Create an array of integers property in Objective-C

Question

I m having troubles creating a property of an array of integers in Objective-C  I m not sure whether this is even possible to do in Obj-C so I m hoping someone can help me in finding out either how to do it correctly or provide an alternative solution   myclass h   interface myClass   NSObject     private int doubleDigits 10       property int doubleDigits   end   myclass m   implementation myClass       synthesize doubleDigits      - id  init            self    super init            int doubleDigits 10     1 2 3 4 5 6 7 8 9 10            return self              end   When I build and run  I get the following error      error  type of property  doubleDigits    does not match type of ivar    doubleDigits

User · Answer

I found all the previous answers too much complicated. I had the need to store an array of some ints as a property, and found the ObjC requirement of using a NSArray an unneeded complication of my software.

So I used this:

typedef struct my10ints {
    int arr[10];
} my10ints;

@interface myClasss : NSObject

@property my10ints doubleDigits;

@end

This compiles cleanly using Xcode 6.2.

My intention was to use it like this:

myClass obj;
obj.doubleDigits.arr[0] = 4;

HOWEVER, this does not work. This is what it produces:

int i = 4;
myClass obj;
obj.doubleDigits.arr[0] = i;
i = obj.doubleDigits.arr[0];
// i is now 0 !!!

The only way to use this correctly is:

int i = 4;
myClass obj;
my10ints ints;
ints = obj.doubleDigits;
ints.arr[0] = i;
obj.doubleDigits = ints;
i = obj.doubleDigits.arr[0];
// i is now 4

and so, defeats completely my point (avoiding the complication of using a NSArray).

User · Answer

You can put this in your  h file for your class and define it as property  in XCode 7      property int    stuffILike   10

User · Answer

You can put this in your  h file for your class and define it as property  in XCode 7      property int    stuffILike   10

User · Answer

C arrays are not one of the supported data types for properties  See  The Objective-C Programming Language  in Xcode documentation  in the Declared Properties page      Supported Types       You can declare a property for any   Objective-C class  Core Foundation   data type  or    plain old data     POD    type  see C   Language Note  POD   Types   For constraints on using Core   Foundation types  however  see    Core   Foundation       POD does not include C arrays  See  http   www fnal gov docs working-groups fpcltf Pkg ISOcxx doc POD html  If you need an array  you should use NSArray or NSData    The workarounds  as I see it  are like using  void    to circumvent type checking  You can do it  but it makes your code less maintainable

User · Answer

This should work    interface MyClass       int  doubleDigits 10        property readonly  int  doubleDigits    end   implementation MyClass  -  int   doubleDigits       return  doubleDigits      end

User · Answer

I m just speculating   I think that the variable defined in the ivars allocates the space right in the object  This prevents you from creating accessors because you can t give an array by value to a function but only through a pointer  Therefore you have to use a pointer in the ivars   int  doubleDigits    And then allocate the space for it in the init-method    synthesize doubleDigits   -  id init       if  self    super init             doubleDigits   malloc sizeof int    10                         This works  but is dangerous  forbidden  because bufferDoubleDigits            gets deleted at the end of - id init because it s on the stack             int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10               self setDoubleDigits bufferDoubleDigits                         If you want to be on the safe side use memcpy    needs  include  lt string h gt              doubleDigits   malloc sizeof int    10              int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10              memcpy doubleDigits  bufferDoubleDigits  sizeof int    10                         return self     -  void dealloc       free doubleDigits        super dealloc       In this case the interface looks like this    interface MyClass   NSObject       int  doubleDigits     property int  doubleDigits    Edit   I m really unsure wether it s allowed to do this  are those values really on the stack or are they stored somewhere else  They are probably stored on the stack and therefore not safe to use in this context   See the question on initializer lists   int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10    self setDoubleDigits bufferDoubleDigits

User · Answer

This works    interface RGBComponents   NSObject        float components 8        property readonly  float   components      -  float    components       return components

User · Answer

This should work    interface MyClass       int  doubleDigits 10        property readonly  int  doubleDigits    end   implementation MyClass  -  int   doubleDigits       return  doubleDigits      end

User · Answer

Like lucius said  it s not possible to have a C array property  Using an NSArray is the way to go  An array only stores objects  so you d have to use NSNumbers to store your ints  With the new literal syntax  initialising it is very easy and straight-forward   NSArray  doubleDigits       1   2   3   4   5   6   7   8   9   10      Or   NSMutableArray  doubleDigits    NSMutableArray array    for  int n   1  n  lt   10  n         doubleDigits addObject   n      For more information  NSArray Class Reference  NSNumber Class Reference  Literal Syntax

User · Answer

This should work    interface MyClass       int  doubleDigits 10        property readonly  int  doubleDigits    end   implementation MyClass  -  int   doubleDigits       return  doubleDigits      end

User · Answer

Like lucius said  it s not possible to have a C array property  Using an NSArray is the way to go  An array only stores objects  so you d have to use NSNumbers to store your ints  With the new literal syntax  initialising it is very easy and straight-forward   NSArray  doubleDigits       1   2   3   4   5   6   7   8   9   10      Or   NSMutableArray  doubleDigits    NSMutableArray array    for  int n   1  n  lt   10  n         doubleDigits addObject   n      For more information  NSArray Class Reference  NSNumber Class Reference  Literal Syntax

User · Answer

I found all the previous answers too much complicated. I had the need to store an array of some ints as a property, and found the ObjC requirement of using a NSArray an unneeded complication of my software.

