HASH.md (4257B)
1 <!-- 2 Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3 4 SPDX-License-Identifier: curl 5 --> 6 7 # `hash` 8 9 #include "hash.h" 10 11 This is the internal module for doing hash tables. A hash table uses a hash 12 function to compute an index. On each index there is a separate linked list of 13 entries. 14 15 Create a hash table. Add items. Retrieve items. Remove items. Destroy table. 16 17 ## `Curl_hash_init` 18 19 ~~~c 20 void Curl_hash_init(struct Curl_hash *h, 21 size_t slots, 22 hash_function hfunc, 23 comp_function comparator, 24 Curl_hash_dtor dtor); 25 ~~~ 26 27 The call initializes a `struct Curl_hash`. 28 29 - `slots` is the number of entries to create in the hash table. Larger is 30 better (faster lookups) but also uses more memory. 31 - `hfunc` is a function pointer to a function that returns a `size_t` value as 32 a checksum for an entry in this hash table. Ideally, it returns a unique 33 value for every entry ever added to the hash table, but hash collisions are 34 handled. 35 - `comparator` is a function pointer to a function that compares two hash 36 table entries. It should return non-zero if the compared items are 37 identical. 38 - `dtor` is a function pointer to a destructor called when an entry is removed 39 from the table 40 41 ## `Curl_hash_add` 42 43 ~~~c 44 void * 45 Curl_hash_add(struct Curl_hash *h, void *key, size_t key_len, void *p) 46 ~~~ 47 48 This call adds an entry to the hash. `key` points to the hash key and 49 `key_len` is the length of the hash key. `p` is a custom pointer. 50 51 If there already was a match in the hash, that data is replaced with this new 52 entry. 53 54 This function also lazily allocates the table if needed, as it is not done in 55 the `Curl_hash_init` function. 56 57 Returns NULL on error, otherwise it returns a pointer to `p`. 58 59 ## `Curl_hash_add2` 60 61 ~~~c 62 void *Curl_hash_add2(struct Curl_hash *h, void *key, size_t key_len, void *p, 63 Curl_hash_elem_dtor dtor) 64 ~~~ 65 66 This works like `Curl_hash_add` but has an extra argument: `dtor`, which is a 67 destructor call for this specific entry. When this entry is removed, this 68 function is called instead of the function stored for the whole hash table. 69 70 ## `Curl_hash_delete` 71 72 ~~~c 73 int Curl_hash_delete(struct Curl_hash *h, void *key, size_t key_len); 74 ~~~ 75 76 This function removes an entry from the hash table. If successful, it returns 77 zero. If the entry was not found, it returns 1. 78 79 ## `Curl_hash_pick` 80 81 ~~~c 82 void *Curl_hash_pick(struct Curl_hash *h, void *key, size_t key_len); 83 ~~~ 84 85 If there is an entry in the hash that matches the given `key` with size of 86 `key_len`, that its custom pointer is returned. The pointer that was called 87 `p` when the entry was added. 88 89 It returns NULL if there is no matching entry in the hash. 90 91 ## `Curl_hash_destroy` 92 93 ~~~c 94 void Curl_hash_destroy(struct Curl_hash *h); 95 ~~~ 96 97 This function destroys a hash and cleanups up all its related data. Calling it 98 multiple times is fine. 99 100 ## `Curl_hash_clean` 101 102 ~~~c 103 void Curl_hash_clean(struct Curl_hash *h); 104 ~~~ 105 106 This function removes all the entries in the given hash. 107 108 ## `Curl_hash_clean_with_criterium` 109 110 ~~~c 111 void 112 Curl_hash_clean_with_criterium(struct Curl_hash *h, void *user, 113 int (*comp)(void *, void *)) 114 ~~~ 115 116 This function removes all the entries in the given hash that matches the 117 criterion. The provided `comp` function determines if the criteria is met by 118 returning non-zero. 119 120 ## `Curl_hash_count` 121 122 ~~~c 123 size_t Curl_hash_count(struct Curl_hash *h) 124 ~~~ 125 126 Returns the number of entries stored in the hash. 127 128 ## `Curl_hash_start_iterate` 129 130 ~~~c 131 void Curl_hash_start_iterate(struct Curl_hash *hash, 132 struct Curl_hash_iterator *iter): 133 ~~~ 134 135 This function initializes a `struct Curl_hash_iterator` that `iter` points to. 136 It can then be used to iterate over all the entries in the hash. 137 138 ## `Curl_hash_next_element` 139 140 ~~~c 141 struct Curl_hash_element * 142 Curl_hash_next_element(struct Curl_hash_iterator *iter); 143 ~~~ 144 145 Given the iterator `iter`, this function returns a pointer to the next hash 146 entry if there is one, or NULL if there is no more entries. 147 148 Called repeatedly, it iterates over all the entries in the hash table. 149 150 Note: it only guarantees functionality if the hash table remains untouched 151 during its iteration.