Insert CSV from file upload control directly to memory stream without physical path

I know this is an old question, but the below code will work for reading your posted text file into a memory stream using a StreamReader and is compatible with .NET 4.0:

protected void ReadCsv()
{
    StreamReader reader = new StreamReader(ctrlFileUpload.PostedFile.InputStream);
    string content = reader.ReadToEnd();
}

Note, this method is only efficient if you have enough memory on the server to handle larger files for multiple users concurrently. You don't want to use this approach if you have hundreds of users posting files simultaneously to a memory stream and causing your server to crash due to insufficient available memory. You'll also want to check if this is an acceptable method if you're on a shared hosting environment.

Does this help?

This should give you the stream. So you'd make your ReadCsv method accept a reference to the stream, and pass that to it rather than the filename, and work against the stream.

MSDN FileUpload.FileContent Property

//Try below one to capture data in MemoryStream from FileUpload Control

  protected void btnFileUpload_Click(object sender, EventArgs e)
    {
        if (FileUploadControl.HasFile)
        {
            try
            {                 
                #region Capture file data in Memory Stream

                byte[] fileData = null;
                Stream fileStream = null;
                int length = 0;

                length = FileUploadControl.PostedFile.ContentLength;
                fileData = new byte[length + 1];
                fileStream = FileUploadControl.PostedFile.InputStream;
                fileStream.Read(fileData, 0, length);

                //Use MemoryStream to capture file data
                MemoryStream stream = new MemoryStream(fileData);

                Session["FileUploaded"] = stream;

                #endregion

                StreamReader strFile;                 

                using (strFile = new StreamReader(stream))
                {
                    string line;
                    DataTable dtStudentData = CreateDataTable();
                    DataRow drStudentRow;
                    List<String> errorMessages = new List<String>();
                    // Read and display lines from the file until the end of the file is reached. 
                    while ((line = strFile.ReadLine()) != null)
                    {
                        if (line.Trim().Length > 0)
                        {
                            System.Threading.Thread.Sleep(1000);
                            string[] columns = line.Split('\t'); //splitting the line which was read by the stream reader object                                  

                            Int32 charpos = (Int32)strFile.GetType().InvokeMember("charPos", BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.GetField, null, strFile, null);

                            Int32 charlen = (Int32)strFile.GetType().InvokeMember("charLen",
                            BindingFlags.DeclaredOnly |
                            BindingFlags.Public | BindingFlags.NonPublic |
                            BindingFlags.Instance | BindingFlags.GetField
                             , null, strFile, null);

                            int lineno = (Int32)strFile.BaseStream.Position - charlen + charpos;                                

                            //Add data row in Data Table
                            drStudentRow = dtStudentData.NewRow();  
                            // TO DO code - Fill data table
                            dtStudentData.Rows.Add(drStudentRow);
                        }                            
                    }
                    strFile.Dispose();
                    dtStudentData.Rows.RemoveAt(0); //Remove the first column since its the column name not necessary to insert in the database table
                    PopulateStudentInvalidDataGridView(dtStudentData);    // Bind Grid                    
                    Session["StudentData_FileParsedStudentRegistrtaionTable"] = dtStudentData;
                    strFile.Close(); //release the stream reader                        
                }
            }
            catch (Exception ex)
            {
                String error = ex.Message;
            }
        }
    }