CType Function (Visual Basic)
Returns the result of explicitly converting an expression to a specified data type, object, structure, class, or interface.
Any valid expression. If the value of expression is outside the range allowed by typename, Visual Basic throws an exception.
Any expression that is legal within an As clause in a Dim statement, that is, the name of any data type, object, structure, class, or interface.
You can also use the following functions to perform a type conversion:
CType is compiled inline, which means that the conversion code is part of the code that evaluates the expression. In some cases, the code runs faster because no procedures are called to perform the conversion.
If no conversion is defined from expression to typename (for example, from Integer to Date), Visual Basic displays a compile-time error message.
If a conversion fails at run time, the appropriate exception is thrown. If a narrowing conversion fails, an OverflowException is the most common result. If the conversion is undefined, an InvalidCastException in thrown. For example, this can happen if expression is of type Object and its run-time type has no conversion to typename.
If the data type of expression or typename is a class or structure you've defined, you can define CType on that class or structure as a conversion operator. This makes CType act as an overloaded operator. If you do this, you can control the behavior of conversions to and from your class or structure, including the exceptions that can be thrown.
The CType operator can also be overloaded on a class or structure defined outside your code. If your code converts to or from such a class or structure, be sure you understand the behavior of its CType operator. For more information, see Operator Procedures (Visual Basic).
The following example uses the CType function to convert an expression to the Single data type.