C# Extension Method for String Data Type

Question

My web application deals with strings that need to be converted to numbers a lot - users often put commas, units (like cm, m, g, kg) and currency symbols in these fields so what I want to do is create a string extension method that cleans the field up and converts it to a decimal.

For example:

decimal myNumber = "15 cm".ToDecimal();

Answer 1

Are you expecting users of different 'cultures' to use your application? If so it's better to factor in the user's regional settings:

static decimal ToDecimal(this string str)
{
    return Decimal.Parse(str, CultureInfo.CurrentCulture);
}

Or you could replace every character in str that isn't a digit or the CultureInfo.CurrentCulture.NumberFormat.CurrencyDecimalSeparator value and then parse it as a decimal.

EDIT:
It is generally accepted that extension methods should have their own namespace. This will avoid naming conflicts and force the end user to selectively import the extensions they need.

Answer 2

An extension method is of the following form:

public static class StringExtensions
{
    public static decimal ToDecimal(this string input)
    {
        //your conversion code here
    }
}

• The containing class must be static. The method is also static Note the "this" keyword. I recommend the convention of grouping extension methods by the type to which they refer, but there is no requirement to do so.

Here is a guide for writing extension methods.