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 +,-,.

Answer 1

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 2

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);

Answer 3

You could use code like this:

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

If your object is an Int32, Single, Double etc. it will perform the conversion. Also, a string implements IConvertible but if the string isn't convertible to a double then a FormatException will be thrown.

Answer 4

There are some great answers above. Here is an all-in-one solution. Three overloads for different circumstances.

// Extension method, call for any object, eg "if (x.IsNumeric())..."
public static bool IsNumeric(this object x) { return (x==null ? false : IsNumeric(x.GetType())); }

// Method where you know the type of the object
public static bool IsNumeric(Type type) { return IsNumeric(type, Type.GetTypeCode(type)); }

// Method where you know the type and the type code of the object
public static bool IsNumeric(Type type, TypeCode typeCode) { return (typeCode == TypeCode.Decimal || (type.IsPrimitive && typeCode != TypeCode.Object && typeCode != TypeCode.Boolean && typeCode != TypeCode.Char)); }

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.