Explicit casting problem

smfarooq · November 10th, 2010, 02:09 PM

Hi,
I have a problem to cast the object type variable to int type in following code:

object a = '1';
int i;
i = (int)a;
Console.WriteLine(i);
======================
O/P:

Unhandled Exception: System.InvalidCastException: Specified cast is not valid.

it give the error as above, what am I missing?

Please help me.
Thanks.

samjudson · November 10th, 2010, 02:56 PM

You can only 'cast' if the object is the type you are casting to or implements an implicit convertion operator (e.g. An int to a double.)

For what you want you'll want to use Convert.ToInt32().

smfarooq · November 12th, 2010, 04:49 PM

Thanks for reply,
I have read in the book that object is the root of all classes and any variable which has type of object can be cast to any type.
But (The code which I have posted) I have tried to check that it can be cast or not, and it did not cast to char. since I am confused in that if object it root then it should be cast to any type.

And I have used another code which works fine:

Code:

static void Main(string[] args)
{
	object a = '1';
	------ -
	int i;
	i = (char)a;
	    -------
//The type of 'a' was object then it is casted to char and then assign to int type to make 'a' as int type.
	int ii = 0;
	char aa = 'a';
	ii = (int)aa;
	Console.WriteLine(i);
	Console.WriteLine(ii);
}

Thanks..

Imar · November 14th, 2010, 07:54 AM

Quote:

I have read in the book that object is the root of all classes and any variable which has type of object can be cast to any type.

I hink you misunderstood that somehow. The first part is true, but the second isn't. So, all objects inherit Object, and can be cast to an object. However, you cannot just cast any type to any other type. Consider these hierarchies:

Code:

 
Vehicle
  Car
  Truck
 
Animal
  Goat
  Cow

Now, a Cow is an animal, so something like this should work:

Code:

 
Cow clarabelle = new Cow(); 
Animal animal = (Animal) cow;

This casts the Cow type to a more generic Animal type.

But would you expect this to work:

Code:

 
Cow clarabelle = new Cow(); 
Truck truck = (Truck) cow;

In other words, as Sam said: "You can only 'cast' if the object is the type you are casting to or implements an implicit convertion operator (e.g. An int to a double.)" You can cast a
Cow to an Animal or to an Object (because ultimately a Cow IS an Animal and it IS an Object), but not to "any type" or arbitrary other types such as Trucks, Vehicles or ints.

Your code works because there are conversions between ints and chars available that, if I am not mistaken, call Convert.ToInt32 under the hood.

Cheers,

Imar

smfarooq · November 15th, 2010, 03:39 PM

Thank you, Now I have understood, and your given solution in this problem is very helpful for me.

smfarooq · December 23rd, 2010, 07:29 AM

Hi,
what is the difference between controls and components in c #?

Plz help me,

Thankx

joefawcett · December 23rd, 2010, 07:50 AM

New questions under a new thread please. That helps people searching for answers among other things.