Objective-C BOOL vs bool

Question

I saw the  new type  BOOL  YES  NO    I read that this type is almost like a char   For testing I did    NSLog   Size of BOOL  d   sizeof BOOL    NSLog   Size of bool  d   sizeof bool      Good to see that both logs display  1   sometimes in C   bool is an int and its sizeof is 4   So I was just wondering if there were some issues with the bool type or something    Can I just use bool  that seems to work  without losing speed

User · Answer

The Objective-C type you should use is BOOL  There is nothing like a native boolean datatype  therefore to be sure that the code compiles on all compilers use BOOL   It s defined in the Apple-Frameworks

User · Answer

Yup  BOOL is a typedef for a signed char according to objc h   I don t know about bool  though   That s a C   thing  right   If it s defined as a signed char where 1 is YES true and 0 is NO false  then I imagine it doesn t matter which one you use   Since BOOL is part of Objective-C  though  it probably makes more sense to use a BOOL for clarity  other Objective-C developers might be puzzled if they see a bool in use

User · Answer

From the definition in objc h    if  TARGET OS IPHONE  amp  amp    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

User · Answer

I go against convention here  I don t like typedef s to base types  I think it s a useless indirection that removes value    When I see the base type in your source I will instantly understand it  If it s a typedef I have to look it up to see what I m really dealing with  When porting to another compiler or adding another library their set of typedefs may conflict and cause issues that are difficult to debug  I just got done dealing with this in fact  In one library boolean was typedef ed to int  and in mingw gcc it s typedef ed to a char

User · Answer

At the time of writing this is the most recent version of objc h       Type to represent a boolean value   if  TARGET OS IPHONE  amp  amp    LP64         TARGET OS WATCH  define OBJC BOOL IS BOOL 1 typedef bool BOOL   else  define OBJC BOOL IS CHAR 1 typedef signed char BOOL      BOOL is explicitly signed so  encode BOOL      c  rather than  C      even if -funsigned-char is used   endif   It means that on 64-bit iOS devices and on WatchOS BOOL is exactly the same thing as bool while on all other devices  OS X  32-bit iOS  it is signed char and cannot even be overridden by compiler flag -funsigned-char  It also means that this example code will run differently on different platforms  tested it myself    int myValue   256  BOOL myBool   myValue  if  myBool        printf  i m 64-bit iOS      else       printf  i m 32-bit iOS        BTW never assign things like array count to BOOL variable because about 0 4  of possible values will be negative

User · Answer

As mentioned above BOOL could be an unsigned char type depending on your architecture  while bool is of type int  A simple experiment will show the difference why BOOL and bool can behave differently   bool ansicBool   64  if ansicBool    true  printf  This will not print n     printf  Any given vlaue other than 0 to ansicBool is evaluated to  i n   ansicBool    BOOL objcBOOL   64  if objcBOOL    YES  printf  This might print depnding on your architecture n     printf  BOOL will keep whatever value you assign it   i n   objcBOOL    if  objcBOOL  printf  This will not print n     printf    operator will zero objcBOOL  i n    objcBOOL    if   objcBOOL  printf     will evaluate objcBOOL value to  i n     objcBOOL     To your surprise if objcBOOL    YES  will evaluates to 1 by the compiler  since YES is actually the character code 1  and in the eyes of compiler  character code 64 is of course not equal to character code 1 thus the if statement will evaluate to YES true 1 and the following line will run  However since a none zero bool type always evaluates to the integer value of 1  the above issue will not effect your code  Below are some good tips if you want to use the Objective-C BOOL type vs the ANSI C bool type    Always assign the YES or NO value and nothing else  Convert BOOL types by using double not    operator to avoid unexpected results  When checking for YES use if  myBool  instead of if myBool    YES  it is much cleaner to use the not   operator and gives the expected result

User · Answer

Another difference between bool and BOOL is that they do not convert exactly to the same kind of objects  when you do key-value observing  or when you use methods like - NSObject valueForKey     As everybody has said here  BOOL is char  As such  it is converted to an NSNumber holding a char  This object is indistinguishable from an NSNumber created from a regular char like  A  or   0   You have totally lost the information that you originally had a BOOL   However  bool is converted to an CFBoolean  which behaves the same as NSNumber  but which retains the boolean origin of the object   I do not think that this is an argument in a BOOL vs  bool debate  but this may bite you one day   Generally speaking  you should go with BOOL  since this is the type used everywhere in the Cocoa iOS APIs  designed before C99 and its native bool type

User · Answer

The accepted answer has been edited and its explanation become a bit incorrect  Code sample has been refreshed  but the text below stays the same  You cannot assume that BOOL is a char for now since it depends on architecture and platform   Thus  if you run you code at 32bit platform for example iPhone 5  and print  encode BOOL  you will see  c   It corresponds to a char type  But if you run you code at iPhone 5s 64 bit  you will see  B   It corresponds to a bool type

User · Answer

Also  be aware of differences in casting  especially when working with bitmasks  due to casting to signed char   bool a   0x0100  a    true      expression true  BOOL b   0x0100  b    false     expression true on    TARGET OS IPHONE  amp  amp    LP64       TARGET OS WATCH   e g  MacOS b    true      expression true on  TARGET OS IPHONE  amp  amp    LP64       TARGET OS WATCH   If BOOL is a signed char instead of a bool  the cast of 0x0100 to BOOL simply drops the set bit  and the resulting value is 0

User · Answer

As mentioned above  BOOL is a signed char  bool - type from C99 standard  int     BOOL - YES NO  bool - true false    See examples   bool b1   2  if  b1  printf  REAL b1  n    if  b1    true  printf  NOT REAL b1  n     BOOL b2   2  if  b2  printf  REAL b2  n    if  b2    YES  printf  NOT REAL b2  n      And result is     REAL b1   REAL b2   NOT REAL b2   Note that bool    BOOL  Result below is only ONCE AGAIN - REAL b2   b2   b1  if  b2  printf  ONCE AGAIN - REAL b2  n    if  b2    true  printf  ONCE AGAIN - NOT REAL b2  n      If you want to convert bool to BOOL you should use next code  BOOL b22   b1   YES   NO    and back - bool b11   b2   true   false    So  in our case   BOOL b22   b1   2   NO  if  b22     printf  ONCE AGAIN MORE - REAL b22  n    if  b22    YES  printf  ONCE AGAIN MORE- NOT REAL b22  n      And so   what we get now   -

[c] Objective-C : BOOL vs bool

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