# hashtable

**Repository Path**: mirrors_minad/hashtable

## Basic Information

- **Project Name**: hashtable
- **Description**: Hashtable in C with open addressing and specialization via macros
- **Primary Language**: Unknown
- **License**: MIT
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2020-09-25
- **Last Updated**: 2026-03-29

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

= Hashtable with open addressing

This library provides a simple hashtable written in C. The hashtable is stored
as a single heap allocated array. This storage scheme is good for caching, since
everything is densely packed and pointer chasing is avoided in contrast to hashtables which use linked lists.
The array will grow automatically, when the filling reaches a certain threshold.

By using macros, the library is specialized for each entry type. For example
it is possible to generate a hashset without overhead, by using entries consisting only of a key.
Arbitrary key types are supported and various hash functions are provided in link:hashfn.h[].

== Configure the hash table

At first we create the hashtable functions and datastructure for the special entry type `MyEntry`.
For optimal performance all hash functions are specialized for this entry type.

[source,c]
----
typedef struct {
    const char* k;
    int         v;
} MyEntry;

#define HASH        MyHash
#define ENTRY       MyEntry
#define PREFIX      myhash
#define KEY(e)      e->k
#define EXISTS(e)   e->k
#define KEYEQ(a, b) !strcmp(a, b)
#define HASHFN      hashString
#include "hashtable.h"
----

== Usage

[source,c]
----
int main(void) {
    MyHash h = HASH_INIT;

    MyEntry* e;

    if (myhashCreate(&h, "a", &e)) {
        printf("ENTRY CREATED\n");
        e->k = "a";
        e->v = 1;
    }

    myhashCreate(&h, "b", &e);
    e->k = "b";
    e->v = 2;

    myhashCreate(&h, "c", &e);
    e->k = "c";
    e->v = 3;

    myhashCreate(&h, "c", &e);
    e->k = "c";
    e->v = 4;

    e = myhashFind(&h, "a");
    if (e)
        printf("FOUND a %d\n", e->v);
    else
        printf("NOT FOUND a\n");

    e = myhashFind(&h, "d");
    if (e)
        printf("FOUND d %d\n", e->v);
    else
        printf("NOT FOUND d\n");

    HASH_FOREACH(myhash, f, &h)
        printf("%s %d\n", f->k, f->v);
}
----

== License

MIT (c) 2018 Daniel Mendler