In C#, would something like this work? Key is setting the length of the input parameter when you create it. You didn't indicate what type @o is so I assumed it was int.

private int CallProc(int inputParmLength, string inputParmValue)

{

int outputValue = -1;

using (SqlConnection conn = new SqlConnection("[your connection string here]"))

{

SqlCommand cmd = new SqlCommand();

cmd.CommandType = CommandType.StoredProcedure;

cmd.CommandText = "xp_test";

SqlParameter parm1 = new SqlParameter("@i", SqlDbType.VarChar, inputParmLength);

SqlParameter parm2 = new SqlParameter("@o", SqlDbType.Int);

parm1.Value = inputParmValue;

parm2.Direction = ParameterDirection.Output;

cmd.Parameters.Add(parm1);

cmd.Parameters.Add(parm2);

conn.Open();

int affectedRows = cmd.ExecuteNonQuery();

outputValue = (int)cmd.Parameters["@o"].Value;

conn.Close();

}

return outputValue;

}