Operation

Conforming implementations do not throw an exception when format and/or formatProvider are null references. If formatProvider is a null reference, the string is constructed using a system-supplied formatting object containing information for the current system culture. If format is null, the string is constructed using a system-supplied default format appropriate for the type of the current instance.

If the object returned by formatProvider supplies a culture-specific representation of symbols or patterns included in format, the returned string is required to use the information supplied by formatProvider .

Note to Inheritors

The following example demonstrates using the IFormattable.ToString(string, IFormatProvider) method to display values in a variety of formats. The current system culture is U.S. English, which provides the default values for the formatProvider parameter of IFormattable.ToString(string, IFormatProvider).

using System;
class FormattableExample {
    public static void Main() {
    double d = 123.12345678901234;
    string[] formats = {"C","E","e","F","G","N","P","R"};
    for (int i = 0; i< formats.Length;i++) 
        Console.WriteLine("{0:R} as {1}:  {2}",d,formats[i],d.ToString(formats[i],null));

    string[]intFormats = {"D","x","X"};
    int val = 255;
    for (int i = 0; i< intFormats.Length;i++) 
        Console.WriteLine("{0} as {1}:  {2}",val,intFormats[i],val.ToString(intFormats[i],null));

    }
}

The output is