Excel CSV编码问题

Question

I have a question about danish characters and open saved file as CSV in Excel. See the code below:

        [HttpGet]
        [Route("/progress/data.csv")]
        [Produces("text/csv")]
        public IActionResult GetCSV()
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendLine("æø;2;3;");
            Encoding encode = Encoding.UTF8;
            return File(encode.GetBytes(sb.ToString()), "text/csv", "data.csv");
        }

I am using .NET Core 2.1 and the result of this export is that the two first characters æø are displayed as æà .

I am aware that this is a known problem but I have so far not found a solution for it. During the last 4 hours I have tried at least 15 different ways, including UTF with/without BOM. Manually adding BOM with System.Text.Encoding.UTF8.GetPreamble(), various MemoryStream, StreamWriter solutions, tried using windows-1252 with CodePagesEncodingProvider.Instance.GetEncoding(1252) but nothing works. When open this file up in Excel the result is always soemthing different than expected.

Anyone that has a solution for this?

Answer 1

Well ,the problem is the way of Excel to deal with BOM . You might found out to use a StreamWriter :

StreamWriter defaults to using an instance of UTF8Encoding unless specified otherwise. This instance of UTF8Encoding is constructed without a byte order mark (BOM), so its GetPreamble method returns an empty byte array. The default UTF-8 encoding for this constructor throws an exception on invalid bytes. This behavior is different from the behavior provided by the encoding object in the Encoding.UTF8 property. To specify a BOM and determine whether an exception is thrown on invalid bytes, use a constructor that accepts an encoding object as a parameter, such as StreamWriter(String, Boolean, Encoding) or StreamWriter.

So I just create a custom implementation of IActionResult :

public class Utf8ForExcelCsvResult : IActionResult
{
    public string Content{get;set;}
    public string ContentType{get;set;}
    public string FileName {get;set;}
    public Task ExecuteResultAsync(ActionContext context)
    {
        var Response =context.HttpContext.Response;
        Response.Headers["Content-Type"] = this.ContentType;
        Response.Headers["Content-Disposition"]=$"attachment; filename={this.FileName}; filename*=UTF-8''{this.FileName}";
        using(var sw = new StreamWriter(Response.Body,System.Text.Encoding.UTF8)){
            sw.Write(Content);
        }
        return Task.CompletedTask ;
    }
}

When you need open such a csv file using Excel , simply return a Utf8ForExcelCsvResult .

[HttpGet]
[Route("/progress/data.csv")]
[Produces("text/csv")]
public IActionResult MyFileDownload()
// public Utf8ForExcelCsvResult MyFileDownload()
{
    StringBuilder sb = new StringBuilder();
    sb.AppendLine("æø;2;3;");
    sb.AppendLine("გამარჯობა");
    sb.AppendLine("ဟယ်လို");
    sb.AppendLine("ສະບາຍດີ");
    sb.AppendLine("cześć");
    sb.AppendLine("こんにちは");
    sb.AppendLine("你好");
    Console.WriteLine(sb.ToString());
    return new Utf8ForExcelCsvResult(){
        Content=sb.ToString(),
        ContentType="text/csv",
        FileName="hello.csv",
    };
}

We can use Powershell to inspect the HEX representation of csv file by Format-hex -path .\\hello.csv :

           00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F

00000000   EF BB BF C3 A6 C3 B8 3B 32 3B 33 3B 0D 0A E1 83  æø;2;3;..á
00000010   92 E1 83 90 E1 83 9B E1 83 90 E1 83 A0 E1 83 AF  ááá á¯
00000020   E1 83 9D E1 83 91 E1 83 90 0D 0A E1 80 9F E1 80  ááá..áá
00000030   9A E1 80 BA E1 80 9C E1 80 AD E1 80 AF 0D 0A E0  áºáá­á¯..à
00000040   BA AA E0 BA B0 E0 BA 9A E0 BA B2 E0 BA 8D E0 BA  ºªàº°àºàº²àºàº
00000050   94 E0 BA B5 0D 0A 63 7A 65 C5 9B C4 87 0D 0A E3  ີ..czeÅ..ã
00000060   81 93 E3 82 93 E3 81 AB E3 81 A1 E3 81 AF 0D 0A  ãã«ã¡ã¯..
00000070   E4 BD A0 E5 A5 BD 0D 0A                          你好..

Here the first three bytes EF BB BF are the Byte order marks