String to double, precision lost - iphone

I have 53.025709438664 in string when I do [string_variable doubleValue], I get 53.025709.
I use NSLog(#"%f") to print it.
How I can get full precision value ?

Please have a look at the format specifiers provided in Apple doc.
You cannot get all the digits after decimal point.
Edit:
If you know exact number of digits after decimal, then we could use something as follows
NSString *s = #" 53.025709438664";
double d = [s doubleValue];
NSLog(#"%.12f",d);

Related

formatting NSDecimalNumber issue

I'm trying to create NSDecimalNumber with simply format like: 123.00 with two fractional digits after dot, always. I tried use the NSFormatter and many other ways like converting float from string and creating then NSDecimalNumber from this string, but it's not working.
The problem is that I need only NSDecimalNumber in this format, not NSString or any other.
Thanks for any advice,
Paul
You may get idea from this.
float num = 123.1254546;
NSString *str = [NSString stringWithFormat:#"%.2f",num];
NSLog(#"%.2f %#",num,str);
I think you simply need to do Type Casting operation for Two times as bellow
float value = 123.562;
int myDigit = value;
it gives value 123 in myDigit variable
NSLog(#"MyDigit in Decimal = %d",myDigit);
Output is MyDigit in Decimal = 123
now if you want output like 123.000 then simply write as bellow
float valueWithZiro = myDigit;
NSLog(#"MyDigit with 000 == %3f",valueWithZiro);
Output is MyDigit in Decimal = 123.000
NSDecimalNumber, like NSNumber, cannot contain formatting information. The object structure simply doesn't support it. It represents a number, not the way the number is displayed.
You can convert it to a formatted NSString (which you say you don't want). But you can't do what you're asking.
You convert it to a formatted NSString using an NSNumberFormatter. It's the object that allows you to specify the decimal and thousands separators, number of decimal places to display, the currency symbol, etc.
Maybe you were looking to store a NSNumberDecimal with just two digits after the fraction?
If so NSDecimalNumberBehaviors is your friend.
I had a similar need and used the following:
self.decimalHandlingBehaviorForApp = [NSDecimalNumberHandler
decimalNumberHandlerWithRoundingMode:NSRoundUp
scale:2 raiseOnExactness:NO
raiseOnOverflow:NO raiseOnUnderflow:NO
raiseOnDivideByZero:YES];
Edit: added example of using it
// update the taxable total first
self.cartTaxableTotal = [self.cartTaxableTotal decimalNumberByAdding:itemAdded.priceOfItem
withBehavior:self.decimalHandlingBehaviorForApp];

How to convert NSDecimalNumber to CLLocationDegrees without losing precision?

I need to convert NSDecimalNumber with lat/lon values which I need to convert to CLLocationDegrees. I used -[NSDecimalNumber doubleValue] method. But the value loses its precision. I want the values to be same. The following is what I am talking about(I hope everyone would be aware about this issue already).
NSString *coordStr = #"-33.890934125621094";
NSDecimalNumber *lat = [NSDecimalNumber decimalNumberWithString:coordStr];
NSLog(#"%#", lat); // -33.890934125621094
NSLog(#"%lf", [lat doubleValue]); // -33.890934
Is there any way that I should do instead of doing the above?
Try out to convert the String with the doubleValue method
NSString *coordStr = #"-33.890934125621094";
NSLog(#"%.17g",coordStr.doubleValue); //-33.890934125621094
Check out this post: How to print a double with full precision on iOS?
edit:
the docu says: typedef double CLLocationDegrees; so you can double test = coordStr.doubleValue; the problem is only, that NSLog doesn't print the complete value. but instead the double var saves the complete value.
CLLocationDegree is a double. So the maximum precision can only equal that of a double datatype.

objective-c stringvalue from double

I have the following code:
double d1 = 12.123456789012345;
NSString *test1 = [NSString stringWithFormat:#"%f", d1]; // string is: 12.123457
NSString *test1 = [NSString stringWithFormat:#"%g", d1]; // string is: 12.1235
How do I get a string value that is exactly the same as d1?
It may help you to take a look at Apple's guide to String Format Specifiers.
%f 64-bit floating-point number
%g 64-bit floating-point number (double), printed in the style of %e if the exponent is less than –4 or greater than or equal to the precision, in the style of %f otherwise
Also read up on floating point (in)accuracy, and, of course What Every Computer Scientist Should Know About Floating-Point Arithmetic.
If you really want the string to match the double exactly, then use NSString to encode it and call doubleValue when you want the value. Also take a look at NSNumberFormatter.
How about
NSString *test1 = [NSString stringWithFormat:#"%.15f", d1];
Or simply go for the double as
NSString *test1 = [NSString stringWithFormat:#"%lf", d1];

