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ef416fc2 | 1 | <!-- |
eac3a0a0 | 2 | Array API introduction for CUPS. |
ef416fc2 | 3 | |
eac3a0a0 | 4 | Copyright 2007-2011 by Apple Inc. |
bc44d920 | 5 | Copyright 1997-2006 by Easy Software Products, all rights reserved. |
ef416fc2 | 6 | |
7 | These coded instructions, statements, and computer programs are the | |
bc44d920 | 8 | property of Apple Inc. and are protected by Federal copyright |
9 | law. Distribution and use rights are outlined in the file "LICENSE.txt" | |
10 | which should have been included with this file. If this file is | |
11 | file is missing or damaged, see the license at "http://www.cups.org/". | |
ef416fc2 | 12 | --> |
13 | ||
5a738aea | 14 | <h2 class='title'><a name='OVERVIEW'>Overview</a></h2> |
ef416fc2 | 15 | |
5a738aea MS |
16 | <p>The CUPS array API provides a high-performance generic array container. |
17 | The contents of the array container can be sorted and the container itself is | |
18 | designed for optimal speed and memory usage under a wide variety of conditions. | |
19 | Sorted arrays use a binary search algorithm from the last found or inserted | |
20 | element to quickly find matching elements in the array. Arrays created with the | |
21 | optional hash function can often find elements with a single lookup. The | |
22 | <a href='#cups_array_t'><code>cups_array_t</code></a> type is used when | |
23 | referring to a CUPS array.</p> | |
ef416fc2 | 24 | |
25 | <p>The CUPS scheduler (<tt>cupsd</tt>) and many of the CUPS API | |
26 | functions use the array API to efficiently manage large lists of | |
27 | data.</p> | |
28 | ||
5a738aea | 29 | <h3><a name='MANAGING_ARRAYS'>Managing Arrays</a></h3> |
ef416fc2 | 30 | |
5a738aea | 31 | <p>Arrays are created using either the |
10d09e33 MS |
32 | <a href='#cupsArrayNew'><code>cupsArrayNew</code></a>, |
33 | <a href='#cupsArrayNew2'><code>cupsArrayNew2</code></a>, or | |
34 | <a href='#cupsArrayNew2'><code>cupsArrayNew3</code></a> functions. The | |
5a738aea MS |
35 | first function creates a new array with the specified callback function |
36 | and user data pointer:</p> | |
ef416fc2 | 37 | |
5a738aea MS |
38 | <pre class='example'> |
39 | #include <cups/array.h> | |
ef416fc2 | 40 | |
5a738aea MS |
41 | static int compare_func(void *first, void *second, void *user_data); |
42 | ||
43 | void *user_data; | |
44 | <a href='#cups_array_t'>cups_array_t</a> *array = <a href='#cupsArrayNew'>cupsArrayNew</a>(compare_func, user_data); | |
45 | </pre> | |
46 | ||
47 | <p>The comparison function (type | |
48 | <a href="#cups_arrayfunc_t"><code>cups_arrayfunc_t</code></a>) is called | |
49 | whenever an element is added to the array and can be <code>NULL</code> to | |
50 | create an unsorted array. The function returns -1 if the first element should | |
51 | come before the second, 0 if the first and second elements should have the same | |
52 | ordering, and 1 if the first element should come after the second.</p> | |
53 | ||
54 | <p>The "user_data" pointer is passed to your comparison function. Pass | |
55 | <code>NULL</code> if you do not need to associate the elements in your array | |
56 | with additional information.</p> | |
57 | ||
58 | <p>The <a href='#cupsArrayNew2'><code>cupsArrayNew2</code></a> function adds | |
59 | two more arguments to support hashed lookups, which can potentially provide | |
60 | instantaneous ("O(1)") lookups in your array:</p> | |
61 | ||
62 | <pre class='example'> | |
63 | #include <cups/array.h> | |
64 | ||
65 | #define HASH_SIZE 512 /* Size of hash table */ | |
66 | ||
67 | static int compare_func(void *first, void *second, void *user_data); | |
