5 +-----------+--------------------+---------------------------------------+
6 | Operation | Average complexity | Notes |
7 +-----------+--------------------+-------------------------------------- +
9 | Append | O(1) | unpredictable if capacity is exceeded |
10 | Insert | O(n) | unpredictable if capacity is exceeded |
11 | Sort | O(n log n) | |
13 +-----------+--------------------+---------------------------------------+
15 An array is a data structure where all elements (members) have the same size and are
16 located consecutively in memory.
18 Each array has a size which holds the number of current elements of the array.
19 It also has a capacity, which is the number of elements that currently fit into
20 the array, which may be bigger than size.
22 The lookup complexity is O(1), which makes arrays well suited for fast lookups.
24 The complexity for appending an element at the end of the array is O(1).
26 The complexity for inserting an element at an arbitrary index of the array is O(n),
27 where n is the length of the array. This is because memory may need to be moved.
29 However, the insert/append complexity becomes unpredictable and largely depends on
30 the implementation of the C library if the capacity is exceeded. If the capacity
31 needs to be extended, the memory is reallocated. The mentioned complexity rules
32 only apply as long as (cap > siz + 1). *Usually*, realloc will have a complexity
33 of either O(1), if the memory block happens to be already big enough, or
34 O(n) + X, if a new, bigger block needs to be allocated and the memory copied.
36 Note that when the capacity is extended, it is possible to allocated more space space
37 than needed, to prevent frequent calls to append/insert from having to reallocate
38 the memory every time. If, and if yes how much additional space is allocated is
39 determined by the extra space field. Extra space for ext elements is allocated
40 whenever a growth reallocation happens.
42 The array can be sorted. In this case, the array is expected to have a comparator cmp
45 The comparison function must return an integer less than, equal to, or greater than
46 zero if the first argument is considered to be respectively less than, equal to,
47 or greater than the second. If two members compare as equal, their order in the
48 sorted array is undefined. [Copied from the Linux man-pages]
50 The sorting function uses the quicksort algorithm from the C library, which has an
51 average complexity of O(n log n).
53 To maintain the order of a sorted array, add and put should not be used.
56 #ifndef _DRAGONSTD_ARRAY_H_ // include guard
57 #define _DRAGONSTD_ARRAY_H_
59 #include <stddef.h> // for size_t
60 #include <sys/types.h> // for ssize_t
62 typedef int (*ArrayComparator)(const void *va, const void *vb);
67 size_t ext; // extra space
68 ArrayComparator cmp; // comparator
70 size_t mbs; // member size
71 size_t siz; // used space
72 size_t cap; // available space
75 void array_ini(Array *array, size_t mmb, size_t ext, ArrayComparator cmp);
77 Initializes the array.
79 The array will have the member size of mmb and the extra space set to ext.
80 mmb should be bigger than 0 and may not be changed after the initialization.
81 ext can be 0 or bigger and may be changed any time.
82 The comparator of the array is set to cmp and may be nil.
84 This function should be called before calling any other functions on the
87 This function should not be called on an array that has been initialized before,
88 unless the array either has a capacity of 0 or it has been deleted using
89 array_del. Otherwise a memory leak will occur.
92 void array_rlc(Array *array);
94 Reallocates the array's memory to match it's capacity.
96 This function should be called every time the capacity has changed.
99 void array_grw(Array *array, size_t n);
101 Grows the array by n bytes.
103 This function increases the arrays size by n bytes. If this exceeds the capacity of
104 the array, the capacity set to the size and the extra space ext is added to it.
106 If the capacity is changed, the array is reallocated.
108 If n is zero, the array's capacity may still grow by extra space if it exactly
109 matches the current size.
112 void array_shr(Array *array, size_t n);
114 Shrinks the array by n bytes.
116 This function decreases the arrays size by n bytes.
118 If the array has additional capacity left after it has been shrunk, the capacity
119 is set to the new size and the array is reallocated to fit the new capacity.
120 For n > 0, this is always the case, for n = 0, this may be the case.
122 Note that calling this function with n = 0 is useful to shrink the array's memory to
123 exactly fit it's used size.
126 void array_put(Array *array, const void *ptr, size_t n);
128 Grows the array by 1 and inserts ptr at the index n.
130 This function inserts the memory pointed to by ptr before the array member at
131 index n, moving all elements from that index to the end of the array.
133 After this operation, the inserted element will be _at_ the index n.
135 The memory that ptr points to, which's size is assumed to be at least as big as the
136 array's member size is copied into the arrays memory.
138 n should be in the range from 0 to the array's size.
141 void array_add(Array *array, const void *ptr);
143 Grows the array by 1 and appends ptr at the end of the array.
145 This function's result is equivalent to calling array_put(array, ptr, array->siz),
146 but it is slightly faster since it saves unnecessary calls.
149 void array_cpy(Array *array, void **ptr, size_t *n);
151 Allocates a buffer big enough to fit the array's used size.
152 Copies the array's contents into the allocated buffer.
153 Returns the buffer in ptr and the size in n.
155 Note that the returned size is the number of elements, not the number of bytes.
158 void array_cln(Array *dst, Array *src);
160 Clones the array src to the array dst.
162 dst is initialized to have the same configuration (member size, extra space,
165 After the operation, the contents of the array dst are be the same as those of src.
166 The size of dst and src are the same, the capacity of dst however is the same as
167 the size of dst and src (which might not equal the capacity of src).
169 Since array_ini is called on dst, it should be uninitialized, empty or deleted.
172 void array_rcy(Array *array);
176 This function sets the used size of the array to 0 but leaves the capacity unchanged.
177 The array's memory is not free'd and the array can be reused.
180 void array_del(Array *array);
184 This function frees the arrays memory. If this is not called when the array's
185 reference is dropped, a memory leak occurs, unless the array is empty (capacity
186 of 0), in which case the function does not need to be called. The function works
187 fine on empty arrays however.
189 After this, the array should no longer be used until reinitialized.
192 void array_srt(Array *array);
194 Sorts the array using the quicksort algorithm.
196 The array is assumed to have a non-NULL comparator.
197 Wraps the qsort C-library routine. Please refer to it's documentation.
200 ssize_t array_fnd(Array *array, const void *ptr, size_t *idx);
202 Searches the sorted array for the element ptr.
203 Returns the index of the element, or -1 if it wasn't found.
205 If idx is not NULL, a pointer to the last searched index is saved to where it
206 points to. This is the index ptr would need to be inserted at to keep the order.
208 It is assumed that the array has been sorted by array_srt before (or was empty),
209 and the order has been kept and the comparator has not been changed since.
212 size_t array_ins(Array *array, const void *ptr);
214 Inserts an element into a sorted array, keeping the order.
215 Returns the index the element has been inserted at.
217 Calls array_fnd and array_put.
219 It is assumed that the array has been sorted by array_srt before (or was empty),
220 and the order has been kept and the comparator has not been changed since.
223 #endif // _DRAGONSTD_ARRAY_H_