Enum

多使用enum而不是#define

// webcolors.h (third party header)
#define RED   0xFF0000
#define GREEN 0x00FF00
#define BLUE  0x0000FF

// productinfo.h
// The following define product subtypes based on color
#define RED    0
#define PURPLE 1
#define BLUE   2

int webby = BLUE;   // webby == 2; probably not what was desired

用enum class取代enum

Example, bad

void Print_color(int color);

enum Web_color { red = 0xFF0000, green = 0x00FF00, blue = 0x0000FF };
enum Product_info { Red = 0, Purple = 1, Blue = 2 };

Web_color webby = Web_color::blue;

// Clearly at least one of these calls is buggy.
Print_color(webby);
Print_color(Product_info::Blue);
Print_color(0);

Example, good

void Print_color(Web_color color);

enum class Web_color { red = 0xFF0000, green = 0x00FF00, blue = 0x0000FF };
enum class Product_info { red = 0, purple = 1, blue = 2 };

Print_color(Web_color::red);     // GOOD
Print_color(Product_info::Red);  // Error
Print_color(0);                  // Error

Reference

• Effective Modern C++: Item 10: Prefer scoped enums to unscoped enums
• C++ Core Guidelines: Prefer enumerations over macros
• C++ Core Guidelines: Prefer class enums over "plain" enums