.
  • Blog post on the Hooke-Jeeve's algorithm for nonlinear programming.