Store NSNumber in a long double type

Question

I have a number stored in an NSNumber which I would like to put into a long double , like so:

NSNumberFormatter * f = [[NSNumberFormatter alloc] init]; 

[f setNumberStyle:NSNumberFormatterDecimalStyle]; 

[f setMinimumSignificantDigits:5];

NSNumber * myNumber = [f numberFromString:@"1.1234567899"]; 

long double lnumber = mynumber;
NSLog(@"%Lf ",lnumber);

Answer 1

An NSNumber is an Objective-C object, and long double is a primitive type. You can't assign an object to a primitive-typed variable. If you want the numerical value that is stored in the NSNumber , you need to use one of its methods to retrieve it:

long double lnumber = [myNumber doubleValue];

There is no provision for storing a long double in an NSNumber ; the largest floating-point type is simply double . It seems that long double may be the same size as double on iOS anyways: see this Apple Support Forum thread .

As ThomasW mentioned , NSDecimalNumber , a fixed-point number class, offers both more precision (up to 38 digits) and accuracy than NSNumber . There is still no way to get a long double out of it, though; you would have to do all your math only with NSDecimalNumber s to retain the precision.

Your question title originally mentioned NSInteger as well, although the body didn't, so let me add this note. An NSInteger is a primitive type, like long double , so you can in fact assign from one to the other.

NSInteger myInteger = 10000;
long double lnumer = myInteger;

However, because it is an integer, it can't have a fractional part.

Answer 2

As far as I know the best you are going to get is a double value.

long double lnumber = [mynumber doubleValue];

You can also do this if the value is in a string to begin with

NSString* sval = @"1.1234567";
double dval = [sval doubleValue];

Answer 3

Unfortunately you can't. As NSNumber Class Reference says, NSNumber supports double and float but not long double .

Answer 4

If you need high precision you could use NSDecimalNumber , but it doesn't support long double either.

http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSDecimalNumber_Class/Reference/Reference.html

Answer 5

尝试输出数字：

long double lnumber = (long double) mynumber;