Removing characters after the decimal point for a double

How can I remove the all the characters after the decimal point.
Instead of 7.3456, I would just like 7.
This is what I do to get the number so far with decimal places.
[NSString stringWithFormat:#" %f : %f",(audioPlayer.currentTime),(audioPlayer.duration) ];
Many Thanks,
-Code
You can specify what you want using format string :
[NSString stringWithFormat:#" %.0f : %.0f", (audioPlayer.currentTime),
(audioPlayer.duration)];
If you want this for display, use an NSNumberFormatter:
double sevenpointthreefourfivesix = 7.3456;
NSNumberFormatter * formatter = [[NSNumberFormatter alloc] init];
[formatter setMaximumFractionDigits:0];
NSLog(#"%#", [formatter stringFromNumber:[NSNumber numberWithDouble:sevenpointthreefourfivesix]]);
2011-12-20 20:19:48.813 NoDecimal[55110:903] 7
If you want a value without the fractional part, use round(). If you want the closest integer value not greater than the original value, use floor().
floorf() is the function you're looking for.
you are after
[NSString stringWithFormat:#" %.00f : %.00f",(audioPlayer.currentTime),(audioPlayer.duration) ];
When formatting float you can tell the precision by the number before the f
Cast to int:
[NSString stringWithFormat:#" %i : %i",(int)(audioPlayer.currentTime),(int)(audioPlayer.duration) ];
Casting like this always rounds down (eg: just removes everything after the decimal place). This is what you asked for.
In the case of rounding to the NEAREST whole number you want to add 0.5 to the number
[NSString stringWithFormat:#" %i : %i",(int)(audioPlayer.currentTime+0.5f),(int)(audioPlayer.duration+0.5f) ];
This will round to the nearest whole number. eg: 1.2 becomes 1.7 and casting to int makes 1. 3.6 becomes 4.1 and casting makes 4. :)
Why not just cast the audioPlayer.currentTime to an integer before you use stringWithFormat?
[NSString stringWithFormat:#"%d", (int)(audioPlayer.currentTime)];
All you need to do is type-cast the double to an int, like so: int currentTime_int = (int)audioPlayer.currentTime;.
You can use this same approach for the other variable.
Many of the shorter answers here will work correctly. But if you want your code to be really clear and readable, you might want to explicitly specify your desired conversion from float to int, such as using:
int tmpInt = floorf(myFloat); // or roundf(), etc.
and then separately specifying how you want the integer formated, e.g.
... stringWithFormat:#"%d", tmpInt ... // or #"%+03d", etc.
instead of assuming that an inline cast shows what you want.
You may also use
double newDvalue =floor(dValue);
it will remove all the decimals point
using %.0f for string format will be good also

NSDecimalNumber to unsignedLongLong - wrong value

Here is code:
NSNumber* number = [NSDecimalNumber decimalNumberWithString :#"11111111111111111"];
NSLog(#"%# = %lld", number, [number unsignedLongLongValue]);
And I get output:
11111111111111111 = 11111111111111112
Is it known bug or I do something wrong?
UPDATE:
bug reported: https://bugreport.apple.com/cgi-bin/WebObjects/RadarWeb.woa/3/wo/Stnn5Aaocknzx52c64zbN0/5.83.28.0.9
I believe the issue is that you are using NSNumber's -longLongValue method on an NSDecimalNumber. NSDecimalNumber stores a high-precision representation of the number internally as a decimal, but NSNumber just keeps it as an IEEE 754 double precision floating-point value. If I recall correctly, if you use the standard NSNumber superclass methods on an NSDecimalNumber, the internal number is first converted to a double, which can introduce binary floating-point artifacts like this.
As neoneye suggests, a way around this might be to use an NSString as an intermediary. For example:
NSDecimalNumber* number = [NSDecimalNumber decimalNumberWithString :#"11111111111111111"];
double number2 = [#"11111111111111111" doubleValue];
NSLog(#"%# = %lld = %f", number, [[number descriptionWithLocale:nil] longLongValue], number2);
Will produce the result 11111111111111111 = 11111111111111111 = 11111111111111112.000000, showing both the correct result from the decimal number extraction and the error that happens when this number is temporarily stored in a double.