Consider the following NSNumber instances:
NSNumber *b1 = #((long)(-61));
NSNumber *b2 = #((long)(-62));
NSLog(#"%#", b1);
NSLog(#"%#", b2);
The “Variables View” within the “Debug Area” shows curious values:
Does someone has any idea about this debugger infomation?
0xffffffffffffffc3 is the hex representation of -61.
0x00ffffffffffffc3 is the hex representation of 72057594037927875.
The “Variables View” within the “Debug Area” simply has troubles correctly representing negative long values of a NSNumber.
What’s ironic is that if you use an unsigned long for the underlying value for the NSNumber (see value4/b4 in above screen snapshot), the variables view will now show it as -61.
But, this is just a bug in the display of the NSNumber instances in the “Variables View”. The actual NSNumber values are fine.
Related
I'm creating a random number and storing it in a NSNumber object like this:
NSNumber *index = [NSNumber numberWithUnsignedInt:arc4random_uniform(2^32-1)];
I also tried:
NSNumber *index = [NSNumber numberWithUnsignedInt:arc4random_uniform(4294967295)];
NSNumber *index = #(arc4random_uniform(4294967295));
At some point I'm also assigning the number 1 like this:
NSNumber *index = #(1);
This should give me only positive numbers.
Later on, I print out these numbers like this:
NSString *string = [NSString stringWithFormat:#"%#", index];
This gives me some negative values for the random numbers and 1 is being printed as 1. So I though maybe if I do:
NSString *string = [NSString stringWithFormat:#"%u", index.unsignedIntValue];
I'll get only positive numbers - which I do - but now 1 is suddenly being printed as some large positive number, also.
What's going on here? How can I correctly store a u_int32 (which arc4random returns) in a NSNmber and make sure that they are only positive?
Use
NSNumber *index = [NSNumber numberWithUnsignedInt:arc4random_uniform(exp2(32)-1)];
I never get any negative numbers. arc4random_uniform(x) always returns a number between 0 and x, and the stringvalue of the NSNumber generated from it is correct.
EDIT: replaced exp2(31) with exp2(32)
You said in a comment that the index is stored in a Core Data entity as an "Integer 32" attribute, and I assume that is where the problem comes from.
Core Data dynamically generates getter and setter methods for all attributes (and relationships) of managed object classes. These accessor methods are different from the "usual" #synthesized accessor methods which are backed up by an instance variable.
For an "Integer 32" attribute, Core Data uses a (signed) integer for the attribute, and when you set a value, it is just cast or truncated to int. Example:
e.index = [NSNumber numberWithUnsignedInt:0xFFFFFFF0U];
// This would give the same result:
// e.index = [NSNumber numberWithLongLong:0x1234FFFFFFF0LL];
NSNumber *val = e.index;
NSLog(#"value=%#, type=%s", val, [val objCType]);
// Output: value=-16, type=i
The output type=i shows that the value contains an int.
If you need unsigned integers in the range 0 .. 2^32-1, then you can either (as you already did) use unsignedIntValue:
unsigned x = [val unsignedIntValue];
or store the attribute as "Integer 64".
Remarks:
I am fairly sure that this is not a problem of arc4random_uniform.
In your first code example arc4random_uniform(2^32-1), you should note that ^ is exclusive-or, not exponentiation.
I am trying to grab the value of an NSInteger and set a UILabel value to it. The code is as follows:
counter_.text = [NSString stringWithFormat:#"%#", [counterAmount intValue]];
where counter_ is my label and counterAmount is my NSInteger. I keep getting a "Receiver type 'NSInteger *' (aka 'int *') is not 'id' or interface pointer, consider casting it to id.
I'm not quite sure how to understand this. I appreciate of your help.
intValue is an NSNumber method that returns a C primitive value. %# prints objects. In order to output a C primitive value you have to supply the type in the formatting string. %d is the type for signed integer.
As per the question, and as pointed out to me quite correctly by borrden below, the type being dealt with here is NSInteger rather than NSNumber. In iOS NSInteger is a typedef of int, so you're dealing directly with a primitive type. The NS prefix does not mean that its an object.
Since counterAmount is a NSInteger, you can not use intValue on it (since it isn't an object, you can't send any messages to it, actually).
Instead, use:
counter_.text = [NSString stringWithFormat:#"%d", counterAmount];
Now that being said, if you are displaying this value to a user you should really be using a number formatter so that it is formatted the way that they have set it up to display in the settings app:
NSNumber *number = [NSNumber numberWithInt:counterAmount];
NSNumberFormatter *formatter = [NSNumberFormatter new];
formatter.numberStyle = NSNumberFormatterDecimalStyle; // Or whichever style is appropriate for your number.
counter_.text = [formatter stringFromNumber:number];
this is the code:
NSNumber *taskId = [[self.taskList objectAtIndex:indexPath.row] valueForKey:#"identity"];
NSInteger *intTaskId = [[self.taskList objectAtIndex:indexPath.row] valueForKey:#"identity"];
self.taskList is an NSArray which filled with core data fetch request in ViewController's viewDidLoad method.
the taskId is: 1
the intTaskId is: 269303816
In actually, the value stored in core data is: 1
below is my questions:
1, I am confused why the NSInteger incorrect?
2, Should I have to replace NSInteger with NSNumber to avoid any other problems?
