The fourth batch for 1.8.0
[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
23. Adds new items to the list, using `string_list_append` or
24 `string_list_insert`.
25
26. Can check if a string is in the list using `string_list_has_string` or
27 `unsorted_string_list_has_string` and get it from the list using
28 `string_list_lookup` for sorted lists.
29
30. Can sort an unsorted list using `sort_string_list`.
31
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32. Can remove individual items of an unsorted list using
33 `unsorted_string_list_delete_item`.
34
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35. Finally it should free the list using `string_list_clear`.
36
37Example:
38
39----
40struct string_list list;
41int i;
42
43memset(&list, 0, sizeof(struct string_list));
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44string_list_append(&list, "foo");
45string_list_append(&list, "bar");
c455c87c 46for (i = 0; i < list.nr; i++)
0dda1d1e 47 printf("%s\n", list.items[i].string)
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48----
49
50NOTE: It is more efficient to build an unsorted list and sort it
51afterwards, instead of building a sorted list (`O(n log n)` instead of
52`O(n^2)`).
53+
54However, if you use the list to check if a certain string was added
55already, you should not do that (using unsorted_string_list_has_string()),
56because the complexity would be quadratic again (but with a worse factor).
57
58Functions
59---------
60
61* General ones (works with sorted and unsorted lists as well)
62
63`print_string_list`::
64
65 Dump a string_list to stdout, useful mainly for debugging purposes. It
66 can take an optional header argument and it writes out the
67 string-pointer pairs of the string_list, each one in its own line.
68
69`string_list_clear`::
70
71 Free a string_list. The `string` pointer of the items will be freed in
72 case the `strdup_strings` member of the string_list is set. The second
73 parameter controls if the `util` pointer of the items should be freed
74 or not.
75
76* Functions for sorted lists only
77
78`string_list_has_string`::
79
80 Determine if the string_list has a given string or not.
81
82`string_list_insert`::
83
84 Insert a new element to the string_list. The returned pointer can be
85 handy if you want to write something to the `util` pointer of the
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86 string_list_item containing the just added string. If the given
87 string already exists the insertion will be skipped and the
88 pointer to the existing item returned.
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89+
90Since this function uses xrealloc() (which die()s if it fails) if the
91list needs to grow, it is safe not to check the pointer. I.e. you may
92write `string_list_insert(...)->util = ...;`.
93
94`string_list_lookup`::
95
96 Look up a given string in the string_list, returning the containing
97 string_list_item. If the string is not found, NULL is returned.
98
99* Functions for unsorted lists only
100
101`string_list_append`::
102
103 Append a new string to the end of the string_list.
104
105`sort_string_list`::
106
107 Make an unsorted list sorted.
108
109`unsorted_string_list_has_string`::
110
111 It's like `string_list_has_string()` but for unsorted lists.
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112
113`unsorted_string_list_lookup`::
114
115 It's like `string_list_lookup()` but for unsorted lists.
c455c87c 116+
e2421480 117The above two functions need to look through all items, as opposed to their
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118counterpart for sorted lists, which performs a binary search.
119
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120`unsorted_string_list_delete_item`::
121
122 Remove an item from a string_list. The `string` pointer of the items
123 will be freed in case the `strdup_strings` member of the string_list
124 is set. The third parameter controls if the `util` pointer of the
125 items should be freed or not.
126
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127Data structures
128---------------
129
130* `struct string_list_item`
131
0dda1d1e 132Represents an item of the list. The `string` member is a pointer to the
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133string, and you may use the `util` member for any purpose, if you want.
134
135* `struct string_list`
136
137Represents the list itself.
138
139. The array of items are available via the `items` member.
140. The `nr` member contains the number of items stored in the list.
141. The `alloc` member is used to avoid reallocating at every insertion.
142 You should not tamper with it.
143. Setting the `strdup_strings` member to 1 will strdup() the strings
144 before adding them, see above.