Finally we cast that same reference with the as-operator. C program that uses casts using System; using System. WriteLine builder. Implicit casts are not visible in the source text.
The explicit int on the left side of a variable or expression casts to an int. Example: Here the integer cast succeeds.
But we then try to cast to an invalid type. Warning: If you incorrectly use a cast expression, you will cause an InvalidCastException to be thrown. Implicit casts: Intended never to provoke an exception. These are used when a value is expanded to more bytes. Explicit casts: Allowed to provoke an exception.
Explicit casts are used when a value is reduced to fewer bytes. InvalidCastException: Unable to cast object of type 'System. Int32' to type 'System. Main Convert. A List is not an array. This is no problem unless we need an array. Conversions are possible for both simple values and complex data types. Examples: These examples show how to convert types. The provided conversions are more complex than casts. Here: In this program, we use an extension from the System.
Linq namespace to convert an array into a List. ToCharArray: This method is provided on the string class. It returns the underlying buffer of a string as a char array. C also provides the is and as operators to test if a value is of a certain type. The preceding sample demonstrates a few features of pattern matching syntax. The if a is Mammal m statement combines the test with an initialization assignment.
The assignment occurs only when the test succeeds. The variable m is only in scope in the embedded if statement where it has been assigned. You can't access m later in the same method. The preceding example also shows how to use the as operator to convert an object to a specified type. You can also use the same syntax for testing if a nullable value type has a value, as shown in the following example:. For example, a Boolean, or bool , variable can only be either true or false.
However, in some applications a variable value can be undefined or missing. For example, a database field may contain true or false , or it may contain no value at all, that is, NULL. You can use the bool? As a value type is implicitly convertible to the corresponding nullable value type, you can assign a value to a variable of a nullable value type as you would do that for its underlying value type. You can also assign the null value. For example:. HasValue property returns false.
Beginning with C 7. You always can use the following read-only properties to examine and get a value of a nullable value type variable:. HasValue indicates whether an instance of a nullable value type has a value of its underlying type. Value gets the value of an underlying type if HasValue is true. The following example uses the HasValue property to test whether the variable contains a value before displaying it:.
You can also compare a variable of a nullable value type with null instead of using the HasValue property, as the following example shows:. If you want to assign a value of a nullable value type to a non-nullable value type variable, you might need to specify the value to be assigned in place of null.
Use the null-coalescing operator?? The Test method has an Animal parameter, thus explicitly casting the argument a to a Reptile makes a dangerous assumption. It is safer to not make assumptions, but rather check the type. C provides the is operator to enable you to test for compatibility before actually performing a cast. For more information, see How to safely cast using pattern matching and the as and is operators. For more information, see the Conversions section of the C language specification.
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