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Determine if a String IsNumeric in C# | Ben Clark-Robinson

I’ve seen several implmentations of an IsNumeric() method in C# and all of them are woeful. Some examples involve casting and catch then catching exception, other (worse) examples recommend using Regular Expressions to check for only digits (no joke)!

Here’s a nice and simple Extension Method to determine if a string IsNumeric().

/// 
/// Determines whether the specified string is numeric.
/// 
public static bool IsNumeric(this string input)
{ double value; return double.TryParse(input, out value);
}

I’ve even got some very simple Unit Tests to go with it (I understand I should not unit test .NET, but I wanted to ensure my implementation was fine).

[TestMethod]
public void IsNumeric_Numeric_String_Should_Evaluate_True()
{ var expected = true; var text = "123456789.5";
  var actual = text.IsNumeric();
  Assert.AreEqual(expected, actual);
}
 
[TestMethod]
public void IsNumeric_Not_Numeric_String_Should_Evaluate_False()
{ var expected = false; var text = "123456789rabbits";
  var actual = text.IsNumeric();
  Assert.AreEqual(expected, actual);
}

Updated (5-June-2011): This method only tested whole numbers, decimals are now supported.

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