- Default value of variables at the time of declaration -

Question

Hey guys,

I was wondering what was the default values of variables before I intialize them ..

For example, if I do :

//myClass.h

BOOL myBOOL; // default value ?
NSArray *myArray; // default value ?
NSUInteger myInteger; // default value ?

Some more examples here :

//myClass.m
// myArray is not initialized, only declared in .h file

if ([myArray count] == 0) { // TRUE or FALSE ?

// do whatever

}

More generally, what is returned when I do :

[myObjectOnlyDeclaredAndNotInitialized myCustomFunction];

Thank you for your answers.

Gotye.

Answer 1

Hi, gotye

by default NSArray value will be nil , if you would not initialize it.

Answer 2

//myClass.h

BOOL myBOOL; // default value ?
NSArray *myArray; // default value ?
NSUInteger myInteger; // default value ?

the Bool myBool if not initialized will receive the default value of False.

NSArray *myArray if not allocated,initialized(for example NSArray *myArray = [[NSArray alloc] init];) will have the default value of NIL. if you call count on an unitialized array you will receive an exception not 0.

//myClass.m
// myArray is not initialized, only declared in .h file

if ([myArray count] == 0) { => here it should crash because of [myArray count]

// do whatever

}

for the NSUInteger myInteger the default value should be 0, the documentation says that this is used to describe an unsigned integer(i didn;t represent integers with this one though)

when you call [myObjectOnlyDeclaredAndNotInitialized myCustomFunction]; it should break, throw an exception.

hope it helps

Answer 3

The answer is that it depends on the scope in which the variable is defined.

Instance variables of Objective-C objects are always initialised to 0/nil/false because the memory allocated is zeroed.

Global variables are probably initialised to 0/nil/false to because when memory is first allocated to a process, it is also zeroed by the operating system. However, as a matter of course, I never rely on that and always initialise them myself.

Local variables are uninitialised and will contain random data depending on how the stack has grown/shrunk.

NB for pointers to Objective-C objects, you can safely send messages to nil. So, for instance:

NSArray* foo = nil;
NSLog(@"%@ count = %d", foo, [foo count]);

is perfectly legal and will run without crashing with output something like:

2010-04-14 11:54:15.226 foo[17980:a0f] (null) count = 0