Program 15.1

[TotalLuck]

Code: (Objective-C)

#import <Foundation/NSObject.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSValue.h>
#import <Foundation/NSString.h>

int main(int argc, char *argv[])
{
	NSAutoreleasePool * pool = [[NSAutoreleasePool alloc ] init];
	NSNumber	* myNumber , *floatNumber, *intNumber;
	NSInteger	           myInt;
	
	//integer value
	
	intNumber = [NSNumber numberWithInt:100];
	myInt = [intNumber integerValue];
	NSLog(@"%li", (long) myInt);
	
	// long int
	
	myNumber = [NSNumber numberWithLong:0xabcdef];
	NSLog(@"%lx",[myNumber longValue]);
	
	//char value
	
	myNumber = [NSNumber numberWithChar: 'X'];
	NSLog(@"%c", [myNumber charValue]);
	
	// float value
	
	floatNumber = [NSNumber numberWithFloat: 100.00];
	NSLog(@"%g", [floatNumber floatValue]);
	
	//double
	
	myNumber = [NSNumber numberWithDouble: 12345e+15];
	NSLog(@"%lg", [myNumber doubleValue]);
	
	//wrong access here
	
	NSLog(@"%i", [myNumber integerValue]);
	
	//test two numbers
	
	if ([intNumber isEqualToNumber:floatNumber] == YES)
		NSLog(@"Numbers are equal");
	else
		NSLog(@"Numbers are not equal");
	
	//test if one number is  < , ==, or > second num
	
	if ([intNumber compare:myNumber] == NSOrderedAscending)
		NSLog(@"First number is less than second");
	else 
		NSLog(@"first number is not less than second");

[pool drain];
return 0;
}

[/pre]

Program 15.1 output

Code: (Objective-C)

100
abcdef
x
100
1.2345e+19
0
Numbers are equal
First number is less than second

[/pre]

[djeans]

Having a hard time understanding the following code.

Code: (Objective-C)

  intNumber = [NSNumber numberWithInt:100];  
    myInt = [intNumber integerValue];  
    NSLog(@"%li", (long) myInt);  

Can anyone explain why this code

Code: (Objective-C)

NSLog(@"%i", [myNumber integerValue]);  

doesn't work? Or why this does?

Code: (Objective-C)

  NSLog(@"%lx",[myNumber longValue]); 

why does it work for longValue, but not for integerValue?

Thanks

Darron

[skochan]

Note that integerValue returns an NSinteger.  See the discussion of NSInteger on page 324.  It may either be a 32-bit or 64-bit value depending on the compiler options/system architecture.   The safest thing to do is to cast the value to a long as discussed on the page to prevent any assumptions about the size of that data type.

Cheers,

Steve Kochan

[Dorien]

So instead of using:
intNumber = [NSNumber numberWithInt: 100];  // create an object from an integer with a value of 100
NSLog(@"%i", [intNumber integerValue];  // retrieve and display the value

The following is used instead:
intNumber = [NSNumber numberWithInt: 100];   // creates an object from an integer with a value of 100
myInt = [intNumber integerValue];   // retrieves the value of 100 and stores it in myInt
NSLog(@"%li", (long) myInt);  // the qualifier long is used so the value is properly passed and displayed no matter the system architecture

Have I got this right?

On a related note, table 15.1 lists numberWithInteger and numberWithInt.  Are these the same methods?  I ask because numberWithInteger is not listed in my NSNumber Foundation Reference Library.

[skochan]

Yeah, it's in the documentation.  Look here: http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSNumber_Class/Reference/Reference.html#//apple_ref/occ/clm/NSNumber/numberWithInteger:

If you create an integer using numberWithInt:, you should retrieve its value using intValue, and it can be displayed as an int using %i.

If you create an integer using numberWithInteger:, you should retrieve its value using integerValue, and it should be cast as a long if being passed to NSLog to be displayed using %li.   The cast is needed since the number may be a 32 or 64 bit value based upon the build options for the application and the casting guarantees a 64-bit value will be passed to NSLog to be displayed.

Cheers,

Steve

[Dorien]

Thanks for the link and the explanation.  Both were very helpful.

[dharma]

Sorry to revive this thread, but basically we need the intermediate typedef'ed variable myInt, *just* to be able to cast it as a long later on for the NSLog call, right? Just for making working with integers architecture-independent I guess?

So, why would you ever want to use numberWithInt?

Edit: so in the first post the code

Code: (Objective-C)

intNumber = [NSNumber numberWithInt:100];

should be

Code: (Objective-C)

intNumber = [NSNumber numberWithInteger:100];

right?

[skochan]

Yes, that's a good catch!

The intermediate variable is not needed, just used for the sake of example.  You could write this sequence:

Code: (Objective-C)

NSNumber *intNumber = [NSNumber numberWithInteger: 100];    

NSLog(@"%li", (long) [intNumber integerValue]);  

thus avoiding the intermediate variable assignment.

Cheers,

Steve

[dharma]

Thanks for your reply Steve!

By the way, I know others have said it before, but it is *so* cool to have this forum associated with the book and have the writer (you!) actually answering things in person! I'm not aware of any other writer doing such a thing, but I do know some books that certainly could use it Thanks so much for doing this, it really helps me getting more of a grip on Objective-C, it's very reassuring to be able to look things up, seeing other people's solutions, and your suggestions.

[skochan]

You're welcome!   

Steve