Ensure that the whole modified text is returned from DrawTextExA.

dlls/user/text.c

@@ -334,6 +334,13 @@ static void TEXT_DrawUnderscore (HDC hdc, int x, int y, const WCHAR *str, int of
 
 /***********************************************************************
  *           DrawTextExW    (USER32.@)
+ *
+ * The documentation on the extra space required for DT_MODIFYSTRING at MSDN
+ * is not quite complete, especially with regard to \0.  We will assume that
+ * the returned string could have a length of up to i_count+3 and also have
+ * a trailing \0 (which would be 4 more than a not-null-terminated string but
+ * 3 more than a null-terminated string).  If this is not so then increase 
+ * the allowance in DrawTextExA.
  */
 #define MAX_STATIC_BUFFER 1024
 INT WINAPI DrawTextExW( HDC hdc, LPWSTR str, INT i_count,
@@ -539,24 +546,51 @@ INT WINAPI DrawTextExW( HDC hdc, LPWSTR str, INT i_count,
 
 /***********************************************************************
  *           DrawTextExA    (USER32.@)
+ *
+ * If DT_MODIFYSTRING is specified then there must be room for up to 
+ * 4 extra characters.  We take great care about just how much modified
+ * string we return.
  */
 INT WINAPI DrawTextExA( HDC hdc, LPSTR str, INT count,
                         LPRECT rect, UINT flags, LPDRAWTEXTPARAMS dtp )
 {
    WCHAR *wstr;
+   WCHAR *p;
    INT ret = 0;
+   int i;
    DWORD wcount;
+   DWORD wmax;
+   DWORD amax;
 
    if (count == -1) count = strlen(str);
    if (!count) return 0;
    wcount = MultiByteToWideChar( CP_ACP, 0, str, count, NULL, 0 );
-   wstr = HeapAlloc(GetProcessHeap(), 0, wcount * sizeof(WCHAR));
+   wmax = wcount;
+   amax = count;
+   if (flags & DT_MODIFYSTRING)
+   {
+        wmax += 4;
+        amax += 4;
+   }
+   wstr = HeapAlloc(GetProcessHeap(), 0, wmax * sizeof(WCHAR));
    if (wstr)
    {
        MultiByteToWideChar( CP_ACP, 0, str, count, wstr, wcount );
+       if (flags & DT_MODIFYSTRING)
+           for (i=4, p=wstr+wcount; i--; p++) *p=0xFFFE;
+           /* Initialise the extra characters so that we can see which ones
+            * change.  U+FFFE is guaranteed to be not a unicode character and
+            * so will not be generated by DrawTextEx itself.
+            */
        ret = DrawTextExW( hdc, wstr, wcount, rect, flags, NULL );
        if (flags & DT_MODIFYSTRING)
-            WideCharToMultiByte( CP_ACP, 0, wstr, -1, str, count, NULL, NULL );
+       {
+            /* Unfortunately the returned string may contain multiple \0s
+             * and so we need to measure it ourselves.
+             */
+            for (i=4, p=wstr+wcount; i-- && *p != 0xFFFE; p++) wcount++;
+            WideCharToMultiByte( CP_ACP, 0, wstr, wcount, str, amax, NULL, NULL );
+       }
        HeapFree(GetProcessHeap(), 0, wstr);
    }
    return ret;