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i want to save the datagridview data to CSV but dont know the idea to chang the date format from 2022/03/07 00:00 to 2022/03/07.

What I have tried:

private void button7_Click(object sender, EventArgs e)
     {
    
     try
          {
              string csv = string.Empty;
              string HeaderText = string.Empty;
             foreach (DataGridViewColumn column in tableDataGridView.Columns)
                 {
                     csv += column.HeaderText + ',';
    
                 }
                 csv += "\r\n";
                 foreach (DataGridViewRow row in tableDataGridView.Rows)
                 {
                    foreach (DataGridViewCell cell in row.Cells)
                        {
                            if (cell.Value != null)
    
                             {
                   
           csv += cell.Value.ToString()/*.TrimEnd(',')*//*.Replace(",", ";") */+ /*','*/",";
                               
    
                         }
                            
                     }
                     csv += "\r\n";
                 }
    
    
                 string folderPath = "C:\\CSV\\";
                 if (!Directory.Exists(folderPath))
                 {
                     Directory.CreateDirectory(folderPath);
                 }
    
                 {
    
    
                  File.WriteAllText(folderPath + DateTime.Now.ToString("yyyyMMdd_HH-mm-ss") + ".csv", csv, Encoding.UTF8);
    
    
                     textBox3.Text = "保存しました";
                     textBox3.BackColor = Color.Green;
                 }
             }
Posted
Updated 6-Mar-22 21:06pm

1 solution

You have other problems you need to sort out first:
1) Don't use the DataGridView itself directly unless you really have to - use the underlying DataSource instead. That way, you get access to the actual data fields more easily.
2) Your column headers line ends with a spurious comma: consider using string.Join[^] instead of a manual loop.
C#
if (myDataGridView.DataSource is DataTable dt)
    {
    string s = string.Join(",", dt.Columns.Cast<DataColumn>().Select(c => c.ColumnName));
    Console.WriteLine(s);
    }

3) Your row data isn't separated by a comma at all! Again, string.Join is your friend here.
4) Strings are immutable in .NET: each time you try to add two strings, you cause a new memory allocation and two copy operations - which can get extremely time- and memory-consuming with large data sets. Use a StringBuilder[^] instead.
5) Instead of a "blanket" ToString operation to build the CSV row data, check the datatype: if it's a DateTime, then use a specific ToString to convert it.

C#
if (myDataGridView.DataSource is DataTable dt)
    {
    List<string> csvReady = new List<string>(dt.Rows.Count + 1);
    csvReady.Add(string.Join(",", dt.Columns.Cast<DataColumn>().Select(c => c.ColumnName)));
    List<string> rowData = new List<string>(dt.Columns.Count);
    foreach (DataRow row in dt.Rows)
        {
        rowData.Clear();
        for (int i = 0; i < dt.Columns.Count; i++)
            {
            object cell = row[i];
            if (cell.GetType() == typeof(DateTime))
                {
                rowData.Add(((DateTime)cell).ToString("yyyy/MM/dd"));
                }
            else
                {
                rowData.Add(cell.ToString());
                }
            }
        csvReady.Add(string.Join(",", rowData));
        }
    string csv = string.Join("\n", csvReady);
    }
   
v2

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