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Is there a better way to validate an integer in C # than Double.TryParse?

Double.TryParse returns a value and I don't need a value. I need to find out if a string is numeric and just return bool.

Is there a way to do this?

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6 answers


I would definitely think what you need to define. "Is a number" is more uncertain than meets the eye. Consider the following lines and whether you want to count them as numeric:

  • "NaN"
  • "Nan"
  • "infinity"
  • "0.000000000000000000000000000000000000000000000000001"
  • "1e5"
  • "1e500"
  • "1000"
  • "+ 1"

Using Double.TryParse

(with en-GB culture - don't forget cultural issues!) Will give you True, False, True, True (although not imaginable), True, False. True true.

If you want to know if a later call will Double.TryParse

succeed, calling it here would be the most accurate solution. If you are using some other criteria, a regex may be more appropriate. An example of criteria you can use:



  • May be + or -, but only in the first character
  • There can be one period for any symbol. You might want to avoid the one at the end - followed by "1." acceptable?
  • Apart from the above, all characters must be numbers

This will be prohibited to everyone except the fourth and final example above.

EDIT: Now I noticed that the title of the question includes "integer". This greatly reduces the checking of specifications for:

  • Do you want to allow leading zeros (e.g. -00012)?
  • What is the range?
  • Do you only want decimal places (instead of hex, etc.)?
  • Do you need to accept thousands separators?
  • What is your policy for leading / trailing spaces?
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Well, you can use a regex, but why not just drop the value from Double.TryParse and move on? I don't think it will be worth the effort trying to duplicate this code.



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One way is to add a link to Microsoft.VisualBasic

and then useInformation.IsNumeric(). 

using Microsoft.VisualBasic;

...

if (Information.IsNumeric("1233434.0"))
{
    Console.WriteLine("Yes");
}
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How about a regular expression?

string s = "13.2";
bool bIsDecimal = Regex.IsMatch("^-?\d+(\.\d+)?$");

should check if it is a decimal value. What it won't tell you is whether it is a valid decimal number, as in, whether the number will match in the decimal range.

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I just released Visual Studio Express (2005 and 2008). Intellisense says the return value of Double.TryParse () is a bool. The following worked for me on limited testing ...

double res; // you must be under very resource-constrained 
            // conditions if you can't just declare a double
            // and forget about it

if (Double.TryParse(textBox1.Text, out res)) {
    label1.Text = "it a number";
} else {
    label1.Text = "not a number";
}
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try doing this isnumeric:

public static bool IsNumeric(object Expression)

{

  bool isNum;

  double retNum;

  isNum = Double.TryParse(Convert.ToString(Expression), System.Globalization.NumberStyles.Any,System.Globalization.NumberFormatInfo.InvariantInfo, out retNum );

  return isNum;

}

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