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[git/git.git] / Documentation / technical / api-string-list.txt
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1string-list API
2===============
3
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4The string_list API offers a data structure and functions to handle
5sorted and unsorted string lists. A "sorted" list is one whose
6entries are sorted by string value in `strcmp()` order.
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7
8The 'string_list' struct used to be called 'path_list', but was renamed
9because it is not specific to paths.
10
11The 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+
20If you need something advanced, you can manually malloc() the `items`
21member (you need this if you add things later) and you should set the
22`nr` and `alloc` members in that case, too.
23
e448fed8 24. Adds new items to the list, using `string_list_append`,
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25 `string_list_append_nodup`, `string_list_insert`,
26 `string_list_split`, and/or `string_list_split_in_place`.
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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
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34. Can remove duplicate items from a sorted list using
35 `string_list_remove_duplicates`.
36
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37. Can remove individual items of an unsorted list using
38 `unsorted_string_list_delete_item`.
39
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40. Can remove items not matching a criterion from a sorted or unsorted
41 list using `filter_string_list`.
42
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43. Finally it should free the list using `string_list_clear`.
44
45Example:
46
47----
51f3145c 48struct string_list list = STRING_LIST_INIT_NODUP;
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49int i;
50
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51string_list_append(&list, "foo");
52string_list_append(&list, "bar");
c455c87c 53for (i = 0; i < list.nr; i++)
0dda1d1e 54 printf("%s\n", list.items[i].string)
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55----
56
57NOTE: It is more efficient to build an unsorted list and sort it
58afterwards, instead of building a sorted list (`O(n log n)` instead of
59`O(n^2)`).
60+
61However, if you use the list to check if a certain string was added
62already, you should not do that (using unsorted_string_list_has_string()),
63because the complexity would be quadratic again (but with a worse factor).
64
65Functions
66---------
67
68* General ones (works with sorted and unsorted lists as well)
69
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70`filter_string_list`::
71
72 Apply a function to each item in a list, retaining only the
73 items for which the function returns true. If free_util is
74 true, call free() on the util members of any items that have
75 to be deleted. Preserve the order of the items that are
76 retained.
77
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78`string_list_longest_prefix`::
79
80 Return the longest string within a string_list that is a
81 prefix (in the sense of prefixcmp()) of the specified string,
82 or NULL if no such prefix exists. This function does not
83 require the string_list to be sorted (it does a linear
84 search).
85
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86`print_string_list`::
87
88 Dump a string_list to stdout, useful mainly for debugging purposes. It
89 can take an optional header argument and it writes out the
90 string-pointer pairs of the string_list, each one in its own line.
91
92`string_list_clear`::
93
94 Free a string_list. The `string` pointer of the items will be freed in
95 case the `strdup_strings` member of the string_list is set. The second
96 parameter controls if the `util` pointer of the items should be freed
97 or not.
98
99* Functions for sorted lists only
100
101`string_list_has_string`::
102
103 Determine if the string_list has a given string or not.
104
105`string_list_insert`::
106
107 Insert a new element to the string_list. The returned pointer can be
108 handy if you want to write something to the `util` pointer of the
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109 string_list_item containing the just added string. If the given
110 string already exists the insertion will be skipped and the
111 pointer to the existing item returned.
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112+
113Since this function uses xrealloc() (which die()s if it fails) if the
114list needs to grow, it is safe not to check the pointer. I.e. you may
115write `string_list_insert(...)->util = ...;`.
116
117`string_list_lookup`::
118
119 Look up a given string in the string_list, returning the containing
120 string_list_item. If the string is not found, NULL is returned.
121
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122`string_list_remove_duplicates`::
123
124 Remove all but the first of consecutive entries that have the
125 same string value. If free_util is true, call free() on the
126 util members of any items that have to be deleted.
127
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128* Functions for unsorted lists only
129
130`string_list_append`::
131
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132 Append a new string to the end of the string_list. If
133 `strdup_string` is set, then the string argument is copied;
134 otherwise the new `string_list_entry` refers to the input
135 string.
136
137`string_list_append_nodup`::
138
139 Append a new string to the end of the string_list. The new
140 `string_list_entry` always refers to the input string, even if
141 `strdup_string` is set. This function can be used to hand
142 ownership of a malloc()ed string to a `string_list` that has
143 `strdup_string` set.
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144
145`sort_string_list`::
146
1959bf64 147 Sort the list's entries by string value in `strcmp()` order.
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148
149`unsorted_string_list_has_string`::
150
151 It's like `string_list_has_string()` but for unsorted lists.
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152
153`unsorted_string_list_lookup`::
154
155 It's like `string_list_lookup()` but for unsorted lists.
c455c87c 156+
e2421480 157The above two functions need to look through all items, as opposed to their
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158counterpart for sorted lists, which performs a binary search.
159
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160`unsorted_string_list_delete_item`::
161
162 Remove an item from a string_list. The `string` pointer of the items
163 will be freed in case the `strdup_strings` member of the string_list
164 is set. The third parameter controls if the `util` pointer of the
165 items should be freed or not.
166
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167`string_list_split`::
168`string_list_split_in_place`::
169
170 Split a string into substrings on a delimiter character and
171 append the substrings to a `string_list`. If `maxsplit` is
172 non-negative, then split at most `maxsplit` times. Return the
173 number of substrings appended to the list.
174+
175`string_list_split` requires a `string_list` that has `strdup_strings`
176set to true; it leaves the input string untouched and makes copies of
177the substrings in newly-allocated memory.
178`string_list_split_in_place` requires a `string_list` that has
179`strdup_strings` set to false; it splits the input string in place,
180overwriting the delimiter characters with NULs and creating new
181string_list_items that point into the original string (the original
182string must therefore not be modified or freed while the `string_list`
183is in use).
184
185
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186Data structures
187---------------
188
189* `struct string_list_item`
190
0dda1d1e 191Represents an item of the list. The `string` member is a pointer to the
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192string, and you may use the `util` member for any purpose, if you want.
193
194* `struct string_list`
195
196Represents the list itself.
197
198. The array of items are available via the `items` member.
199. The `nr` member contains the number of items stored in the list.
200. The `alloc` member is used to avoid reallocating at every insertion.
201 You should not tamper with it.
202. Setting the `strdup_strings` member to 1 will strdup() the strings
203 before adding them, see above.