sort_string_list(): rename to string_list_sort()
[git/git.git] / Documentation / technical / api-string-list.txt
1 string-list API
2 ===============
3
4 The string_list API offers a data structure and functions to handle
5 sorted and unsorted string lists. A "sorted" list is one whose
6 entries are sorted by string value in `strcmp()` order.
7
8 The 'string_list' struct used to be called 'path_list', but was renamed
9 because it is not specific to paths.
10
11 The caller:
12
13 . Allocates and clears a `struct string_list` variable.
14
15 . Initializes the members. You might want to set the flag `strdup_strings`
16 if the strings should be strdup()ed. For example, this is necessary
17 when you add something like git_path("..."), since that function returns
18 a static buffer that will change with the next call to git_path().
19 +
20 If you need something advanced, you can manually malloc() the `items`
21 member (you need this if you add things later) and you should set the
22 `nr` and `alloc` members in that case, too.
23
24 . Adds new items to the list, using `string_list_append`,
25 `string_list_append_nodup`, `string_list_insert`,
26 `string_list_split`, and/or `string_list_split_in_place`.
27
28 . Can check if a string is in the list using `string_list_has_string` or
29 `unsorted_string_list_has_string` and get it from the list using
30 `string_list_lookup` for sorted lists.
31
32 . Can sort an unsorted list using `string_list_sort`.
33
34 . Can remove duplicate items from a sorted list using
35 `string_list_remove_duplicates`.
36
37 . Can remove individual items of an unsorted list using
38 `unsorted_string_list_delete_item`.
39
40 . Can remove items not matching a criterion from a sorted or unsorted
41 list using `filter_string_list`, or remove empty strings using
42 `string_list_remove_empty_items`.
43
44 . Finally it should free the list using `string_list_clear`.
45
46 Example:
47
48 ----
49 struct string_list list = STRING_LIST_INIT_NODUP;
50 int i;
51
52 string_list_append(&list, "foo");
53 string_list_append(&list, "bar");
54 for (i = 0; i < list.nr; i++)
55 printf("%s\n", list.items[i].string)
56 ----
57
58 NOTE: It is more efficient to build an unsorted list and sort it
59 afterwards, instead of building a sorted list (`O(n log n)` instead of
60 `O(n^2)`).
61 +
62 However, if you use the list to check if a certain string was added
63 already, you should not do that (using unsorted_string_list_has_string()),
64 because the complexity would be quadratic again (but with a worse factor).
65
66 Functions
67 ---------
68
69 * General ones (works with sorted and unsorted lists as well)
70
71 `string_list_init`::
72
73 Initialize the members of the string_list, set `strdup_strings`
74 member according to the value of the second parameter.
75
76 `filter_string_list`::
77
78 Apply a function to each item in a list, retaining only the
79 items for which the function returns true. If free_util is
80 true, call free() on the util members of any items that have
81 to be deleted. Preserve the order of the items that are
82 retained.
83
84 `string_list_remove_empty_items`::
85
86 Remove any empty strings from the list. If free_util is true,
87 call free() on the util members of any items that have to be
88 deleted. Preserve the order of the items that are retained.
89
90 `print_string_list`::
91
92 Dump a string_list to stdout, useful mainly for debugging purposes. It
93 can take an optional header argument and it writes out the
94 string-pointer pairs of the string_list, each one in its own line.
95
96 `string_list_clear`::
97
98 Free a string_list. The `string` pointer of the items will be freed in
99 case the `strdup_strings` member of the string_list is set. The second
100 parameter controls if the `util` pointer of the items should be freed
101 or not.
102
103 * Functions for sorted lists only
104
105 `string_list_has_string`::
106
107 Determine if the string_list has a given string or not.
108
109 `string_list_insert`::
110
111 Insert a new element to the string_list. The returned pointer can be
112 handy if you want to write something to the `util` pointer of the
113 string_list_item containing the just added string. If the given
114 string already exists the insertion will be skipped and the
115 pointer to the existing item returned.
116 +
117 Since this function uses xrealloc() (which die()s if it fails) if the
118 list needs to grow, it is safe not to check the pointer. I.e. you may
119 write `string_list_insert(...)->util = ...;`.
120
121 `string_list_lookup`::
122
123 Look up a given string in the string_list, returning the containing
124 string_list_item. If the string is not found, NULL is returned.
125
126 `string_list_remove_duplicates`::
127
128 Remove all but the first of consecutive entries that have the
129 same string value. If free_util is true, call free() on the
130 util members of any items that have to be deleted.
131
132 * Functions for unsorted lists only
133
134 `string_list_append`::
135
136 Append a new string to the end of the string_list. If
137 `strdup_string` is set, then the string argument is copied;
138 otherwise the new `string_list_entry` refers to the input
139 string.
140
141 `string_list_append_nodup`::
142
143 Append a new string to the end of the string_list. The new
144 `string_list_entry` always refers to the input string, even if
145 `strdup_string` is set. This function can be used to hand
146 ownership of a malloc()ed string to a `string_list` that has
147 `strdup_string` set.
148
149 `string_list_sort`::
150
151 Sort the list's entries by string value in `strcmp()` order.
152
153 `unsorted_string_list_has_string`::
154
155 It's like `string_list_has_string()` but for unsorted lists.
156
157 `unsorted_string_list_lookup`::
158
159 It's like `string_list_lookup()` but for unsorted lists.
160 +
161 The above two functions need to look through all items, as opposed to their
162 counterpart for sorted lists, which performs a binary search.
163
164 `unsorted_string_list_delete_item`::
165
166 Remove an item from a string_list. The `string` pointer of the items
167 will be freed in case the `strdup_strings` member of the string_list
168 is set. The third parameter controls if the `util` pointer of the
169 items should be freed or not.
170
171 `string_list_split`::
172 `string_list_split_in_place`::
173
174 Split a string into substrings on a delimiter character and
175 append the substrings to a `string_list`. If `maxsplit` is
176 non-negative, then split at most `maxsplit` times. Return the
177 number of substrings appended to the list.
178 +
179 `string_list_split` requires a `string_list` that has `strdup_strings`
180 set to true; it leaves the input string untouched and makes copies of
181 the substrings in newly-allocated memory.
182 `string_list_split_in_place` requires a `string_list` that has
183 `strdup_strings` set to false; it splits the input string in place,
184 overwriting the delimiter characters with NULs and creating new
185 string_list_items that point into the original string (the original
186 string must therefore not be modified or freed while the `string_list`
187 is in use).
188
189
190 Data structures
191 ---------------
192
193 * `struct string_list_item`
194
195 Represents an item of the list. The `string` member is a pointer to the
196 string, and you may use the `util` member for any purpose, if you want.
197
198 * `struct string_list`
199
200 Represents the list itself.
201
202 . The array of items are available via the `items` member.
203 . The `nr` member contains the number of items stored in the list.
204 . The `alloc` member is used to avoid reallocating at every insertion.
205 You should not tamper with it.
206 . Setting the `strdup_strings` member to 1 will strdup() the strings
207 before adding them, see above.
208 . The `compare_strings_fn` member is used to specify a custom compare
209 function, otherwise `strcmp()` is used as the default function.