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+#ifndef STRING_LIST_H
+#define STRING_LIST_H
+
+/**
+ * The string_list API offers a data structure and functions to handle
+ * sorted and unsorted arrays of strings.  A "sorted" list is one whose
+ * entries are sorted by string value in `strcmp()` order.
+ *
+ * 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`,
+ *   `string_list_append_nodup`, `string_list_insert`,
+ *   `string_list_split`, and/or `string_list_split_in_place`.
+ *
+ * . 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 `string_list_sort`.
+ *
+ * . Can remove duplicate items from a sorted list using
+ *   `string_list_remove_duplicates`.
+ *
+ * . Can remove individual items of an unsorted list using
+ *   `unsorted_string_list_delete_item`.
+ *
+ * . Can remove items not matching a criterion from a sorted or unsorted
+ *   list using `filter_string_list`, or remove empty strings using
+ *   `string_list_remove_empty_items`.
+ *
+ * . Finally it should free the list using `string_list_clear`.
+ *
+ * Example:
+ *
+ *     struct string_list list = STRING_LIST_INIT_NODUP;
+ *     int i;
+ *
+ *     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).
+ */
+
+/**
+ * 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_item {
+	char *string;
+	void *util;
+};
+
+typedef int (*compare_strings_fn)(const char *, const char *);
+
+/**
+ * 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.
+ * . The `compare_strings_fn` member is used to specify a custom compare
+ *   function, otherwise `strcmp()` is used as the default function.
+ */
+struct string_list {
+	struct string_list_item *items;
+	unsigned int nr, alloc;
+	unsigned int strdup_strings:1;
+	compare_strings_fn cmp; /* NULL uses strcmp() */
+};
+
+#define STRING_LIST_INIT_NODUP { NULL, 0, 0, 0, NULL }
+#define STRING_LIST_INIT_DUP   { NULL, 0, 0, 1, NULL }
+
+/* General functions which work with both sorted and unsorted lists. */
+
+/**
+ * Initialize the members of the string_list, set `strdup_strings`
+ * member according to the value of the second parameter.
+ */
+void string_list_init(struct string_list *list, int strdup_strings);
+
+/** Callback function type for for_each_string_list */
+typedef int (*string_list_each_func_t)(struct string_list_item *, void *);
+
+/**
+ * Apply `want` to each item in `list`, retaining only the ones for which
+ * the function returns true.  If `free_util` is true, call free() on
+ * the util members of any items that have to be deleted.  Preserve
+ * the order of the items that are retained.
+ */
+void filter_string_list(struct string_list *list, int free_util,
+			string_list_each_func_t want, void *cb_data);
+
+/**
+ * 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.
+ */
+void string_list_clear(struct string_list *list, int free_util);
+
+/**
+ * Callback type for `string_list_clear_func`.  The string associated
+ * with the util pointer is passed as the second argument
+ */
+typedef void (*string_list_clear_func_t)(void *p, const char *str);
+
+/** Call a custom clear function on each util pointer */
+void string_list_clear_func(struct string_list *list, string_list_clear_func_t clearfunc);
+
+/**
+ * Apply `func` to each item. If `func` returns nonzero, the
+ * iteration aborts and the return value is propagated.
+ */
+int for_each_string_list(struct string_list *list,
+			 string_list_each_func_t func, void *cb_data);
+
+/** Iterate over each item, as a macro. */
+#define for_each_string_list_item(item,list)            \
+	for (item = (list)->items;                      \
+	     item && item < (list)->items + (list)->nr; \
+	     ++item)
+
+/**
+ * Remove any empty strings from the list.  If free_util is true, call
+ * free() on the util members of any items that have to be deleted.
+ * Preserve the order of the items that are retained.
