6 +-----------+--------------------+---------------------------------------+
7 | Operation | Average complexity | Notes |
8 +-----------+--------------------+-------------------------------------- +
10 | Append | O(1) | unpredictable if capacity is exceeded |
11 | Insert | O(n) | unpredictable if capacity is exceeded |
12 | Sort | O(n log n) | |
14 +-----------+--------------------+---------------------------------------+
16 An array is a data structure where all elements (members) have the same size and are
17 located consecutively in memory.
19 Each array has a size which holds the number of current elements of the array.
20 It also has a capacity, which is the number of elements that currently fit into
21 the array, which may be bigger than size.
23 The lookup complexity is O(1), which makes arrays well suited for fast lookups.
25 The complexity for appending an element at the end of the array is O(1).
27 The complexity for inserting an element at an arbitrary index of the array is O(n),
28 where n is the length of the array. This is because memory may need to be moved.
30 However, the insert/append complexity becomes unpredictable and largely depends on
31 the implementation of the C library if the capacity is exceeded. If the capacity
32 needs to be extended, the memory is reallocated. The mentioned complexity rules
33 only apply as long as (cap > siz + 1). *Usually*, realloc will have a complexity
34 of either O(1), if the memory block happens to be already big enough, or
35 O(n) + X, if a new, bigger block needs to be allocated and the memory copied.
37 Note that when the capacity is extended, it is possible to allocated more space space
38 than needed, to prevent frequent calls to append/insert from having to reallocate
39 the memory every time. If, and if yes how much additional space is allocated is
40 determined by the extra space field. Extra space for ext elements is allocated
41 whenever a growth reallocation happens.
43 The array can be sorted. In this case, the array is expected to have a comparator cmp
46 The comparison function must return an integer less than, equal to, or greater than
47 zero if the first argument is considered to be respectively less than, equal to,
48 or greater than the second. If two members compare as equal, their order in the
49 sorted array is undefined. [Copied from the Linux man-pages]
51 The sorting function uses the quicksort algorithm from the C library, which has an
52 average complexity of O(n log n).
54 To maintain the order of a sorted array, add and put should not be used.
57 #ifndef _DRAGONSTD_ARRAY_H_ // include guard
58 #define _DRAGONSTD_ARRAY_H_
60 #include <stddef.h> // for size_t
61 #include <sys/types.h> // for ssize_t
63 typedef int (*ArrayComparator)(const void *va, const void *vb);
68 size_t ext; // extra space
69 ArrayComparator cmp; // comparator
71 size_t mbs; // member size
72 size_t siz; // used space
73 size_t cap; // available space
76 void array_ini(Array *array, size_t mmb, size_t ext, ArrayComparator cmp);
78 Initializes the array.
80 The array will have the member size of mmb and the extra space set to ext.
81 mmb should be bigger than 0 and may not be changed after the initialization.
82 ext can be 0 or bigger and may be changed any time.
83 The comparator of the array is set to cmp and may be nil.
85 This function should be called before calling any other functions on the
88 This function should not be called on an array that has been initialized before,
89 unless the array either has a capacity of 0 or it has been deleted using
90 array_del. Otherwise a memory leak will occur.
93 void array_rlc(Array *array);
95 Reallocates the array's memory to match it's capacity.
97 This function should be called every time the capacity has changed.
100 void array_grw(Array *array, size_t n);
102 Grows the array by n bytes.
104 This function increases the arrays size by n bytes. If this exceeds the capacity of
105 the array, the capacity set to the size and the extra space ext is added to it.
107 If the capacity is changed, the array is reallocated.
109 If n is zero, the array's capacity may still grow by extra space if it exactly
110 matches the current size.
113 void array_shr(Array *array, size_t n);
115 Shrinks the array by n bytes.
117 This function decreases the arrays size by n bytes.
119 If the array has additional capacity left after it has been shrunk, the capacity
120 is set to the new size and the array is reallocated to fit the new capacity.
121 For n > 0, this is always the case, for n = 0, this may be the case.
123 Note that calling this function with n = 0 is useful to shrink the array's memory to
124 exactly fit it's used size.
127 void array_put(Array *array, const void *ptr, size_t n);
129 Grows the array by 1 and inserts ptr at the index n.
131 This function inserts the memory pointed to by ptr before the array member at
132 index n, moving all elements from that index to the end of the array.
134 After this operation, the inserted element will be _at_ the index n.
136 The memory that ptr points to, which's size is assumed to be at least as big as the
137 array's member size is copied into the arrays memory.
139 n should be in the range from 0 to the array's size.
142 void array_add(Array *array, const void *ptr);
144 Grows the array by 1 and appends ptr at the end of the array.
146 This function's result is equivalent to calling array_put(array, ptr, array->siz),
147 but it is slightly faster since it saves unnecessary calls.
150 void array_cpy(Array *array, void **ptr, size_t *n);
152 Allocates a buffer big enough to fit the array's used size.
153 Copies the array's contents into the allocated buffer.
154 Returns the buffer in ptr and the size in n.
156 Note that the returned size is the number of elements, not the number of bytes.
159 void array_cln(Array *dst, Array *src);
161 Clones the array src to the array dst.
163 dst is initialized to have the same configuration (member size, extra space,
166 After the operation, the contents of the array dst are be the same as those of src.
167 The size of dst and src are the same, the capacity of dst however is the same as
168 the size of dst and src (which might not equal the capacity of src).
170 Since array_ini is called on dst, it should be uninitialized, empty or deleted.
173 void array_rcy(Array *array);
177 This function sets the used size of the array to 0 but leaves the capacity unchanged.
178 The array's memory is not free'd and the array can be reused.
181 void array_del(Array *array);
185 This function frees the arrays memory. If this is not called when the array's
186 reference is dropped, a memory leak occurs, unless the array is empty (capacity
187 of 0), in which case the function does not need to be called. The function works
188 fine on empty arrays however.
190 After this, the array should no longer be used until reinitialized.
193 void array_srt(Array *array);
195 Sorts the array using the quicksort algorithm.
197 The array is assumed to have a non-NULL comparator.
198 Wraps the qsort C-library routine. Please refer to it's documentation.
201 ssize_t array_fnd(Array *array, const void *ptr, size_t *idx);
203 Searches the sorted array for the element ptr.
204 Returns the index of the element, or -1 if it wasn't found.
206 If idx is not NULL, a pointer to the last searched index is saved to where it
207 points to. This is the index ptr would need to be inserted at to keep the order.
209 It is assumed that the array has been sorted by array_srt before (or was empty),
210 and the order has been kept and the comparator has not been changed since.
213 size_t array_ins(Array *array, const void *ptr);
215 Inserts an element into a sorted array, keeping the order.
216 Returns the index the element has been inserted at.
218 Calls array_fnd and array_put.
220 It is assumed that the array has been sorted by array_srt before (or was empty),
221 and the order has been kept and the comparator has not been changed since.
224 #endif // _DRAGONSTD_ARRAY_H_