string-list: add string_list initializer helper function

The string-list API has STRING_LIST_INIT_* macros to be used
to define variables with initializers, but lacks functions
to initialize an uninitialized piece of memory to be used as
a string-list at the run-time.
Introduce `string_list_init()` function for that.

Signed-off-by: Tanay Abhra <tanayabh@gmail.com>
Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-string-list.txt

@@ -68,6 +68,11 @@ Functions
 
 * General ones (works with sorted and unsorted lists as well)
 
+`string_list_init`::
+
+	Initialize the members of the string_list, set `strdup_strings`
+	member according to the value of the second parameter.
+
 `filter_string_list`::
 
 	Apply a function to each item in a list, retaining only the

string-list.c

@@ -1,6 +1,12 @@
 #include "cache.h"
 #include "string-list.h"
 
+void string_list_init(struct string_list *list, int strdup_strings)
+{
+	memset(list, 0, sizeof(*list));
+	list->strdup_strings = strdup_strings;
+}
+
 /* if there is no exact match, point to the index where the entry could be
  * inserted */
 static int get_entry_index(const struct string_list *list, const char *string,

string-list.h

@@ -18,6 +18,8 @@ struct string_list {
 #define STRING_LIST_INIT_NODUP { NULL, 0, 0, 0, NULL }
 #define STRING_LIST_INIT_DUP   { NULL, 0, 0, 1, NULL }
 
+void string_list_init(struct string_list *list, int strdup_strings);
+
 void print_string_list(const struct string_list *p, const char *text);
 void string_list_clear(struct string_list *list, int free_util);