CODEWITHSUNDEEP
c#winforms
user3182827
user3182827

Reputation: 13

Invalid argument error in c#

I am running into the following problem. I don't know what i'm doing wrong. It shows me an error "The best overloaded method match for 'System.Data.Common.DbDataReader.GetString(int)' has some invalid arguments."

Here is my code:

 SqlDataReader myReader;

      mycon.Open();
      myReader = cmdDatabase.ExecuteReader();
      while (myReader.Read())
         { 
          string cName = myReader.GetString("C_Name");

          textBox2.Text=cName;
         }

Upvotes: 1

Views: 1700

Answers (4)

Mitch
Mitch

Reputation: 22311

As has been mentioned several times now, the signature of GetString requires an integer representing the column index. You can translate the column name to its ordinal position using GetOrdinal.

Therefore, you can get the string value of the "C_NAME" column by using myReader.GetString(myReader.GetOrdinal("C_NAME")).

SqlDataReader also overrides the indexer, which lets you write the same as (string)myReader["C_Name"]

Complete example:

var sqc = new SqlCommand("SELECT C_NAME from table", con);
using (var reader = sqc.ExecuteReader())
{
    while (reader.Read())
    {
        int ordinal = reader.GetOrdinal("C_NAME");
        string byOrdinal = reader.GetString(ordinal);
        string byIndexer = (string)reader["C_NAME"];

        Console.Writeline("Column {0}, has the value of {1} (which is the same as {2})",
            ordinal, byOrdinal, byIndexer);
    }
}

You should also be careful to wrap your readers in using statements to ensure you don't leak database connections or run into a case where you consider enabling MARS.

Upvotes: 2

Grant Winney
Grant Winney

Reputation: 66511

The GetString method only accepts an int. You're passing it a string.

From MSDN, the parameter (an integer) represents "the zero-based column ordinal."

If C_Name is the first column (for example), you'd want to call:

string cName = myReader.GetString(0);

Upvotes: 3

Avi Turner
Avi Turner

Reputation: 10456

As the error indicates, you are trying to use an overload of the GetString which does not exist.

You are passing a string argument, while the method is expecting an integer that represents the index of the requested column.

You can read more about the method in the dcumetnation

Try changing your code to something like:

int indexOf cNameIdx = 5;// replace this with the real index from your select query
string cName = myReader.GetString(cNameIdx );

Upvotes: 1

Mitch Wheat
Mitch Wheat

Reputation: 300827

Look at the signature of GetString():

 System.Data.Common.DbDataReader.GetString(int)

It takes an integer ordinal (i.e. zero-based position) and you are trying to pass a string. There are no overloads which take a single string parameter.

Upvotes: 1

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