Merge branch 'jc/mkstemp-more-careful-error-reporting'
[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 `sort_string_list`.
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 `filter_string_list`::
72
73 Apply a function to each item in a list, retaining only the
74 items for which the function returns true. If free_util is
75 true, call free() on the util members of any items that have
76 to be deleted. Preserve the order of the items that are
77 retained.
78
79 `string_list_remove_empty_items`::
80
81 Remove any empty strings from the list. If free_util is true,
82 call free() on the util members of any items that have to be
83 deleted. Preserve the order of the items that are retained.
84
85 `print_string_list`::
86
87 Dump a string_list to stdout, useful mainly for debugging purposes. It
88 can take an optional header argument and it writes out the
89 string-pointer pairs of the string_list, each one in its own line.
90
91 `string_list_clear`::
92
93 Free a string_list. The `string` pointer of the items will be freed in
94 case the `strdup_strings` member of the string_list is set. The second
95 parameter controls if the `util` pointer of the items should be freed
96 or not.
97
98 * Functions for sorted lists only
99
100 `string_list_has_string`::
101
102 Determine if the string_list has a given string or not.
103
104 `string_list_insert`::
105
106 Insert a new element to the string_list. The returned pointer can be
107 handy if you want to write something to the `util` pointer of the
108 string_list_item containing the just added string. If the given
109 string already exists the insertion will be skipped and the
110 pointer to the existing item returned.
111 +
112 Since this function uses xrealloc() (which die()s if it fails) if the
113 list needs to grow, it is safe not to check the pointer. I.e. you may
114 write `string_list_insert(...)->util = ...;`.
115
116 `string_list_lookup`::
117
118 Look up a given string in the string_list, returning the containing
119 string_list_item. If the string is not found, NULL is returned.
120
121 `string_list_remove_duplicates`::
122
123 Remove all but the first of consecutive entries that have the
124 same string value. If free_util is true, call free() on the
125 util members of any items that have to be deleted.
126
127 * Functions for unsorted lists only
128
129 `string_list_append`::
130
131 Append a new string to the end of the string_list. If
132 `strdup_string` is set, then the string argument is copied;
133 otherwise the new `string_list_entry` refers to the input
134 string.
135
136 `string_list_append_nodup`::
137
138 Append a new string to the end of the string_list. The new
139 `string_list_entry` always refers to the input string, even if
140 `strdup_string` is set. This function can be used to hand
141 ownership of a malloc()ed string to a `string_list` that has
142 `strdup_string` set.
143
144 `sort_string_list`::
145
146 Sort the list's entries by string value in `strcmp()` order.
147
148 `unsorted_string_list_has_string`::
149
150 It's like `string_list_has_string()` but for unsorted lists.
151
152 `unsorted_string_list_lookup`::
153
154 It's like `string_list_lookup()` but for unsorted lists.
155 +
156 The above two functions need to look through all items, as opposed to their
157 counterpart for sorted lists, which performs a binary search.
158
159 `unsorted_string_list_delete_item`::
160
161 Remove an item from a string_list. The `string` pointer of the items
162 will be freed in case the `strdup_strings` member of the string_list
163 is set. The third parameter controls if the `util` pointer of the
164 items should be freed or not.
165
166 `string_list_split`::
167 `string_list_split_in_place`::
168
169 Split a string into substrings on a delimiter character and
170 append the substrings to a `string_list`. If `maxsplit` is
171 non-negative, then split at most `maxsplit` times. Return the
172 number of substrings appended to the list.
173 +
174 `string_list_split` requires a `string_list` that has `strdup_strings`
175 set to true; it leaves the input string untouched and makes copies of
176 the substrings in newly-allocated memory.
177 `string_list_split_in_place` requires a `string_list` that has
178 `strdup_strings` set to false; it splits the input string in place,
179 overwriting the delimiter characters with NULs and creating new
180 string_list_items that point into the original string (the original
181 string must therefore not be modified or freed while the `string_list`
182 is in use).
183
184
185 Data structures
186 ---------------
187
188 * `struct string_list_item`
189
190 Represents an item of the list. The `string` member is a pointer to the
191 string, and you may use the `util` member for any purpose, if you want.
192
193 * `struct string_list`
194
195 Represents the list itself.
196
197 . The array of items are available via the `items` member.
198 . The `nr` member contains the number of items stored in the list.
199 . The `alloc` member is used to avoid reallocating at every insertion.
200 You should not tamper with it.
201 . Setting the `strdup_strings` member to 1 will strdup() the strings
202 before adding them, see above.