Casting: (NewType) vs. Object as NewType [duplicate]

Question

What is actually the difference between these two casts?

SomeClass sc = (SomeClass)SomeObject; SomeClass sc2 = SomeObject as SomeClass; 

Normally, shouldn't they both be explicit casts to the specified type?

Answer 1

The former will throw an exception if the source type can't be cast to the target type. The latter will result in sc2 being a null reference, but no exception.

[Edit]

My original answer is certainly the most pronounced difference, but as Eric Lippert points out, it's not the only one. Other differences include:

• You can't use the 'as' operator to cast to a type that doesn't accept 'null' as a value
• You can't use 'as' to convert things, like numbers to a different representation (float to int, for example).

And finally, using 'as' vs. the cast operator, you're also saying "I'm not sure if this will succeed."

Answer 2

Also note that you can only use the as keyword with a reference type or a nullable type

ie:

double d = 5.34; int i = d as int; 

will not compile

double d = 5.34; int i = (int)d; 

will compile.