OC基础复习02-BOOL

 1 /// Type to represent a boolean value.
 2 #if !defined(OBJC_HIDE_64) && TARGET_OS_IPHONE && __LP64__
 3 typedef bool BOOL;
 4 #else
 5 typedef signed char BOOL; 
 6 // BOOL is explicitly signed so @encode(BOOL) == "c" rather than "C" 
 7 // even if -funsigned-char is used.
 8 #endif
 9 
10 #if __has_feature(objc_bool)
11 #define YES __objc_yes
12 #define NO  __objc_no
13 #else
14 #define YES ((BOOL)1)
15 #define NO  ((BOOL)0)
16 #endif