Question

Possible Duplicate:
What values should I use for iOS boolean states?

I believe there are something like 5 boolean types in iOS environment (which comes from C, C++ and Objective C).

• _Bool
• bool
• BOOL
• boolean_t
• Boolean

And there are at least four pairs of values for them:

• true, false
• TRUE, FALSE
• YES, NO
• 1, 0

Which one do you think is the best (style wise) to use for iOS Objective C development?

Update 1

I mentioned a type “boolean”. It looks like it doesn’t exist. I removed it from the list and added _Bool.

I am aware of typedef’s for these types and values. The question is about style differences.

Answer 1

iOS and OS X are mostly made of Cocoa, which use the boolean type BOOL with values YES/NO.

bool

• Defined by C++.
• A true boolean, guaranteed to be 0 or 1.

_Bool

• Defined by C99.
• A true boolean, guaranteed to be 0 or 1.
• If stdbool.h is included, bool is #defined as _Bool.

BOOL

• Defined by the Objective-C runtime at /usr/include/objc/objc.h.
• A signed char in 32 bit. Values may be YES (0x01), NO (0x00), or anything in the range -127 to 128. YES/NO are defined at <Foundation/NSObjCRuntime.h>.
• A bool in 64 bits, guaranteed to be 0 or 1.

Boolean

• Defined by Carbon at CFBase.h.
• An unsigned char.
• Values may be TRUE (0x01), FALSE (0x00), or anything in the range -127 to 128.

boolean_t

• Defined by /usr/include/mach/i386/boolean.h
• An int in x32 or unsigned int in x64.

For non true boolean types:

• Any non zero value is treated as true in logical expressions.
• If you cast to a boolean types with less range than the casted type, only the lower bytes are used.

---

Cases where one type or another makes a difference are hard to imagine. There are several cases where casting to BOOL may bite you, and some rare situations (eg: KVO converts BOOL to a NSNumber, and bool to a CFBoolean). If anything, when you consistently use BOOL, you are covered in case Apple changes its definition.