Question

i would like to do some order to my self about the globals.

1. if i write in my .m file

   int ran //is it global? every class can see it ?
   
   @implementation
   @end
   

2. if i am writing in my .h file this:

   int ran //is it global to any other class that include this .h ?
   @interface
   {
   }
   

3. if i am writing in my .h file this:

   extern int ran //is it global to any other class that include this .h ?
   @interface
   {
   }
   

4. if i am writing in my .h file this:

   @interface
   {
   int ran //can every other class that include it can see it ?
   }
   

   AND about the @interface, every thing that in the interface is belong to that class only?
   what about *NSString that in the @interface? is it belong to that class only ?
   can i use it when including this .h? or do i have to make an object of that class to see it ?

What is the best way to put a global variable of a primitive , that only my class will see it and can be use it ?

Answer 1

1. If you write (in any compilation unit == .m file)

   int ran;
   

   Fine, defines a global variable, initialized to zero, symbol visible to the linker.

2. If you write in a header file

   int ran;
   

   That’s a bad idea, since every implementation file (.m) that includes the header would define it’s own instance of the global variable. Linker confusion would arise.

3. If you write in a header file

   extern int ran;
   

   Fine, declares a global variable. Must be defined in one implementation file (.m).

4. If you write in a header file

   @interface Foo : NSObject
   {
       int ran;
   }
   

   That’s ok, too. It declares an Objective-C class with an instance variable ran. The instance variable would be created for and belong to each instance of Foo. The instance variable is @protected (by default) and can thus be accessed directly from any deriving class. This would be bad design, though.

   Nowadays you would not declare instance variables in the @interface of a class but in the @implementation or just @synthesizethem.

If you need a private global variable, define it in you implementation file using:

static int ran;