Convert "1.79769313486232E+308" to double without OverflowException?

Question

I have this string "1.79769313486232E+308" and am trying to convert it to a .NET numeric value (double?) but am getting the below exception. I am using Convert.ToDouble(). What is the proper way to do this conversion?

OverflowException: Value was either too large or too small for a Double

Answer 1

You may try double.Parse() or double.TryParse() rather than Convert.ToDouble(), but I'm not certain you'll get better results. Incidentally, the string that you provide is equal to double.MaxValue, which is (of course) the maximum value that can be contained in a double, so that's likely where your error is coming from. Floating-point numeric types are finicky, so I would assume that some sort of rounding is taking place and pushing it outside the bounds of the type.

You could also try the decimal data type. You may have better luck there.

Answer 2

That number is too big for a double, as the exception says. You are going to have to find a large number library to handle that for you, as there is nothing that I know of in the .Net library that handles very large numbers.

Answer 3

The problem is likely due to the fact that Double.MaxValue was converted to a string, and when the string is output, not all the digits are output, instead it is rounded. Parsing this value overflows the double.

Using Double.TryParse and subsequently checking equality on the string "1.79769313486232E+308" in case of failure and substituting Double.MaxValue should be a quick workaround, if you need to keep the string the way it is.

Answer 4

Unfortunately this value is greater than double.MaxValue, hence the exception.

As codekaizen suggests, you could hard-code a test for the string. A better (IMO) alternative if you're the one producing the string in the first place is to use the "r" format specifier. Then the string you produce will be "1.7976931348623157E+308" instead, which then parses correctly:

string s = double.MaxValue.ToString("r");
double d = double.Parse(s); // No exception

Obviously that's no help if you don't have control over the data - but then you should understand you're likely to be losing data already in that case.

Answer 5

Here is what I came up with. Thanks Jon Skeet and codekaizen.

private double convertToDouble(string str)
{
    double dbl;

    if (double.TryParse(str, out dbl))
        return dbl;

    if (str == "1.79769313486232E+308")
        return double.MaxValue;

    return double.MinValue;
}