New name UI_UPDATE for interpret_move's return "".

Now midend.c directly tests the returned pointer for equality to this
value, instead of checking whether it's the empty string.

A minor effect of this is that games may now return a dynamically
allocated empty string from interpret_move() and treat it as just
another legal move description. But I don't expect anyone to be
perverse enough to actually do that! The main purpose is that it
avoids returning a string literal from a function whose return type is
a pointer to _non-const_ char, i.e. we are now one step closer to
being able to make this code base clean under -Wwrite-strings.

1 files changed, 5 insertions, 5 deletions

diff --git a/blackbox.c b/blackbox.c
index b334cf7..422b752 100644
--- a/blackbox.c
+++ b/blackbox.c
@@ -902,7 +902,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         ui->cur_x = cx;
         ui->cur_y = cy;
         ui->cur_visible = 1;
-        return "";
+        return UI_UPDATE;
     }
 
     if (button == LEFT_BUTTON || button == RIGHT_BUTTON) {
@@ -912,7 +912,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         wouldflash = 1;
     } else if (button == LEFT_RELEASE) {
         ui->flash_laser = 0;
-        return "";
+        return UI_UPDATE;
     } else if (IS_CURSOR_SELECT(button)) {
         if (ui->cur_visible) {
             gx = ui->cur_x;
@@ -921,7 +921,7 @@ static char *interpret_move(const game_state *state, game_ui *ui,
             wouldflash = 2;
         } else {
             ui->cur_visible = 1;
-            return "";
+            return UI_UPDATE;
         }
         /* Fix up 'button' for the below logic. */
         if (button == CURSOR_SELECT2) button = RIGHT_BUTTON;
@@ -970,9 +970,9 @@ static char *interpret_move(const game_state *state, game_ui *ui,
 	    return nullret;
         ui->flash_laserno = rangeno;
         ui->flash_laser = wouldflash;
-        nullret = "";
+        nullret = UI_UPDATE;
         if (state->exits[rangeno] != LASER_EMPTY)
-            return "";
+            return UI_UPDATE;
         sprintf(buf, "F%d", rangeno);
         break;