C# 5.0 Programmer's Reference

Casting and Converting Values ❘ 735
The integer functions ToInt16, ToInt32, ToInt64, ToUInt16, ToUInt32, and ToUInt64 also provide
overloaded versions that take as parameters a string value and a base, which can be 2, 8, 10, or 16 to
indicate whether the string is in binary, octal, decimal, or hexadecimal, respectively. For example, the
following statement converts the binary value 00100100 into the integer value 36.
int value = Convert.ToInt32("00100100", 2)
The BitConverter class provides methods for converting variables to and from arrays of bytes.
Widening and Narrowing Conversions
In a widening conversion, the destination data type can hold any value held by the source data type. For
example, a long can hold any value that fits in an int, so the following code is a widening conversion.
int intValue = 100;
long longValue = intValue;
Because this conversion must succeed, no casting or other operation is required.
In a narrowing conversion, the destination data type may not hold any value held by the source
data type. For example, an int cannot necessarily hold any value that fits in a long, so the following
code is a narrowing conversion.
long longValue = 100;
int intValue = (long)longValue;
Because this is a narrowing conversion, the casting operator is required, and the operation may
throw an exception if the value cannot fit in the destination data type.
Converting Objects
Converting an object into a less derived ancestor class is a widening conversion, so it doesn’t require
casting. Conversely converting an object into a more derived descendant class is a narrowing conversion,
so it requires casting.
For example, suppose the Employee class is derived from the Person class. Then the following code
shows a widening conversion followed by a narrowing conversion.
Employee employee = new Employee();
Person person = new Person();
Employee employee2 = (Employee)person;
The as Operator
The as operator provides a shorthand for converting objects from one type to another. The following
code converts the value in variable person into a Student and saves it in variable student.
student = person as Student;
If the value cannot be converted into a Student (for example, if person is a Janitor), then the as
operator returns null.
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