So I used this:

typedef struct my10ints {
    int arr[10];
} my10ints;

@interface myClasss : NSObject

@property my10ints doubleDigits;

@end

This compiles cleanly using Xcode 6.2.

My intention was to use it like this:

myClass obj;
obj.doubleDigits.arr[0] = 4;

HOWEVER, this does not work. This is what it produces:

int i = 4;
myClass obj;
obj.doubleDigits.arr[0] = i;
i = obj.doubleDigits.arr[0];
// i is now 0 !!!

The only way to use this correctly is:

int i = 4;
myClass obj;
my10ints ints;
ints = obj.doubleDigits;
ints.arr[0] = i;
obj.doubleDigits = ints;
i = obj.doubleDigits.arr[0];
// i is now 4

and so, defeats completely my point (avoiding the complication of using a NSArray).

User · Answer

I m just speculating   I think that the variable defined in the ivars allocates the space right in the object  This prevents you from creating accessors because you can t give an array by value to a function but only through a pointer  Therefore you have to use a pointer in the ivars   int  doubleDigits    And then allocate the space for it in the init-method    synthesize doubleDigits   -  id init       if  self    super init             doubleDigits   malloc sizeof int    10                         This works  but is dangerous  forbidden  because bufferDoubleDigits            gets deleted at the end of - id init because it s on the stack             int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10               self setDoubleDigits bufferDoubleDigits                         If you want to be on the safe side use memcpy    needs  include  lt string h gt              doubleDigits   malloc sizeof int    10              int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10              memcpy doubleDigits  bufferDoubleDigits  sizeof int    10                         return self     -  void dealloc       free doubleDigits        super dealloc       In this case the interface looks like this    interface MyClass   NSObject       int  doubleDigits     property int  doubleDigits    Edit   I m really unsure wether it s allowed to do this  are those values really on the stack or are they stored somewhere else  They are probably stored on the stack and therefore not safe to use in this context   See the question on initializer lists   int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10    self setDoubleDigits bufferDoubleDigits

User · Answer

C arrays are not one of the supported data types for properties  See  The Objective-C Programming Language  in Xcode documentation  in the Declared Properties page      Supported Types       You can declare a property for any   Objective-C class  Core Foundation   data type  or    plain old data     POD    type  see C   Language Note  POD   Types   For constraints on using Core   Foundation types  however  see    Core   Foundation       POD does not include C arrays  See  http   www fnal gov docs working-groups fpcltf Pkg ISOcxx doc POD html  If you need an array  you should use NSArray or NSData    The workarounds  as I see it  are like using  void    to circumvent type checking  You can do it  but it makes your code less maintainable

User · Answer

I m just speculating   I think that the variable defined in the ivars allocates the space right in the object  This prevents you from creating accessors because you can t give an array by value to a function but only through a pointer  Therefore you have to use a pointer in the ivars   int  doubleDigits    And then allocate the space for it in the init-method    synthesize doubleDigits   -  id init       if  self    super init             doubleDigits   malloc sizeof int    10                         This works  but is dangerous  forbidden  because bufferDoubleDigits            gets deleted at the end of - id init because it s on the stack             int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10               self setDoubleDigits bufferDoubleDigits                         If you want to be on the safe side use memcpy    needs  include  lt string h gt              doubleDigits   malloc sizeof int    10              int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10              memcpy doubleDigits  bufferDoubleDigits  sizeof int    10                         return self     -  void dealloc       free doubleDigits        super dealloc       In this case the interface looks like this    interface MyClass   NSObject       int  doubleDigits     property int  doubleDigits    Edit   I m really unsure wether it s allowed to do this  are those values really on the stack or are they stored somewhere else  They are probably stored on the stack and therefore not safe to use in this context   See the question on initializer lists   int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10    self setDoubleDigits bufferDoubleDigits

User · Answer

I m just speculating   I think that the variable defined in the ivars allocates the space right in the object  This prevents you from creating accessors because you can t give an array by value to a function but only through a pointer  Therefore you have to use a pointer in the ivars   int  doubleDigits    And then allocate the space for it in the init-method    synthesize doubleDigits   -  id init       if  self    super init             doubleDigits   malloc sizeof int    10                         This works  but is dangerous  forbidden  because bufferDoubleDigits            gets deleted at the end of - id init because it s on the stack             int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10               self setDoubleDigits bufferDoubleDigits                         If you want to be on the safe side use memcpy    needs  include  lt string h gt              doubleDigits   malloc sizeof int    10              int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10              memcpy doubleDigits  bufferDoubleDigits  sizeof int    10                         return self     -  void dealloc       free doubleDigits        super dealloc       In this case the interface looks like this    interface MyClass   NSObject       int  doubleDigits     property int  doubleDigits    Edit   I m really unsure wether it s allowed to do this  are those values really on the stack or are they stored somewhere else  They are probably stored on the stack and therefore not safe to use in this context   See the question on initializer lists   int bufferDoubleDigits      1 2 3 4 5 6 7 8 9 10    self setDoubleDigits bufferDoubleDigits

User · Answer

This should work    interface MyClass       int  doubleDigits 10        property readonly  int  doubleDigits    end   implementation MyClass  -  int   doubleDigits       return  doubleDigits      end

User · Answer

This works    interface RGBComponents   NSObject        float components 8        property readonly  float   components      -  float    components       return components

[objective-c] Create an array of integers property in Objective-C

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