+ */
+void string_list_remove_empty_items(struct string_list *list, int free_util);
+
+/* Use these functions only on sorted lists: */
+
+/** Determine if the string_list has a given string or not. */
+int string_list_has_string(const struct string_list *list, const char *string);
+int string_list_find_insert_index(const struct string_list *list, const char *string,
+				  int negative_existing_index);
+
+/**
+ * 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. If the given
+ * string already exists the insertion will be skipped and the pointer
+ * to the existing item returned.
+ *
+ * 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 = ...;`.
+ */
+struct string_list_item *string_list_insert(struct string_list *list, const char *string);
+
+/**
+ * Remove the given string from the sorted list.  If the string
+ * doesn't exist, the list is not altered.
+ */
+void string_list_remove(struct string_list *list, const char *string,
+			int free_util);
+
+/**
+ * Check if the given string is part of a sorted list. If it is part of the list,
+ * return the coresponding string_list_item, NULL otherwise.
+ */
+struct string_list_item *string_list_lookup(struct string_list *list, const char *string);
+
+/*
+ * Remove all but the first of consecutive entries with the same
+ * string value.  If free_util is true, call free() on the util
+ * members of any items that have to be deleted.
+ */
+void string_list_remove_duplicates(struct string_list *sorted_list, int free_util);
+
+
+/* Use these functions only on unsorted lists: */
+
+/**
+ * Add string to the end of list.  If list->strdup_string is set, then
+ * string is copied; otherwise the new string_list_entry refers to the
+ * input string.
+ */
+struct string_list_item *string_list_append(struct string_list *list, const char *string);
+
+/**
+ * Like string_list_append(), except string is never copied.  When
+ * list->strdup_strings is set, this function can be used to hand
+ * ownership of a malloc()ed string to list without making an extra
+ * copy.
+ */
+struct string_list_item *string_list_append_nodup(struct string_list *list, char *string);
+
+/**
+ * Sort the list's entries by string value in `strcmp()` order.
+ */
+void string_list_sort(struct string_list *list);
+
+/**
+ * Like `string_list_has_string()` but for unsorted lists. Linear in
+ * size of the list.
+ */
+int unsorted_string_list_has_string(struct string_list *list, const char *string);
+
+/**
+ * Like `string_list_lookup()` but for unsorted lists. Linear in size
+ * of the list.
+ */
+struct string_list_item *unsorted_string_list_lookup(struct string_list *list,
+						     const char *string);
+/**
+ * Remove an item from 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 third parameter controls if the `util`
+ * pointer of the items should be freed or not.
+ */
+void unsorted_string_list_delete_item(struct string_list *list, int i, int free_util);
+
+/**
+ * Split string into substrings on character `delim` and append the
+ * substrings to `list`.  The input string is not modified.
+ * list->strdup_strings must be set, as new memory needs to be
+ * allocated to hold the substrings.  If maxsplit is non-negative,
+ * then split at most maxsplit times.  Return the number of substrings
+ * appended to list.
+ *
+ * Examples:
+ *   string_list_split(l, "foo:bar:baz", ':', -1) -> ["foo", "bar", "baz"]
+ *   string_list_split(l, "foo:bar:baz", ':', 0) -> ["foo:bar:baz"]
+ *   string_list_split(l, "foo:bar:baz", ':', 1) -> ["foo", "bar:baz"]
+ *   string_list_split(l, "foo:bar:", ':', -1) -> ["foo", "bar", ""]
+ *   string_list_split(l, "", ':', -1) -> [""]
+ *   string_list_split(l, ":", ':', -1) -> ["", ""]
+ */
+int string_list_split(struct string_list *list, const char *string,
+		      int delim, int maxsplit);
+
+/*
+ * Like string_list_split(), except that string is split in-place: the
+ * delimiter characters in string are overwritten with NULs, and the
+ * new string_list_items point into string (which therefore must not
+ * be modified or freed while the string_list is in use).
+ * list->strdup_strings must *not* be set.
+ */
+int string_list_split_in_place(struct string_list *list, char *string,
+			       int delim, int maxsplit);
+#endif /* STRING_LIST_H */