string_list: add a new function, string_list_remove_duplicates()
[git/git.git] / Documentation / technical / api-string-list.txt
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1string-list API
2===============
3
4The string_list API offers a data structure and functions to handle sorted
5and unsorted string lists.
6
7The 'string_list' struct used to be called 'path_list', but was renamed
8because it is not specific to paths.
9
10The caller:
11
12. Allocates and clears a `struct string_list` variable.
13
14. Initializes the members. You might want to set the flag `strdup_strings`
15 if the strings should be strdup()ed. For example, this is necessary
16 when you add something like git_path("..."), since that function returns
17 a static buffer that will change with the next call to git_path().
18+
19If you need something advanced, you can manually malloc() the `items`
20member (you need this if you add things later) and you should set the
21`nr` and `alloc` members in that case, too.
22
e448fed8 23. Adds new items to the list, using `string_list_append`,
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24 `string_list_append_nodup`, `string_list_insert`,
25 `string_list_split`, and/or `string_list_split_in_place`.
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26
27. Can check if a string is in the list using `string_list_has_string` or
28 `unsorted_string_list_has_string` and get it from the list using
29 `string_list_lookup` for sorted lists.
30
31. Can sort an unsorted list using `sort_string_list`.
32
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33. Can remove duplicate items from a sorted list using
34 `string_list_remove_duplicates`.
35
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36. Can remove individual items of an unsorted list using
37 `unsorted_string_list_delete_item`.
38
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39. Can remove items not matching a criterion from a sorted or unsorted
40 list using `filter_string_list`.
41
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42. Finally it should free the list using `string_list_clear`.
43
44Example:
45
46----
47struct string_list list;
48int i;
49
50memset(&list, 0, sizeof(struct string_list));
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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`print_string_list`::
79
80 Dump a string_list to stdout, useful mainly for debugging purposes. It
81 can take an optional header argument and it writes out the
82 string-pointer pairs of the string_list, each one in its own line.
83
84`string_list_clear`::
85
86 Free a string_list. The `string` pointer of the items will be freed in
87 case the `strdup_strings` member of the string_list is set. The second
88 parameter controls if the `util` pointer of the items should be freed
89 or not.
90
91* Functions for sorted lists only
92
93`string_list_has_string`::
94
95 Determine if the string_list has a given string or not.
96
97`string_list_insert`::
98
99 Insert a new element to the string_list. The returned pointer can be
100 handy if you want to write something to the `util` pointer of the
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101 string_list_item containing the just added string. If the given
102 string already exists the insertion will be skipped and the
103 pointer to the existing item returned.
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104+
105Since this function uses xrealloc() (which die()s if it fails) if the
106list needs to grow, it is safe not to check the pointer. I.e. you may
107write `string_list_insert(...)->util = ...;`.
108
109`string_list_lookup`::
110
111 Look up a given string in the string_list, returning the containing
112 string_list_item. If the string is not found, NULL is returned.
113
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114`string_list_remove_duplicates`::
115
116 Remove all but the first of consecutive entries that have the
117 same string value. If free_util is true, call free() on the
118 util members of any items that have to be deleted.
119
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120* Functions for unsorted lists only
121
122`string_list_append`::
123
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124 Append a new string to the end of the string_list. If
125 `strdup_string` is set, then the string argument is copied;
126 otherwise the new `string_list_entry` refers to the input
127 string.
128
129`string_list_append_nodup`::
130
131 Append a new string to the end of the string_list. The new
132 `string_list_entry` always refers to the input string, even if
133 `strdup_string` is set. This function can be used to hand
134 ownership of a malloc()ed string to a `string_list` that has
135 `strdup_string` set.
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136
137`sort_string_list`::
138
139 Make an unsorted list sorted.
140
141`unsorted_string_list_has_string`::
142
143 It's like `string_list_has_string()` but for unsorted lists.
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144
145`unsorted_string_list_lookup`::
146
147 It's like `string_list_lookup()` but for unsorted lists.
c455c87c 148+
e2421480 149The above two functions need to look through all items, as opposed to their
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150counterpart for sorted lists, which performs a binary search.
151
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152`unsorted_string_list_delete_item`::
153
154 Remove an item from a string_list. The `string` pointer of the items
155 will be freed in case the `strdup_strings` member of the string_list
156 is set. The third parameter controls if the `util` pointer of the
157 items should be freed or not.
158
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159`string_list_split`::
160`string_list_split_in_place`::
161
162 Split a string into substrings on a delimiter character and
163 append the substrings to a `string_list`. If `maxsplit` is
164 non-negative, then split at most `maxsplit` times. Return the
165 number of substrings appended to the list.
166+
167`string_list_split` requires a `string_list` that has `strdup_strings`
168set to true; it leaves the input string untouched and makes copies of
169the substrings in newly-allocated memory.
170`string_list_split_in_place` requires a `string_list` that has
171`strdup_strings` set to false; it splits the input string in place,
172overwriting the delimiter characters with NULs and creating new
173string_list_items that point into the original string (the original
174string must therefore not be modified or freed while the `string_list`
175is in use).
176
177
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178Data structures
179---------------
180
181* `struct string_list_item`
182
0dda1d1e 183Represents an item of the list. The `string` member is a pointer to the
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184string, and you may use the `util` member for any purpose, if you want.
185
186* `struct string_list`
187
188Represents the list itself.
189
190. The array of items are available via the `items` member.
191. The `nr` member contains the number of items stored in the list.
192. The `alloc` member is used to avoid reallocating at every insertion.
193 You should not tamper with it.
194. Setting the `strdup_strings` member to 1 will strdup() the strings
195 before adding them, see above.