string_list: add a new function, filter_string_list()
[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 individual items of an unsorted list using
34 `unsorted_string_list_delete_item`.
35
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36. Can remove items not matching a criterion from a sorted or unsorted
37 list using `filter_string_list`.
38
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39. Finally it should free the list using `string_list_clear`.
40
41Example:
42
43----
44struct string_list list;
45int i;
46
47memset(&list, 0, sizeof(struct string_list));
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48string_list_append(&list, "foo");
49string_list_append(&list, "bar");
c455c87c 50for (i = 0; i < list.nr; i++)
0dda1d1e 51 printf("%s\n", list.items[i].string)
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52----
53
54NOTE: It is more efficient to build an unsorted list and sort it
55afterwards, instead of building a sorted list (`O(n log n)` instead of
56`O(n^2)`).
57+
58However, if you use the list to check if a certain string was added
59already, you should not do that (using unsorted_string_list_has_string()),
60because the complexity would be quadratic again (but with a worse factor).
61
62Functions
63---------
64
65* General ones (works with sorted and unsorted lists as well)
66
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67`filter_string_list`::
68
69 Apply a function to each item in a list, retaining only the
70 items for which the function returns true. If free_util is
71 true, call free() on the util members of any items that have
72 to be deleted. Preserve the order of the items that are
73 retained.
74
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75`print_string_list`::
76
77 Dump a string_list to stdout, useful mainly for debugging purposes. It
78 can take an optional header argument and it writes out the
79 string-pointer pairs of the string_list, each one in its own line.
80
81`string_list_clear`::
82
83 Free a string_list. The `string` pointer of the items will be freed in
84 case the `strdup_strings` member of the string_list is set. The second
85 parameter controls if the `util` pointer of the items should be freed
86 or not.
87
88* Functions for sorted lists only
89
90`string_list_has_string`::
91
92 Determine if the string_list has a given string or not.
93
94`string_list_insert`::
95
96 Insert a new element to the string_list. The returned pointer can be
97 handy if you want to write something to the `util` pointer of the
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98 string_list_item containing the just added string. If the given
99 string already exists the insertion will be skipped and the
100 pointer to the existing item returned.
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101+
102Since this function uses xrealloc() (which die()s if it fails) if the
103list needs to grow, it is safe not to check the pointer. I.e. you may
104write `string_list_insert(...)->util = ...;`.
105
106`string_list_lookup`::
107
108 Look up a given string in the string_list, returning the containing
109 string_list_item. If the string is not found, NULL is returned.
110
111* Functions for unsorted lists only
112
113`string_list_append`::
114
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115 Append a new string to the end of the string_list. If
116 `strdup_string` is set, then the string argument is copied;
117 otherwise the new `string_list_entry` refers to the input
118 string.
119
120`string_list_append_nodup`::
121
122 Append a new string to the end of the string_list. The new
123 `string_list_entry` always refers to the input string, even if
124 `strdup_string` is set. This function can be used to hand
125 ownership of a malloc()ed string to a `string_list` that has
126 `strdup_string` set.
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127
128`sort_string_list`::
129
130 Make an unsorted list sorted.
131
132`unsorted_string_list_has_string`::
133
134 It's like `string_list_has_string()` but for unsorted lists.
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135
136`unsorted_string_list_lookup`::
137
138 It's like `string_list_lookup()` but for unsorted lists.
c455c87c 139+
e2421480 140The above two functions need to look through all items, as opposed to their
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141counterpart for sorted lists, which performs a binary search.
142
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143`unsorted_string_list_delete_item`::
144
145 Remove an item from a string_list. The `string` pointer of the items
146 will be freed in case the `strdup_strings` member of the string_list
147 is set. The third parameter controls if the `util` pointer of the
148 items should be freed or not.
149
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150`string_list_split`::
151`string_list_split_in_place`::
152
153 Split a string into substrings on a delimiter character and
154 append the substrings to a `string_list`. If `maxsplit` is
155 non-negative, then split at most `maxsplit` times. Return the
156 number of substrings appended to the list.
157+
158`string_list_split` requires a `string_list` that has `strdup_strings`
159set to true; it leaves the input string untouched and makes copies of
160the substrings in newly-allocated memory.
161`string_list_split_in_place` requires a `string_list` that has
162`strdup_strings` set to false; it splits the input string in place,
163overwriting the delimiter characters with NULs and creating new
164string_list_items that point into the original string (the original
165string must therefore not be modified or freed while the `string_list`
166is in use).
167
168
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169Data structures
170---------------
171
172* `struct string_list_item`
173
0dda1d1e 174Represents an item of the list. The `string` member is a pointer to the
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175string, and you may use the `util` member for any purpose, if you want.
176
177* `struct string_list`
178
179Represents the list itself.
180
181. The array of items are available via the `items` member.
182. The `nr` member contains the number of items stored in the list.
183. The `alloc` member is used to avoid reallocating at every insertion.
184 You should not tamper with it.
185. Setting the `strdup_strings` member to 1 will strdup() the strings
186 before adding them, see above.