From the definition in objc.h
:
#if (TARGET_OS_IPHONE && __LP64__) || TARGET_OS_WATCH
typedef bool BOOL;
#else
typedef signed char BOOL;
// BOOL is explicitly signed so @encode(BOOL) == "c" rather than "C"
// even if -funsigned-char is used.
#endif
#define YES ((BOOL)1)
#define NO ((BOOL)0)
So, yes, you can assume that BOOL is a char. You can use the (C99) bool
type, but all of Apple’s Objective-C frameworks and most Objective-C/Cocoa code uses BOOL, so you’ll save yourself headache if the typedef ever changes by just using BOOL.