68 | static int hash_func(void *element, void *user_data); | |
69 | ||
70 | void *user_data; | |
10d09e33 | 71 | <a href='#cups_array_t'>cups_array_t</a> *hash_array = <a href='#cupsArrayNew2'>cupsArrayNew2</a>(compare_func, user_data, hash_func, HASH_SIZE); |
5a738aea MS |
72 | </pre> |
73 | ||
74 | <p>The hash function (type | |
79e1d494 | 75 | <a href="#cups_ahash_func_t"><code>cups_ahash_func_t</code></a>) should return a |
5a738aea MS |
76 | number from 0 to (hash_size-1) that (hopefully) uniquely identifies the |
77 | element and is called whenever you look up an element in the array with | |
78 | <a href='#cupsArrayFind'><code>cupsArrayFind</code></a>. The hash size is | |
79 | only limited by available memory, but generally should not be larger than | |
80 | 16384 to realize any performance improvement.</p> | |
81 | ||
10d09e33 MS |
82 | <p>The <a href='#cupsArrayNew3'><code>cupsArrayNew3</code></a> function adds |
83 | copy and free callbacks to support basic memory management of elements:</p> | |
84 | ||
85 | <pre class='example'> | |
86 | #include <cups/array.h> | |
87 | ||
88 | #define HASH_SIZE 512 /* Size of hash table */ | |
89 | ||
90 | static int compare_func(void *first, void *second, void *user_data); | |
91 | static void *copy_func(void *element, void *user_data); | |
92 | static void free_func(void *element, void *user_data); | |
93 | static int hash_func(void *element, void *user_data); | |
94 | ||
95 | void *user_data; | |
96 | <a href='#cups_array_t'>cups_array_t</a> *array = <a href='#cupsArrayNew3'>cupsArrayNew3</a>(compare_func, user_data, NULL, 0, copy_func, free_func); | |
97 | ||
98 | <a href='#cups_array_t'>cups_array_t</a> *hash_array = <a href='#cupsArrayNew3'>cupsArrayNew3</a>(compare_func, user_data, hash_func, HASH_SIZE, copy_func, free_func); | |
99 | </pre> | |
100 | ||
5a738aea MS |
101 | <p>Once you have created the array, you add elements using the |
102 | <a href='#cupsArrayAdd'><code>cupsArrayAdd</code></a> | |
103 | <a href='#cupsArrayInsert'><code>cupsArrayInsert</code></a> functions. | |
104 | The first function adds an element to the array, adding the new element | |
105 | after any elements that have the same order, while the second inserts the | |
106 | element before others with the same order. For unsorted arrays, | |
79e1d494 | 107 | <a href='#cupsArrayAdd'><code>cupsArrayAdd</code></a> appends the element to |
5a738aea MS |
108 | the end of the array while |
109 | <a href='#cupsArrayInsert'><code>cupsArrayInsert</code></a> inserts the | |
110 | element at the beginning of the array. For example, the following code | |
111 | creates a sorted array of character strings:</p> | |
112 | ||
113 | <pre class='example'> | |
114 | #include <cups/array.h> | |
115 | ||
116 | /* Use strcmp() to compare strings - it will ignore the user_data pointer */ | |
117 | <a href='#cups_array_t'>cups_array_t</a> *array = <a href='#cupsArrayNew'>cupsArrayNew</a>((<a href='#cups_array_func_t'>cups_array_func_t</a>)strcmp, NULL); | |
118 | ||
119 | /* Add four strings to the array */ | |
120 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "One Fish"); | |
121 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Two Fish"); | |
122 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Red Fish"); | |
123 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Blue Fish"); | |
ef416fc2 | 124 | </pre> |
125 | ||
5a738aea MS |
126 | <p>Elements are removed using the |
127 | <a href='#cupsArrayRemove'><code>cupsArrayRemove</code></a> function, for | |
128 | example:</p> | |
ef416fc2 | 129 | |
5a738aea MS |
130 | <pre class='example'> |
131 | #include <cups/array.h> | |
132 | ||
133 | /* Use strcmp() to compare strings - it will ignore the user_data pointer */ | |
