c++ - 为枚举结构设置多个属性

Question

我定义了一个像这样的enum结构

class myC {
  enum accessClass {
    none,
    forL,
    forM,
    forA
  };

  typedef accessClass AccessType;
  AccessType aType;
};

myC obj;

问题是我必须只选择一个成员。但是我想选择多个成员。目前如果我写

obj->aType = forL;
obj->aType = forM;

那么后者将取代第一个。

我想为 enum 结构选择多个项目/成员/属性。

我该怎么办？

Answer 1

使用 bitfield .

enum MyEnum {
    A = 1<<0;   // 0x01
    B = 1<<1;   // 0x02
    C = 1<<2;   // 0x04
    D = 1<<3;   // 0x08
    E = 1<<4;   // 0x10
    F = 1<<5;   // 0x20
    ...
}

MyEnum m;

m = A;             // m = 0x01  (Only A is on)

// Set values by ORing them in.
m |= F;            // OR in field F. Now m = 0x21 (A and F are on)

// Set multiple values by ORing them together.
m = (A | C | E);   // m = 0x15  (A, C, and E)

// Clear values by ANDing them out.
m &= ~C;           // AND out field C. m = 0x11  (A and E are on)

// Test values with AND
if (m & A)
    printf("A is set\n");
if (m & B)
    printf("B is set\n");

参见“使用位标志”:http://www.dylanleigh.net/notes/c-cpp-tricks.html