introduce CHECKOUT_INIT

Add a static initializer for struct checkout and use it throughout the
code base.  It's shorter, avoids a memset(3) call and makes sure the
base_dir member is initialized to a valid (empty) string.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

apply.c

@@ -3334,10 +3334,8 @@ static void prepare_fn_table(struct apply_state *state, struct patch *patch)
 static int checkout_target(struct index_state *istate,
 			   struct cache_entry *ce, struct stat *st)
 {
-	struct checkout costate;
+	struct checkout costate = CHECKOUT_INIT;
 
-	memset(&costate, 0, sizeof(costate));
-	costate.base_dir = "";
 	costate.refresh_cache = 1;
 	costate.istate = istate;
 	if (checkout_entry(ce, &costate, NULL) || lstat(ce->name, st))

builtin/checkout-index.c

@@ -16,7 +16,7 @@ static int checkout_stage; /* default to checkout stage0 */
 static int to_tempfile;
 static char topath[4][TEMPORARY_FILENAME_LENGTH + 1];
 
-static struct checkout state;
+static struct checkout state = CHECKOUT_INIT;
 
 static void write_tempfile_record(const char *name, const char *prefix)
 {

builtin/checkout.c

@@ -239,7 +239,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 			  const char *revision)
 {
 	int pos;
-	struct checkout state;
+	struct checkout state = CHECKOUT_INIT;
 	static char *ps_matched;
 	struct object_id rev;
 	struct commit *head;
@@ -352,7 +352,6 @@ static int checkout_paths(const struct checkout_opts *opts,
 		return 1;
 
 	/* Now we are committed to check them out */
-	memset(&state, 0, sizeof(state));
 	state.force = 1;
 	state.refresh_cache = 1;
 	state.istate = &the_index;

cache.h

@@ -1354,6 +1354,7 @@ struct checkout {
 		 not_new:1,
 		 refresh_cache:1;
 };
+#define CHECKOUT_INIT { NULL, "" }
 
 #define TEMPORARY_FILENAME_LENGTH 25
 extern int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *topath);

unpack-trees.c

@@ -1094,12 +1094,10 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	int i, ret;
 	static struct cache_entry *dfc;
 	struct exclude_list el;
-	struct checkout state;
+	struct checkout state = CHECKOUT_INIT;
 
 	if (len > MAX_UNPACK_TREES)
 		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
-	memset(&state, 0, sizeof(state));
-	state.base_dir = "";
 	state.force = 1;
 	state.quiet = 1;
 	state.refresh_cache = 1;