NSString to CLLocationDegrees to NSString is changing value

Question

I am fetching a latitude and longitude from a JSON API. These values are coming in as Strings.

I store the value in a CLLocationDegrees like this:

CLLocationDegrees lat = [[coordinates objectForKey:@"lat"] doubleValue];
CLLocationDegrees lon = [[coordinates objectForKey:@"lat"] doubleValue];

But when I later retrieve the values from lat and lon and put them into an NSString, the value has changed from what was provided by the JSON. The change is usually only the last few digits of the coordinate, but it is enough to cause a problem.

NSString *latitude = [[NSNumber numberWithDouble:lat] stringValue];
NSString *longitude = [[NSNumber numberWithDouble:lon] stringValue];

Basically, at this point, [coordinates objectForKey:@"lat"] is not equal to latitude.

Any tips about how to fix this would be appreciated

Answer 1

NSNumber stringValue is going to give you a default representation which generally only has 5 decimal places.

One option would to use stringWithFormat and use a format that matches the data you have from the original JSON.

NSString *latitude = [NSString stringWithFormat:@"%.7f", lat];

Adjust the format specifier to meet your exact needs.

Also keep in mind that going from the original string to a double could result in some loss of precision due to the nature of how floating point numbers are represented. There's nothing you can do about that except keep a reference to the original string if it is that important.