NSNumber is an object, whereas NSInteger is simply a typedef for a primitive (non-object) type (like int). NSInteger is not a subclass of NSNumber. Core Data returns numbers as instances of NSNumber. You're getting the weird NSInteger value because it's pointing to an object of type NSNumber but attempting to print it as if it were just an integer.
You'll need to replace NSInteger with NSNumber to avoid any problems. You could also use the intValue method on NSNumber to get back an NSInteger:
NSNumber *objTaskId = [[self.taskList objectAtIndex:indexPath.row] valueForKey:#"identity"];
NSInteger *intTaskId = [objTaskId intValue];
You'll need to do this if you want to do comparisons (greater than, equal too, smaller than) or arithmetic (you can't add an NSNumber to another NSNumber or an NSNumber to a primitive type like an int or float).
I'm getting the ID of a media item from the MPMediaPickerController. According to the documentation, this value is an NSNumber object containing a uint64_t (unsigned long long). I would like to convert it to an NSString for saving in my data model. However, when I convert it to a string its value changes, and when I convert it back to a number it changes again! Obviously I'm not understanding something about these data types. Can you help?
MPMediaItem *mediaPicked;
// set mediaPicked to an MPMedia item using MPMediaPickerController...
NSLog(#"id as number: %qu", [mediaPicked valueForProperty:MPMediaItemPropertyPersistentID]); // outputs 566042331449280
NSLog(#"id as string: %#", [[mediaPicked valueForProperty:MPMediaItemPropertyPersistentID] stringValue]); // outputs 16204893883745507648
NSLog(#"id as number: %qu", [[[mediaPicked valueForProperty:MPMediaItemPropertyPersistentID] stringValue] longLongValue]); // outputs 9223372036854775807
If I try to play the media item before this conversion, it always works. But if I try to play the media item after this conversion, only about half of the media items I've tried work. So some ID values survive the conversion and some don't.
You are starting by saying this:
NSLog(#"id as number: %qu", [mediaPicked valueForProperty:MPMediaItemPropertyPersistentID]); // outputs 566042331449280
But that's wrong. %qu means "this thing is an unsigned long long". But this thing is not an unsigned long long. It's an object! It's an NSNumber wrapped around an unsigned long long. You are lying to NSLog, so you're getting garbage output in your very first statement.
Now, try this on your own machine:
uint64_t x = 16204893883745507648ULL;
NSLog(#"%qu", x);
NSNumber* n = [NSNumber numberWithUnsignedLongLong:x];
NSLog(#"%#", n);
NSLog(#"%#", [n stringValue]);
All of those NSLog statements give the same result - because they are all correct formulations, unlike the one you started with. So, those NSLog statements show you the kind of thing you ought to be saying.
Now, you might think: Oh, great, so I can get from an NSNumber to an NSString with stringValue after all. Yes, but you can't get back again. We cannot get from [n stringValue] to a correct NSNumber by using longlongValue, because a long long is not an unsigned long long. There is no unsignedLonglongValue. So you can't get there from here.
So what's the right thing to do? Don't convert at all! You've got an NSNumber, it's valid, just keep it and use it. An NSNumber is a value you can store in your model. (For example, it can go into a dictionary as a value or as a key, it can be a value in user defaults, and so on.)
I am trying to parse a json value to a decimal with no success. I am using the following framework
http://code.google.com/p/json-framework/
and my code is as follows
NSDecimal RRP = [[jProduct objectForKey:#"Price"] decimalValue];
NSLog(#"%#", RRP);
I get
Program received signal: “EXC_BAD_ACCESS”.
Just to test I thought I would try this:
NSLog(#"%#", [jProduct objectForKey:#"Price"]);
42.545
I get the value but obviously I have not set the NSDecimal.
Anybody else had similar experince or can see what I am doing wrong?
Thanks
I'm not familiar with the framework you are using but I would suggest the following:
What is the type returned by [jProduct objectForKey:#"price"]?
You probably need to work around the fact that this is the wrong type - maybe a an NSString?
Try:
NSDecimal RRP = [[NSDecimalNumber decimalNumberWithString:[jProduct objectForKey:#"Price"] decimalValue];
Edit:
Oh and NSDecimal is a struct, not an object so you shouldn't be using NSLog(#"%#"); as the %# format identifier is for objects.. Instead you can use the basic type format identifiers such as %d or %i and access the components of the structure individually.
However, as you probably want to log a decimal rather than the components of the struct (sign, mantissa etc) then you will probably want to convert it back to an NSDecimalNumber (which is an object).
So it becomes:
NSLog(#"%#", [NSDecimalNumber decimalNumberWithDecimal:RRP]);
[jProduct objectForKey:#"Price"]
may be a NSString. NSString respond to:
– doubleValue
– floatValue
– intValue
– integerValue
– longLongValue
– boolValue
not decimalValue
Verify the class of your data.
store the value in NSNumber
NSNumber *num = [jProduct objectForKey:#"Price"];
An NSDecimal is a struct, not an object. If you want to print an NSDecimal, use NSDecimalString():
NSDecimal rrp = [[jProduct objectForKey:#"Price"] decimalValue];
NSLog(#"%#", NSDecimalString(rrp));
See Decimal & JSON example. I think it will help you.