134 | <a href='#cups_array_t'>cups_array_t</a> *array = <a href='#cupsArrayNew'>cupsArrayNew</a>((<a href='#cups_array_func_t'>cups_array_func_t</a>)strcmp, NULL); | |
135 | ||
136 | /* Add four strings to the array */ | |
137 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "One Fish"); | |
138 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Two Fish"); | |
139 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Red Fish"); | |
140 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Blue Fish"); | |
141 | ||
142 | /* Remove "Red Fish" */ | |
143 | <a href='#cupsArrayRemove'>cupsArrayRemove</a>(array, "Red Fish"); | |
144 | </pre> | |
145 | ||
146 | <p>Finally, you free the memory used by the array using the | |
147 | <a href='#cupsArrayDelete'><code>cupsArrayDelete</code></a> function. All | |
148 | of the memory for the array and hash table (if any) is freed, however <em>CUPS | |
10d09e33 | 149 | does not free the elements unless you provide copy and free functions</em>.</p> |
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150 | |
151 | <h3><a name='FINDING_AND_ENUMERATING'>Finding and Enumerating Elements</a></h3> | |
152 | ||
153 | <p>CUPS provides several functions to find and enumerate elements in an | |
154 | array. Each one sets or updates a "current index" into the array, such that | |
155 | future lookups will start where the last one left off:</p> | |
156 | ||
157 | <dl> | |
158 | <dt><a href='#cupsArrayFind'><code>cupsArrayFind</code></a></dt> | |
79e1d494 | 159 | <dd>Returns the first matching element.</dd> |
5a738aea MS |
160 | <dt><a href='#cupsArrayFirst'><code>cupsArrayFirst</code></a></dt> |
161 | <dd>Returns the first element in the array.</dd> | |
162 | <dt><a href='#cupsArrayIndex'><code>cupsArrayIndex</code></a></dt> | |
79e1d494 | 163 | <dd>Returns the Nth element in the array, starting at 0.</dd> |
5a738aea MS |
164 | <dt><a href='#cupsArrayLast'><code>cupsArrayLast</code></a></dt> |
165 | <dd>Returns the last element in the array.</dd> | |
166 | <dt><a href='#cupsArrayNext'><code>cupsArrayNext</code></a></dt> | |
167 | <dd>Returns the next element in the array.</dd> | |
168 | <dt><a href='#cupsArrayPrev'><code>cupsArrayPrev</code></a></dt> | |
169 | <dd>Returns the previous element in the array.</dd> | |
170 | </dl> | |
171 | ||
172 | <p>Each of these functions returns <code>NULL</code> when there is no | |
173 | corresponding element. For example, a simple <code>for</code> loop using the | |
174 | <a href='#cupsArrayFirst'><code>cupsArrayFirst</code></a> and | |
175 | <a href='#cupsArrayNext'><code>cupsArrayNext</code></a> functions will | |
176 | enumerate all of the strings in our previous example:</p> | |
177 | ||
178 | <pre class='example'> | |
179 | #include <cups/array.h> | |
180 | ||
181 | /* Use strcmp() to compare strings - it will ignore the user_data pointer */ | |
182 | <a href='#cups_array_t'>cups_array_t</a> *array = <a href='#cupsArrayNew'>cupsArrayNew</a>((<a href='#cups_array_func_t'>cups_array_func_t</a>)strcmp, NULL); | |
183 | ||
184 | /* Add four strings to the array */ | |
185 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "One Fish"); | |
186 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Two Fish"); | |
187 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Red Fish"); | |
188 | <a href='#cupsArrayAdd'>cupsArrayAdd</a>(array, "Blue Fish"); | |
189 | ||
190 | /* Show all of the strings in the array */ | |
191 | char *s; | |
192 | for (s = (char *)<a href='#cupsArrayFirst'>cupsArrayFirst</a>(array); s != NULL; s = (char *)<a href='#cupsArrayNext'>cupsArrayNext</a>(array)) | |
193 | puts(s); | |
194 | </pre> |