C++使用初始化列表的方式来初始化字段的方法

class ScreenRecoveryUI : public RecoveryUI { public:  ScreenRecoveryUI();  void Init();  void SetLocale(const char* locale);  // overall recovery state ("background image")  void SetBackground(Icon icon);  // progress indicator  void SetProgressType(ProgressType type);  void ShowProgress(float portion, float seconds);  void SetProgress(float fraction);  void SetStage(int current, int max);  // text log  void ShowText(bool visible);  bool IsTextVisible();  bool WasTextEverVisible();  // printing messages  void Print(const char* fmt, ...) __printflike(2, 3);  void ShowFile(const char* filename);  // menu display  void StartMenu(const char* const * headers, const char* const * items,          int initial_selection);  int SelectMenu(int sel);  void EndMenu();  void KeyLongPress(int);  void Redraw();  enum UIElement {    HEADER, MENU, MENU_SEL_BG, MENU_SEL_BG_ACTIVE, MENU_SEL_FG, LOG, TEXT_FILL, INFO  };  void SetColor(UIElement e); private:  Icon currentIcon;  int installingFrame;  const char* locale;  bool rtl_locale;  pthread_mutex_t updateMutex;  GRSurface* backgroundIcon[5];  GRSurface* backgroundText[5];  GRSurface** installation;  GRSurface* progressBarEmpty;  GRSurface* progressBarFill;  GRSurface* stageMarkerEmpty;  GRSurface* stageMarkerFill;  ProgressType progressBarType;  float progressScopeStart, progressScopeSize, progress;  double progressScopeTime, progressScopeDuration;  // true when both graphics pages are the same (except for the progress bar).  bool pagesIdentical;  size_t text_cols_, text_rows_;  // Log text overlay, displayed when a magic key is pressed.  char** text_;  size_t text_col_, text_row_, text_top_;  bool show_text;  bool show_text_ever;  // has show_text ever been true?  char** menu_;  const char* const* menu_headers_;  bool show_menu;  int menu_items, menu_sel;  // An alternate text screen, swapped with 'text_' when we're viewing a log file.  char** file_viewer_text_;  pthread_t progress_thread_;  int animation_fps;  int installing_frames;  int iconX, iconY;  int stage, max_stage;  void draw_background_locked(Icon icon);  void draw_progress_locked();  void draw_screen_locked();  void update_screen_locked();  void update_progress_locked();  static void* ProgressThreadStartRoutine(void* data);  void ProgressThreadLoop();  void ShowFile(FILE*);  void PutChar(char);  void ClearText();  void DrawHorizontalRule(int* y);  void DrawTextLine(int* y, const char* line, bool bold);  void DrawTextLines(int* y, const char* const* lines);  void LoadBitmap(const char* filename, GRSurface** surface);  void LoadBitmapArray(const char* filename, int* frames, GRSurface*** surface);  void LoadLocalizedBitmap(const char* filename, GRSurface** surface);};

ScreenRecoveryUI::ScreenRecoveryUI() :  currentIcon(NONE),  installingFrame(0),  locale(nullptr),  rtl_locale(false),  progressBarType(EMPTY),  progressScopeStart(0),  progressScopeSize(0),  progress(0),  pagesIdentical(false),  text_cols_(0),  text_rows_(0),  text_(nullptr),  text_col_(0),  text_row_(0),  text_top_(0),  show_text(false),  show_text_ever(false),  menu_(nullptr),  show_menu(false),  menu_items(0),  menu_sel(0),  file_viewer_text_(nullptr),  animation_fps(20),  installing_frames(-1),  stage(-1),  max_stage(-1) {  for (int i = 0; i < 5; i++) {    backgroundIcon[i] = nullptr;  }  pthread_mutex_init(&updateMutex, nullptr);}

