NSNumber value changing when JSON object is converted to data and then that data is again converted back to JSON object

Question

I am creating NSData object with a dictionary as follows,

dictionary:

{
    channelId = 201;
    lang = EN;
    reqRefNo = vZRIzNd;
    storeInfo =     {
        clientInfo =         {
            deviceId = XXXXXXXXA67F488B836D19D80EC4FD8D;
        };
        loginLogId = XXXXXXXX5CAD4A0DA06BE2F055929856;
        qrCodeInfo =         {
            itemDesc = "";
            itemName = hahsj;
            price = 106;
        };
        userInfo =         {
            storeId = 3252;
        };
    };
}

price = 106

NSData *data = [NSJSONSerialization dataWithJSONObject:paramDict options:kNilOptions error:nil];

Now I'm again converting it back to JSON object as follows,

NSDictionary* json = [NSJSONSerialization JSONObjectWithData:data
                                                         options:kNilOptions
                                                       error:&error];

But I'm getting wrong price this time.

converted dictionary

{
    channelId = 201;
    lang = EN;
    reqRefNo = vZRIzNd;
    storeInfo =     {
        clientInfo =         {
            deviceId = XXXXXXXXA67F488B836D19D80EC4FD8D;
        };
        loginLogId = XXXXXXXX5CAD4A0DA06BE2F055929856;
        qrCodeInfo =         {
            itemDesc = "";
            itemName = hahsj;
            price = "105.9999923706055";
        };
        userInfo =         {
            storeId = 3252;
        };
    };
}

price = "105.9999923706055"

Code for generating NSNumber,

//_amountTF.text = "S$1.06";
NSString *amount = [_amountTF.text stringByReplacingOccurrencesOfString:@"S$" withString:@""];
float amt = [amount floatValue];
amt *=100;
NSNumber *num = [NSNumber numberWithFloat:amt];

Can anyone please explain me the reason behind this? Thanks.

Is both datatype are same ? price = 106; and price = "105.9999923706055"; ? — Prashant Tukadiya, May 08 '18 at 07:36
@trungduc its normal NSMutableDictionary created by using setObject forkey method. — Sanket_B, May 08 '18 at 08:27
@PrashantTukadiya before converting to NSData its NSNumber, I don't know what happening after conversion. — Sanket_B, May 08 '18 at 08:30
@SanketBhavsar I have check a NSMutableDictionary like yours on my side but get no error. Maybe you did something else and you didn't know it. — trungduc, May 08 '18 at 08:38
It is a floating point precision problem. Use `double` or `CGFloat` instead of `float`. — LGP, May 08 '18 at 08:45
@LGP It's not working for CGFloat but it is working fine using double. Can you please explain what's happening here? — Sanket_B, May 08 '18 at 08:47

score 2 · Accepted Answer · answered May 08 '18 at 09:12

It is a floating point precision problem. Use double instead of float.

Your number is stored in a binary format that can't represent all decimal values exactly, so some values are "rounded" to its nearest binary value. When printing the number, it will convert your float to double first, then print it. The conversion to double will take your rounded binary representation and store with higher precision, making it high precision with low precision content in it. Printing this will show the approximation you got when using float precision.

NSString *amount = [_amountTF.text stringByReplacingOccurrencesOfString:@"S$" withString:@""];
double amt = [amount doubleValue];
amt *=100;
NSNumber *num = [NSNumber numberWithDouble:amt];

Read more: 'float' vs. 'double' precision

score 0 · Answer 2 · answered Feb 20 '20 at 10:01

0

while. creating dictionary add price Value:

price = [NSString stringWithFormat:@"106"]; or, int priceValue = 106; price = [NSString stringWithFormat:@"%d",priceValue];

Now converted dictionary. will be whatever you need.

answered Feb 20 '20 at 10:01

Pappu Kumar. Sharma

11
3

NSNumber value changing when JSON object is converted to data and then that data is again converted back to JSON object

2 Answers2