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, 4 insertions, 4 deletions

diff --git a/flood.c b/flood.c
index 1262be8..247c509 100644
--- a/flood.c
+++ b/flood.c
@@ -830,19 +830,19 @@ static char *interpret_move(const game_state *state, game_ui *ui,
     } else if (button == CURSOR_LEFT && ui->cx > 0) {
         ui->cx--;
         ui->cursor_visible = TRUE;
-        return "";
+        return UI_UPDATE;
     } else if (button == CURSOR_RIGHT && ui->cx+1 < w) {
         ui->cx++;
         ui->cursor_visible = TRUE;
-        return "";
+        return UI_UPDATE;
     } else if (button == CURSOR_UP && ui->cy > 0) {
         ui->cy--;
         ui->cursor_visible = TRUE;
-        return "";
+        return UI_UPDATE;
     } else if (button == CURSOR_DOWN && ui->cy+1 < h) {
         ui->cy++;
         ui->cursor_visible = TRUE;
-        return "";
+        return UI_UPDATE;
     } else if (button == CURSOR_SELECT) {
         tx = ui->cx;
         ty = ui->cy;