How to print message in SQL output parameter

Question

I have a stored procedure like below. How I can print the message in the output parameter @ErrorMsg in my aspx page.

ALTER PROC [dbo].[ItemMasterIns]
(
    @ItemCode VARCHAR(30),
    @ItemDesc VARCHAR(100),
    @ErrorMsg VARCHAR(200) OUTPUT     
)
AS
BEGIN
     IF EXISTS ( SELECT 'X' FROM [DataBase].[dbo].[Table] WHERE Code= @Code )
     BEGIN
            SET @ErrorMsg = 'GIVEN CODE EXIST!'
            RETURN 0
     END
     ELSE
     BEGIN
            INSERT INTO [DataBase].[dbo].[Table]([Code], [Descr])
            VALUES (@Code, @Desc)
     END                   
END         

Answer 1

If you want to get the [@errormessage] and print it on ASPX page, then you need to use ParameterDirection.Output

Basing on your comment, I write a full code and tested it on my local, it works as expected. Please try again.

    using System;
    using System.Data;
    using System.Data.SqlClient;

    namespace ConsoleApplication2
    {
        class Program
        {
            static void Main(string[] args)
            {
                Program.RunSPWithParameterOutput();
            }

            public static void RunSPWithParameterOutput()
            {
                string PredefinedConnectionString = "Data Source=localhost;Initial Catalog=Adventure;Integrated Security=SSPI";

                using (SqlConnection conn = new SqlConnection(PredefinedConnectionString))
                using (SqlCommand cmd = new SqlCommand("dbo.usp_ItemMasterIns", conn))
                {
                    cmd.CommandType = CommandType.StoredProcedure;

                    // set up the parameters
                    cmd.Parameters.Add("@ItemsCode", SqlDbType.VarChar, 30);
                    cmd.Parameters.Add("@ItemsDesc", SqlDbType.VarChar, 30);
                    cmd.Parameters.Add("@ErrorMessage", SqlDbType.VarChar, 200).Direction = ParameterDirection.Output;

                    // set parameter values
                    cmd.Parameters["@ItemsCode"].Value = "test";
                    cmd.Parameters["@ItemsDesc"].Value = "test";

                    // open connection and execute stored procedure
                    conn.Open();
                    cmd.ExecuteNonQuery();

                    // read output value from @ErrorMessage
                    string ErrorMessage = cmd.Parameters["@ErrorMessage"].Value.ToString();
                    Console.WriteLine(ErrorMessage);
                    conn.Close();
                }
            }
        }
    }

Test store procedure deployed on my local.

    create procedure usp_ItemMasterIns (@ItemsCode varchar(100),
                                        @ItemsDesc varchar(30),
                                        @ErrorMessage varchar(200) output
                                        )
    as 
    begin 
        set @ErrorMessage='test error message'
    end