C++-对于C++ enum 这个怎么理解

Question

    enum class DirtyFlag
    {
        NONE = 0,
        FIXED_PRIORITY = 1 << 0,
        SCENE_GRAPH_PRIORITY = 1 << 1,
        ALL = FIXED_PRIORITY | SCENE_GRAPH_PRIORITY
    };

Answer 1

没本质区别，其实就像下面的代码，为了统一所以把1写成1<<0。

 #define F_PARSE (1<<0) /* process modem status messages */
#define F_ISSUE (1<<1) /* display /etc/issue */
#define F_RTSCTS (1<<2) /* enable RTS/CTS flow control */
#define F_LOCAL (1<<3) /* force local */
#define F_INITSTRING (1<<4) /* initstring is set */
#define F_WAITCRLF (1<<5) /* wait for CR or LF */
#define F_CUSTISSUE (1<<6) /* give alternative issue file */
#define F_NOPROMPT (1<<7) /* do not ask for login name! */
#define F_LCUC (1<<8) /* support for *LCUC stty modes */
#define F_KEEPSPEED (1<<9) /* follow baud rate from kernel */

Answer 2

这个只是为了和后面的代码风格统一，其实

int a = 1<<0;

和

 int a = 1;

是一样的。