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.NET rounding error in ToString ("f2")

Hi, I have this code in C #:

float n = 2.99499989f;
MessageBox.Show("n = " + n.ToString("f2", CultureInfo.InvariantCulture));

And this code in C ++:

float n = 2.99499989f;
printf("n = %.2f", n);

The first prints 3.00 .
The second prints 2.99 .

I do not know why this is happening.

Update:

I also tried Objective-C NSLog , and the result is 2.99 .

I needed to fix it quickly, so I used the following method:

float n = 2.99499989f;
float round = (float)Math.Round(n, 2);
MessageBox.Show("round = " + round.ToString(CultureInfo.InvariantCulture));

This code shows 2.99 , but calculates the circle in double precision. I can not find Math.RoundF.

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6 answers

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, "printf" float double . float double, ToString ( "f2" ), float.

printf:

C float double ( , , , int printf...

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fooobar.com/questions/146402/...

, , 2.995F = 2.99499989F, , 2.995 .

, , , , 2.995 < > 2.99499989 , 2.995 ( ), , .

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+1

BitConverter.GetBytes , , - 0x403FAE14, 

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, printf ToString. , .

+6

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-, .

, ? 2.9949... 2.995?

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, "float" ""?

, :

        // float
        Console.WriteLine (2.99499989f.ToString ("f2"));
        // The above line outputs 3.00

        // decimal
        Console.WriteLine (2.99499989M.ToString ("f2"));
        // The above line outputs 2.99

, float 2.99499989 2,99.
, , :

// float
Console.WriteLine (2.98499f.ToString ("f2"));
// The above line outputs 2.99
0

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- 2.99499989f, 2.995. 2.994999 ( 2 ^ {- 23}, ), , 2.995

0

2.99499989f IEEE754. , printf ToString -.

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