C# Streamwriter – Problem with the encoding

April 14, 2022

I have some product data that I want to write into a csv file. First I have a function that writes the header into the csv file:

using(StreamWriter streamWriter = new StreamWriter(path))
{
    string[] headerContent = {"banana","apple","orange"};
    string header = string.Join(",", headerContent);
    streamWriter.WriteLine(header);
}

Another function goes over the products and writes their data into the csv file:

using (StreamWriter streamWriter = new StreamWriter(new FileStream(path, FileMode.Open), Encoding.UTF8))
{
    foreach (var product in products)
    {
        await streamWriter.WriteLineAsync(product.ToString());
    }
}

When writing the products into the csv file and do it with FileMode.Open and Encoding.UTF8, the encoding is set correctly into the file meaning that special characters in german or french get shown correctly. But the problem here is that I overwrite my header when I do it like this.

The solution I tried was to not use FileMode.Open but to use FileMode.Append which works, but then for some reason the encoding just gets ignored.

What could I do to append the data while maintaing the encoding? And also why is this happening in the first place?

EDIT:

Example with FileMode.Open:

Fußpflegecreme

Example with FileMode.Append:

FuÃŸpflegecreme