How can I solve this problem?
code:
[NSNumber numberWithInteger:[buttonStatsInSection objectAtIndex:row]]
warning: passing argument 1 of 'numberWithInteger:' makes integer from pointer without a cast
Thanks.
numberWithInteger: needs you to give it an int to create the NSNumber. You are giving it an object, because objectAtIndex: returns an object.
Even if the object you have at that row is an NSNumber, or anything else, you still need to get an actual int data type out of it somehow.
For example, if the object you get back is an NSNumber, you could have something like this in the end:
NSNumber * myNSNum = [buttonStatsInSection objectAtIndex:row];
int myInt = [myNSNum intValue];
[NSNumber numberWithInteger:myInt];
Why are you creating a new NSNumber object? Do you really want a copy of it, or do you just want a reference to it? What do you plan to do with it? If you want a copy, you can just do:
NSNumber* copy = (NSNumber*)[[buttonStatsInSection objextAtIndex:row] copy];
Otherwise just do:
NSNumber* num = (NSNumber*)[buttonStatsInSection objextAtIndex:row];
Either way it isn't necessary to go through the process of extracting the int value and the converting it right back to an NSNumber
Related
My question is as it is in the title. However, if it isn't an object, how can it then be maintained in NSMutableArray as an object? Because NSMutableArray is only for storing objects or am I wrong? :)
Primitive types, like int, must be wrapped in an object before it can be added to a collection class like NSMutableArray. Try this:
int nameOfVariable = 42;
NSMutableArray *array = ... // the initialized array
[array addObject:#(nameOfVariable)];
The last line is modern syntax that essentially means:
[array addObject:[NSNumber numberWithInt:nameOfVariable]];
Later on, when you need to get the value back, you do:
int someVariable = [array[someIndex] intValue];
No, it is not an object and you can therefore not put it in an NSArray. You have to wrap it in an NSNumber, which is an object and can be put in an NSArray.
An int is a primitive type inherited from C (examples of other primitive types are char, long, float, etc.). These are not Objective-C objects. To add a primitive type to an NSMutableArray or any other Objective-C collection, you must wrap them in an object. For number types like int, you would use NSNumber as follows:
int i = 1;
[array addObject:#(i)]; // #(i) is equivalent to [NSNumber numberWithInt:i]
I have an NSArray called allQuestions with objects that have a BOOL property called isCorrect
I tried
int res = [self.allQuestions valueForKeyPath:#"#sum.isCorrect"];
but this always gives me a bogus number. I though YES would count as 1, and NO as 0. What am I missing here. Is there no guarantee of the values? If no, what's the best way do achieve this simple thing without iterating over the array?
Edit: just to be precise: I'm interested in the count (number) of elements that evaluate to YES.
int res = [[self.allQuestions valueForKeyPath:#"#sum.isCorrect"] intValue];
valueForKeyPath returns NSNumber's object. You need convert it in to primitive type int or use pointer at NSNumber.
You should wrap the booleans in NSNumber when adding to an array:
BOOL b = YES;
[self.allQuestions addObject:[NSNumber numberWithBool:b]];
And retrieve in the same way:
BOOL b = [[self.allQuestions valueForKeyPath:#"#sum.isCorrect"] boolValue];
Solved:
NSNumber * res = [self.allQuestions valueForKeyPath:#"#sum.isCorrect"];
It returns an NSNumber, of course...
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 got a NSMutableArray object with int values
and I can get a certain value via :
int *v0=[[[arrayObj objectAtIndex:0] intValue];
there is no problem.
But
I got a NSMutableArray object with NSString values
and I cannot get a certain value via :
NSString *v0=[[[arrayObj objectAtIndex:0] stringValue];
//raises error
I want to learn and understand exactly what stringValue for... and why this error occurs ?
NSString *v0=[arrayObj objectAtIndex:0];
works as expected.I asusme its some kind of pointer with null terminated so it can leech value.
Im not sure this line is also unicode/encoded string safe code.
in conclusion:
want to know the purpose of stringValue with some lines o code snippets
I got a NSMutableArray object with int values
That's not possible, Cocoa arrays always contain objects. You probably have an array of NSNumber objects that wrap the integers, like:
NSArray *arrayOfNumbers = #[#1, #2, #3];
NSNumber objects have an intValue method, so this works:
int value = [arrayOfNumbers[0] intValue];
On the other hand when you have an array of strings ...
NSArray *arrayOfStrings = #[#"1", #"2", #"3"];
... you want to access individual elements directly, without converting the string object to something else:
NSString *element = arrayOfStrings[0];
NSString objects do not understand the stringValue method:
[arrayOfStrings[0] stringValue]; // crash: does not recognize selector
Back at the beginning, our NSNumber objects from the first array do understand stringValue. You can use it to convert the number to a string:
NSString *intString = [arrayOfNumbers[0] stringValue];
To make the confusion perfect, NSString also understand the intValue message:
int value = [arrayOfStrings[0] intValue];
Here intValue means to try to convert the string to a plain C int value.
The error you will be getting (but failing to post with your question) will be Unknown selector sent to instance and this is because NSString doesn't have a stringValue method.
The approach you suggest is correct:
NSString *v0 = [arrayObj objectAtIndex:0];
EDIT (prompted by #Answerbot's answer):
The reason you are confused is that [NSString intValue] is used to convert the string value to an integer, as long as the string represents an integer (i.e. #"123"). However you don't need this for string as the object is already a string. It's therefore not provided.
Is it possible to cast a NSInteger to a NSNumber object?
I need to convert the tag of a UIImageView object to a NSNumber object because I need to pass it as an argument to a function.
You cannot cast it because NSInteger is not an object, just an alias for a built-in type. You can always create a new NSNumber object from NSInteger, like this:
NSNumber *myNum = #(myNsIntValue);
or in the prior version of the compiler, use
NSNumber *myNum = [NSNumber numberWithInteger:myNsIntValue];
since Apple LLVM Compiler 4.0, there is an easier way to create NSNumber object:
NSNumber *x = #1234;
NSNumber *y = #(anIntegerVariable);
This is the more correct answer and it will not produce unexpected error.
NSNumber *myNum = [NSNumber numberWithInteger:myNsIntValue];
Because the doc said:
"numberWithInteger:
Creates and returns an NSNumber object containing a given value, treating it as an NSInteger."
"numberWithInt:
Creates and returns an NSNumber object containing a given value, treating it as a signed int."