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All types of booleans in ObjectiveC

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

I believe there are something like 5 boolean types in the iOS environment (which come 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
  • WELL NO
  • ten

What do you think is the best (style wise) for iOS Objective C development?

Update 1

I mentioned the "boolean" type. It looks like it's not there. I removed it from the list and added _Bool.

I am aware of the typedef for these types and values. It's about style differences.

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6 answers


iOS and OS X are mostly composed of Cocoa, which use a boolean type BOOL

with values YES

/ NO

.

<L> <Dt> dt> <Dd>    BOOL

  •     
  • Defined by C ++.    
  • A true boolean value, guaranteed to be 0 or 1.  
Dd> < dt> dt> <dd>    _Bool

  •     
  • Defined by C99.    
  • A true boolean value, guaranteed to be 0 or 1.    
  • If stdbool.h is included, bool #defined as _Bool.  
Dd> < dt> dt> <dd>    BOOL

  •     
  • Defined in the Objective-C framework with /usr/include/objc/objc.h

    .    
  • A signed char

    in 32 bits. Values ​​can be YES

    (0x01), NO

    (0x00), or anything in the range -127 to 128. YES

    / are NO

    defined in <Foundation/NSObjCRuntime.h>

    .    
  • A BOOL

    in 64 bits, guaranteed 0 or 1.  
Dd> <dt> Boolean



dt> <Dd>   
  •     
  • Defined by Carbon at CFBase.h .    
  • Unsigned char.    
  • Values ​​can be TRUE

    (0x01), FALSE

    (0x00), or anything in the range -127 to 128.  
Dd> < dt> dt> <dd>    boolean_t

  •     
  • Defined /usr/include/mach/i386/boolean.h

        
  • int in x32 or unsigned int in x64.  
Dd> dl>

For invalid boolean types:

  • Any non-zero value is considered true in logical expressions.
  • If you are using booleans with a smaller range than the cast type, only the lower bytes are used.

Cases where one type or the other matter is hard to imagine. There are a few cases where casting to BOOL can bite you, as well as some rare situations (for example: KVO converts BOOL to NSNumber and bool to CFBoolean). Anyway, when you use BOOL consistently, you will be considered in case Apple changes its definition.

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Use BOOL

and YES

/ NO

in Objective-C code. This is expected in Objective-C code and how Objective-C headers define the data type. (Note that sometimes you can deal with other types / values, for example, when checking the "truthfulness" of pointers or when working with code, for example in C ++, but Objective-C usually uses BOOL

and YES

/ NO

for types and values ​​boolean data.)



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It is basically totally indifferent. In practice, I'm sure they even announced the same: typedef signed char BOOL;

, typedef signed char Boolean;

etc.

Thus, they are practically compatible and equivalent; however, the best approach is to respect methods like expect and return, so write

[object someObjectiveCMethod:YES];

instead

[object someObjectiveCMethod:TRUE];

and

CFWhateverSetBooleanProperty(true);

instead

CFWhateverSetBooleanProperty(YES);
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Use OBJC BOOL for ObjC code. Use others where they are "native". Anything else will stand out as "unusual" and deserve extra care when reading code, which is a property that should be reserved for code that is actually unusual and deserves special care.

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BOOL with YES and NO.

However, BOOL is signed by char, so YES is 1 and NO is 0.

In objc.h

they are defined as:

typedef signed char BOOL;

AND

#define YES ((BOOL)1)
#define NO  ((BOOL)0)
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You could use everyone if not for the fact that whoever reads the code may not know this type. So for convention, use BOOL

which can be YES

(1) or NO

.

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