"Specified cast is not valid" error in C# windows forms program

Question

I'm having a "Specified cast is not valid" error. Windows form application in C#. I'm trying to retrieve a value from a table. The value is either a smallint, or a numeric(i tried both fields, both give me the same error), and I try to store it in an int variable.

here's the source:

using (SqlDataReader rdr = cmd.ExecuteReader()) //"select * from table where fieldname = " + value
{

 while (rdr.Read())
 {
  int number = (int)rdr["quantity"]; // error is here

Answer 1

Try one of the two options.

int number = rdr.getInt32(rdr.GetOrdinal("quantity"));

or

int number = int.parse(rdr["quantity"].ToString());

Answer 2

  if(rdr["quantity"].GetType() != typeof(int))
    throw new InvalidOperationException(
      "quantity is a " + rdr["quantity"].GetType());
  int number = (int)rdr["quantity"]; // error is here

Answer 3

Have you tried int number=convert.toint16(rdr["quantity"]);

Answer 4

rdr["quantity"] is going to be a boxed something. If it is not an int then you can not unbox it directly to an int (which is what you are trying to do) as you have to first unbox it to the appropriate type (say, short). But this is too cumbersome so for clarity you're better off saying

Convert.ToInt32(rdr["quantity"]);

Answer 5

I bet quantity is NULL, which is not an integer.

Answer 6

Try using SqlDataReader's GetInt32()

rdr.GetInt32(rdr.GetOrdinal("quantity"));

Answer 7

Silly suggestion, maybe - but have you considered trying this - grab the result from your SqlDataReader as an instance of object and then checking what type it is? No one can tell you better what it really is than the CLR type system! :-)

using (SqlDataReader rdr = cmd.ExecuteReader()) 
{
    while (rdr.Read())
    {
        object obj = rdr["quantity"];

        if(obj != null)
        {
            string objType = obj.GetType().FullName;
        }
    }
 }

If you do get a value back, you can check what type it is and hopefully convert it accordingly, depending on your results.

Answer 8

Since you said that you know what the value should be because you created the database... Can you check that rdr["quantity"] has a value then run a try parse on it?

if(rdr["quantity"] != null) {
    int? number = null;
    if(int.TryParse(rdr["quantity"].ToString(), out number)) {
        Console.WriteLine("Hurray, I have an int. Up vote Coov!");
    }
}