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