[thirdparty/git.git] / Documentation / technical / api-string-list.txt

string-list API
===============

The string_list API offers a data structure and functions to handle sorted
and unsorted string lists.

The 'string_list' struct used to be called 'path_list', but was renamed
because it is not specific to paths.

The caller:

. Allocates and clears a `struct string_list` variable.

. Initializes the members. You might want to set the flag `strdup_strings`
  if the strings should be strdup()ed. For example, this is necessary
  when you add something like git_path("..."), since that function returns
  a static buffer that will change with the next call to git_path().
+
If you need something advanced, you can manually malloc() the `items`
member (you need this if you add things later) and you should set the
`nr` and `alloc` members in that case, too.

. Adds new items to the list, using `string_list_append` or
  `string_list_insert`.

. Can check if a string is in the list using `string_list_has_string` or
  `unsorted_string_list_has_string` and get it from the list using
  `string_list_lookup` for sorted lists.

. Can sort an unsorted list using `sort_string_list`.

. Finally it should free the list using `string_list_clear`.

Example:

----
struct string_list list;
int i;

memset(&list, 0, sizeof(struct string_list));
string_list_append(&list, "foo");
string_list_append(&list, "bar");
for (i = 0; i < list.nr; i++)
	printf("%s\n", list.items[i].string)
----

NOTE: It is more efficient to build an unsorted list and sort it
afterwards, instead of building a sorted list (`O(n log n)` instead of
`O(n^2)`).
+
However, if you use the list to check if a certain string was added
already, you should not do that (using unsorted_string_list_has_string()),
because the complexity would be quadratic again (but with a worse factor).

Functions
---------

* General ones (works with sorted and unsorted lists as well)

`print_string_list`::

	Dump a string_list to stdout, useful mainly for debugging purposes. It
	can take an optional header argument and it writes out the
	string-pointer pairs of the string_list, each one in its own line.

`string_list_clear`::

	Free a string_list. The `string` pointer of the items will be freed in
	case the `strdup_strings` member of the string_list is set. The second
	parameter controls if the `util` pointer of the items should be freed
	or not.

* Functions for sorted lists only

`string_list_has_string`::

	Determine if the string_list has a given string or not.

`string_list_insert`::

	Insert a new element to the string_list. The returned pointer can be
	handy if you want to write something to the `util` pointer of the
	string_list_item containing the just added string.
+
Since this function uses xrealloc() (which die()s if it fails) if the
list needs to grow, it is safe not to check the pointer. I.e. you may
write `string_list_insert(...)->util = ...;`.

`string_list_lookup`::

	Look up a given string in the string_list, returning the containing
	string_list_item. If the string is not found, NULL is returned.

* Functions for unsorted lists only

`string_list_append`::

	Append a new string to the end of the string_list.

`sort_string_list`::

	Make an unsorted list sorted.

`unsorted_string_list_has_string`::

	It's like `string_list_has_string()` but for unsorted lists.

`unsorted_string_list_lookup`::

	It's like `string_list_lookup()` but for unsorted lists.
+
The above two functions need to look through all items, as opposed to their
counterpart for sorted lists, which performs a binary search.

Data structures
---------------

* `struct string_list_item`

Represents an item of the list. The `string` member is a pointer to the
string, and you may use the `util` member for any purpose, if you want.

* `struct string_list`

Represents the list itself.

. The array of items are available via the `items` member.
. The `nr` member contains the number of items stored in the list.
. The `alloc` member is used to avoid reallocating at every insertion.
  You should not tamper with it.
. Setting the `strdup_strings` member to 1 will strdup() the strings
  before adding them, see above.
Commit	Line	Data
c455c87c JS	1	string-list API
	2	===============
	3
	4	The string_list API offers a data structure and functions to handle sorted
	5	and unsorted string lists.
	6
	7	The 'string_list' struct used to be called 'path_list', but was renamed
	8	because it is not specific to paths.
	9
	10	The 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	+
	19	If you need something advanced, you can manually malloc() the `items`
	20	member (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
	32	. Finally it should free the list using `string_list_clear`.
	33
	34	Example:
	35
	36	----
	37	struct string_list list;
	38	int i;
	39
	40	memset(&list, 0, sizeof(struct string_list));
1d2f80fa JP	41	string_list_append(&list, "foo");
1d2f80fa JP	42	string_list_append(&list, "bar");
c455c87c	43	for (i = 0; i < list.nr; i++)
0dda1d1e	44	printf("%s\n", list.items[i].string)
c455c87c JS	45	----
	46
	47	NOTE: It is more efficient to build an unsorted list and sort it
	48	afterwards, instead of building a sorted list (`O(n log n)` instead of
	49	`O(n^2)`).
	50	+
	51	However, if you use the list to check if a certain string was added
	52	already, you should not do that (using unsorted_string_list_has_string()),
	53	because the complexity would be quadratic again (but with a worse factor).
	54
	55	Functions
	56	---------
	57
	58	* General ones (works with sorted and unsorted lists as well)
	59
	60	`print_string_list`::
	61
	62	Dump a string_list to stdout, useful mainly for debugging purposes. It
	63	can take an optional header argument and it writes out the
	64	string-pointer pairs of the string_list, each one in its own line.
	65
	66	`string_list_clear`::
	67
	68	Free a string_list. The `string` pointer of the items will be freed in
	69	case the `strdup_strings` member of the string_list is set. The second
	70	parameter controls if the `util` pointer of the items should be freed
	71	or not.
	72
	73	* Functions for sorted lists only
	74
	75	`string_list_has_string`::
	76
	77	Determine if the string_list has a given string or not.
	78
	79	`string_list_insert`::
	80
	81	Insert a new element to the string_list. The returned pointer can be
	82	handy if you want to write something to the `util` pointer of the
	83	string_list_item containing the just added string.
	84	+
	85	Since this function uses xrealloc() (which die()s if it fails) if the
	86	list needs to grow, it is safe not to check the pointer. I.e. you may
	87	write `string_list_insert(...)->util = ...;`.
	88
	89	`string_list_lookup`::
	90
	91	Look up a given string in the string_list, returning the containing
	92	string_list_item. If the string is not found, NULL is returned.
	93
	94	* Functions for unsorted lists only
	95
	96	`string_list_append`::
	97
	98	Append a new string to the end of the string_list.
	99
	100	`sort_string_list`::
	101
	102	Make an unsorted list sorted.
	103
	104	`unsorted_string_list_has_string`::
	105
	106	It's like `string_list_has_string()` but for unsorted lists.
e2421480 SB	107
	108	`unsorted_string_list_lookup`::
	109
	110	It's like `string_list_lookup()` but for unsorted lists.
c455c87c	111	+
e2421480	112	The above two functions need to look through all items, as opposed to their
c455c87c JS	113	counterpart for sorted lists, which performs a binary search.
	114
	115	Data structures
	116	---------------
	117
	118	* `struct string_list_item`
	119
0dda1d1e	120	Represents an item of the list. The `string` member is a pointer to the
c455c87c JS	121	string, and you may use the `util` member for any purpose, if you want.
	122
	123	* `struct string_list`
	124
	125	Represents the list itself.
	126
	127	. The array of items are available via the `items` member.
	128	. The `nr` member contains the number of items stored in the list.
	129	. The `alloc` member is used to avoid reallocating at every insertion.
	130	You should not tamper with it.
	131	. Setting the `strdup_strings` member to 1 will strdup() the strings
	132	before adding them, see above.