Casting when dealing with nullable fields in a SqlDataReader

When dealing with nullable fields in a SqlDataReader, use:

int? field_a = reader["field_a"] as int?;
string field_b = reader["field_a"] as string;

instead of:

int? field_a = Convert.ToInt32(reader["field_a"]);
string field_b = Convert.ToString(reader["field_a"]);

http://stackoverflow.com/questions/2141575/how-to-efficiently-convert-cast-a-sqldatareader-field-to-its-corresponding