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There is no standard implementation of associative arrays in C, but a 3rd-party library, C Hash Table, with BSD license, is available. [1] Another 3rd-party library, uthash, also creates associative arrays from C structures. A structure represents a value, and one of the structure fields serves as the key. [2]
The most frequently used general-purpose implementation of an associative array is with a hash table: an array combined with a hash function that separates each key into a separate "bucket" of the array. The basic idea behind a hash table is that accessing an element of an array via its index is a simple, constant-time operation.
For example, a priority queue is often implemented as a heap, while an associative array is often implemented as a hash table, so these abstract types are often referred to by this preferred implementation, as a "heap" or a "hash", though this is incorrect conceptually.
In the following table: first – the index of the first element in the slice; last – the index of the last element in the slice; end – one more than the index of last element in the slice; len – the length of the slice (= end - first) step – the number of array elements in each (default 1)
In the hash table implementation of associative arrays, an array of length is partially filled with elements, where . A key x {\displaystyle x} is hashed using a hash function h {\displaystyle h} to compute an index location A [ h ( x ) ] {\displaystyle A[h(x)]} in the hash table, where h ( x ) < m {\displaystyle h(x)<m} .
As a single concrete data structure may be used to implement many abstract data types, some data structures may appear in multiple comparisons (for example, a hash map can be used to implement an associative array or a set).
The disadvantage of association lists is that the time to search is O(), where n is the length of the list. [3] For large lists, this may be much slower than the times that can be obtained by representing an associative array as a binary search tree or as a hash table.
The implementation of methods is usually provided in a separate source file, with the following syntax type class :: foo ( «parameters» ) { instructions } [ 33 ] void foo ( «parameters» ) { instructions }