Checking if an object is a number in C#

Question

I'd like to check if an object is a number so that .ToString() would result in a string containing digits and +,-,.

Is it possible by simple type checking in .net (like: if (p is Number))?

Or Should I convert to string, then try parsing to double?

Update:' To clarify my object is int, uint, float, double, and so on it isn't a string. I'm trying to make a function that would serialize any object to xml like this:

<string>content</string>

or

<numeric>123.3</numeric>

or raise an exception.

Answer 1

You will simply need to do a type check for each of the basic numeric types.

Here's an extension method that should do the job:

public static bool IsNumber(this object value)
{
    if (value is sbyte) return true;
    if (value is byte) return true;
    if (value is short) return true;
    if (value is ushort) return true;
    if (value is int) return true;
    if (value is uint) return true;
    if (value is long) return true;
    if (value is ulong) return true;
    if (value is float) return true;
    if (value is double) return true;
    if (value is decimal) return true;
    return false;
}

This should cover all numeric types.

Update

It seems you do actually want to parse the number from a string during deserialisation. In this case, it would probably just be best to use double.TryParse.

string value = "123.3";
double num;
if (!double.TryParse(value, out num))
    throw new InvalidOperationException("Value is not a number.");

Of course, this wouldn't handle very large integers/long decimals, but if that is the case you just need to add additional calls to long.TryParse / decimal.TryParse / whatever else.

Answer 2

Yes, this works:

object x = 1;
Assert.That(x is int);

For a floating point number you would have to test using the float type:

object x = 1f;
Assert.That(x is float);

Answer 3

Assuming your input is a string...

There are 2 ways:

use Double.TryParse()

double temp;
bool isNumber = Double.TryParse(input, out temp);

use Regex

 bool isNumber = Regex.IsMatch(input,@"-?\d+(\.\d+)?");

Answer 4

You could use code like this:

if (n is IConvertible)
  return ((IConvertible) n).ToDouble(CultureInfo.CurrentCulture);
else
  // Cannot be converted.

If your object is a string this will not parse the string. However, if your object is an Int32, Single, Double etc. it will perform the conversion.

Answer 5

There are three different concepts there:

• to check if it is a number (i.e. a (typically boxed) numeric value itself), check the type with is - for example if(obj is int) {...}
• to check if a string could be parsed as a number; use TryParse()
• but if the object isn't a number or a string, but you suspect ToString() might give something that looks like a number, then call ToString() and treat it as a string

In both the first two cases, you'll probably have to handle separately each numeric type you want to support (double/decimal/int) - each have different ranges and accuracy, for example.

You could also look at regex for a quick rough check.

Answer 6

Taken from Scott Hanselman's Blog:

public static bool IsNumeric(object expression)
{
    if (expression == null)
    return false;

    double number;
    return Double.TryParse(Convert.ToString(expression, CultureInfo.InvariantCulture), System.Globalization.NumberStyles.Any, NumberFormatInfo.InvariantInfo, out number);
}

Answer 7

Take advantage of the IsPrimitive property and generics to make a handy extension method:

public static bool IsNumber<T>(this T obj)
{
    Type objType = obj.GetType();

    if(objType.IsPrimitive)
    {
        if (objType == typeof(object) || 
            objType == typeof(string) || 
            objType == typeof(bool))
            return false;

        return true;
    }

    return false;
}

Answer 8

If your requirement is really

.ToString() would result in a string containing digits and +,-,.

and you want to use double.TryParse then you need to use the overload that takes a NumberStyles parameter, and make sure you are using the invariant culture.

For example for a number which may have a leading sign, no leading or trailing whitespace, no thousands separator and a period decimal separator, use:

NumberStyles style = 
   NumberStyles.AllowLeadingSign | 
   NumberStyles.AllowDecimalPoint | 
double.TryParse(input, style, CultureInfo.InvariantCulture, out result);