Use member initialization in 'struct ui'

This changes 'struct ui' to use member initialization.  This is
simpler to understand.

gdb/top.c

@@ -295,26 +295,17 @@ unbuffer_stream (FILE *stream)
 /* See top.h.  */
 
 ui::ui (FILE *instream_, FILE *outstream_, FILE *errstream_)
-  : next (nullptr),
+  : num (++highest_ui_num),
-    num (++highest_ui_num),
-    call_readline (nullptr),
-    input_handler (nullptr),
-    command_editing (0),
-    interp_info (nullptr),
-    async (0),
-    secondary_prompt_depth (0),
     stdin_stream (instream_),
     instream (instream_),
     outstream (outstream_),
     errstream (errstream_),
     input_fd (fileno (instream)),
     m_input_interactive_p (ISATTY (instream)),
-    prompt_state (PROMPT_NEEDED),
     m_gdb_stdout (new pager_file (new stdio_file (outstream))),
     m_gdb_stdin (new stdio_file (instream)),
     m_gdb_stderr (new stderr_file (errstream)),
-    m_gdb_stdlog (m_gdb_stderr),
+    m_gdb_stdlog (m_gdb_stderr)
-    m_current_uiout (nullptr)
 {
   buffer_init (&line_buffer);
 

gdb/top.h

@@ -61,7 +61,7 @@ struct ui
   DISABLE_COPY_AND_ASSIGN (ui);
 
   /* Pointer to next in singly-linked list.  */
-  struct ui *next;
+  struct ui *next = nullptr;
 
   /* Convenient handle (UI number).  Unique across all UIs.  */
   int num;
@@ -76,19 +76,19 @@ struct ui
      point of invocation.  In the special case in which the character
      read is newline, the function invokes the INPUT_HANDLER callback
      (see below).  */
-  void (*call_readline) (gdb_client_data);
+  void (*call_readline) (gdb_client_data) = nullptr;
 
   /* The function to invoke when a complete line of input is ready for
      processing.  */
-  void (*input_handler) (gdb::unique_xmalloc_ptr<char> &&);
+  void (*input_handler) (gdb::unique_xmalloc_ptr<char> &&) = nullptr;
 
   /* True if this UI is using the readline library for command
      editing; false if using GDB's own simple readline emulation, with
      no editing support.  */
-  int command_editing;
+  int command_editing = 0;
 
   /* Each UI has its own independent set of interpreters.  */
-  struct ui_interp_info *interp_info;
+  struct ui_interp_info *interp_info = nullptr;
 
   /* True if the UI is in async mode, false if in sync mode.  If in
      sync mode, a synchronous execution command (e.g, "next") does not
@@ -98,11 +98,11 @@ struct ui
      the top event loop.  For the main UI, this starts out disabled,
      until all the explicit command line arguments (e.g., `gdb -ex
      "start" -ex "next"') are processed.  */
-  int async;
+  int async = 0;
 
   /* The number of nested readline secondary prompts that are
      currently active.  */
-  int secondary_prompt_depth;
+  int secondary_prompt_depth = 0;
 
   /* The UI's stdin.  Set to stdin for the main UI.  */
   FILE *stdin_stream;
@@ -128,7 +128,7 @@ struct ui
   bool m_input_interactive_p;
 
   /* See enum prompt_state's description.  */
-  enum prompt_state prompt_state;
+  enum prompt_state prompt_state = PROMPT_NEEDED;
 
   /* The fields below that start with "m_" are "private".  They're
      meant to be accessed through wrapper macros that make them look
@@ -146,7 +146,7 @@ struct ui
   struct ui_file *m_gdb_stdlog;
 
   /* The current ui_out.  */
-  struct ui_out *m_current_uiout;
+  struct ui_out *m_current_uiout = nullptr;
 
   /* Register the UI's input file descriptor in the event loop.  */
   void register_file_handler ();