使用位操作設置某些標誌的最佳做法

Question

我想打開/關閉表示難度級別的3顆星。我不想使用幾個條件，是否可以通過按位操作來實現？

比方說，我已經宣佈這樣一個枚舉：

enum 
{ 
    EASY = 0, 
    MODERATE, 
    CHALLENGING 
} Difficulty; 

我想找到一個位的操作，讓我找到了打開哪個明星或關閉：

如：

level 2 (challenging) 
star 0 -> 1 
star 1 -> 1 
star 2 -> 1 

level 1 (moderate) 
star 0 -> 1 
star 1 -> 1 
star 2 -> 0 

level 0 (easy) 
star 0 -> 1 
star 1 -> 0 
star 2 -> 0 

Answer 1

你會想要做這樣的事情：

typedef enum Difficulty : NSUInteger 
{ 
    EASY = 1 << 0, 
    MODERATE = 1 << 1, 
    CHALLENGING = 1 << 2 
} Difficulty; 

然後檢查一下：

- (void) setStarsWithDifficulty:(Difficulty)diff 
{ 
    star0 = (diff & (EASY | MODERATE | CHALLENGING)); 
    star1 = (diff & (MODERATE | CHALLENGING)); 
    star2 = (diff & CHALLENGING); 
} 

Answer 2

你說的是一樣的東西：

star0 = 1 
star1 = value & CHALLENGING || value & MODERATE 
star2 = value & CHALLENGING 

Answer 3

在這種情況下，如果你想擁有3位，以節省您的星州，如代替有三個布爾標誌，不是你應該做的：

typedef enum 
{ 
    DifficultyEasy = 1 << 0, 
    DifficultyModerate = 1 << 1, 
    DifficultyChallenging = 1 << 2 
} Difficulty; 

Difficulty state = 0; // default 

要設置簡單：

state |= DifficultyEasy; 

要增加挑戰：

state |= DifficultyChallenging; 

要重置很簡單：

state &= ~DifficultyEasy; 

要知道是具有挑戰性的集：

BOOL isChallenging = DifficultyChallenging & state; 

在這種情況下有人需要它是如何工作的解釋：

1 << x means set x bit to 1 (from right); 
// actually it means move 0b00000001 left by x, but I said 'set' to simplify it 

1 << 5 = 0b00100000; 1 << 2 = 0b00000100; 1 << 0 = 0b00000001; 

0b00001111 | 0b11000011 = 0b11001111 (0 | 0 = 0, 1 | 0 = 1, 1 | 1 = 1) 

0b00001111 & 0b11000011 = 0b00000011 (0 & 0 = 0, 1 & 0 = 0, 1 & 1 = 1) 

~0b00001111 = 0b11110000 (~0 = 1, ~1 = 0) 

Answer 4

#define STAR0 1 
#define STAR1 2 
#define STAR2 4 

#define EASY STAR0 
#define MODERATE STAR1|STAR0 
#define CHALLENGING STAR0|STAR1|STAR2 

檢測值d與和和比較反對：0將產生所需的映射，上述的一些樣品給你映射的值來代替，一起來看看：

int d = EASY; 
    NSLog(@"Star 0 %d",(d&STAR0)!=0); 
    NSLog(@"Star 1 %d",(d&STAR1)!=0); 
    NSLog(@"Star 2 %d",(d&STAR2)!=0); 
    d=MODERATE; 
    NSLog(@"Star 0 %d",(d&STAR0)!=0); 
    NSLog(@"Star 1 %d",(d&STAR1)!=0); 
    NSLog(@"Star 2 %d",(d&STAR2)!=0); 
    d=CHALLENGING; 
    NSLog(@"Star 0 %d",(d&STAR0)!=0); 
    NSLog(@"Star 1 %d",(d&STAR1)!=0); 
    NSLog(@"Star 2 %d",(d&STAR2)!=0);