class RecoveryUI { public:  RecoveryUI();  virtual ~RecoveryUI() { }  // Initialize the object; called before anything else.  virtual void Init();  // Show a stage indicator. Call immediately after Init().  virtual void SetStage(int current, int max) = 0;  // After calling Init(), you can tell the UI what locale it is operating in.  virtual void SetLocale(const char* locale) = 0;  // Set the overall recovery state ("background image").  enum Icon { NONE, INSTALLING_UPDATE, ERASING, NO_COMMAND, ERROR };  virtual void SetBackground(Icon icon) = 0;  // --- progress indicator ---  enum ProgressType { EMPTY, INDETERMINATE, DETERMINATE };  virtual void SetProgressType(ProgressType determinate) = 0;  // Show a progress bar and define the scope of the next operation:  //  portion - fraction of the progress bar the next operation will use  //  seconds - expected time interval (progress bar moves at this minimum rate)  virtual void ShowProgress(float portion, float seconds) = 0;  // Set progress bar position (0.0 - 1.0 within the scope defined  // by the last call to ShowProgress).  virtual void SetProgress(float fraction) = 0;  // --- text log ---  virtual void ShowText(bool visible) = 0;  virtual bool IsTextVisible() = 0;  virtual bool WasTextEverVisible() = 0;  // Write a message to the on-screen log (shown if the user has  // toggled on the text display).  virtual void Print(const char* fmt, ...) __printflike(2, 3) = 0;  virtual void ShowFile(const char* filename) = 0;  // --- key handling ---  // Wait for a key and return it. May return -1 after timeout.  virtual int WaitKey();  virtual bool IsKeyPressed(int key);  virtual bool IsLongPress();  // Returns true if you have the volume up/down and power trio typical  // of phones and tablets, false otherwise.  virtual bool HasThreeButtons();  // Erase any queued-up keys.  virtual void FlushKeys();  // Called on each key press, even while operations are in progress.  // Return value indicates whether an immediate operation should be  // triggered (toggling the display, rebooting the device), or if  // the key should be enqueued for use by the main thread.  enum KeyAction { ENQUEUE, TOGGLE, REBOOT, IGNORE };  virtual KeyAction CheckKey(int key, bool is_long_press);  // Called when a key is held down long enough to have been a  // long-press (but before the key is released). This means that  // if the key is eventually registered (released without any other  // keys being pressed in the meantime), CheckKey will be called with  // 'is_long_press' true.  virtual void KeyLongPress(int key);  // Normally in recovery there's a key sequence that triggers  // immediate reboot of the device, regardless of what recovery is  // doing (with the default CheckKey implementation, it's pressing  // the power button 7 times in row). Call this to enable or  // disable that feature. It is enabled by default.  virtual void SetEnableReboot(bool enabled);  // --- menu display ---  // Display some header text followed by a menu of items, which appears  // at the top of the screen (in place of any scrolling ui_print()  // output, if necessary).  virtual void StartMenu(const char* const * headers, const char* const * items,              int initial_selection) = 0;  // Set the menu highlight to the given index, wrapping if necessary.  // Returns the actual item selected.  virtual int SelectMenu(int sel) = 0;  // End menu mode, resetting the text overlay so that ui_print()  // statements will be displayed.  virtual void EndMenu() = 0;protected:  void EnqueueKey(int key_code);private:  // Key event input queue  pthread_mutex_t key_queue_mutex;  pthread_cond_t key_queue_cond;  int key_queue[256], key_queue_len;  char key_pressed[KEY_MAX + 1];   // under key_queue_mutex  int key_last_down;         // under key_queue_mutex  bool key_long_press;        // under key_queue_mutex  int key_down_count;        // under key_queue_mutex  bool enable_reboot;        // under key_queue_mutex  int rel_sum;  int consecutive_power_keys;  int last_key;  bool has_power_key;  bool has_up_key;  bool has_down_key;  struct key_timer_t {    RecoveryUI* ui;    int key_code;    int count;  };  pthread_t input_thread_;  void OnKeyDetected(int key_code);  static int InputCallback(int fd, uint32_t epevents, void* data);  int OnInputEvent(int fd, uint32_t epevents);  void ProcessKey(int key_code, int updown);  bool IsUsbConnected();  static void* time_key_helper(void* cookie);  void time_key(int key_code, int count);};ui.cpp中，也是采用字段初始化的方式来实现构造函数：RecoveryUI::RecoveryUI()    : key_queue_len(0),     key_last_down(-1),     key_long_press(false),     key_down_count(0),     enable_reboot(true),     consecutive_power_keys(0),     last_key(-1),     has_power_key(false),     has_up_key(false),     has_down_key(false) {  pthread_mutex_init(&key_queue_mutex, nullptr);  pthread_cond_init(&key_queue_cond, nullptr);  memset(key_pressed, 0, sizeof(key_pressed));}

#include <iostream>using namespace std ;class ScreenRecoveryUI { private : int r , g , b ;  char buffer[10] ; char *p ; public : ScreenRecoveryUI(); void setvalue(int a , int b , int c); void print();};//使用初始化列表的方式初始化构造函数里的私有环境变量 ScreenRecoveryUI::ScreenRecoveryUI(): r(0), g(0), b(0), p(nullptr){ for(int i = 0 ; i < 10 ; i++){ buffer[i] = 0 ; }} void ScreenRecoveryUI::setvalue(int a ,int b , int c){ this->r = a ;  this->g = b ;  this->b = c ;}void ScreenRecoveryUI::print(){ cout << "r:" << this->r << endl << "g:" << this->g << endl << "b:" << b << endl ; }int main(void){ ScreenRecoveryUI screen ;  screen.setvalue(255,255,0); screen.print(); return 0 ;}