C# 如何在写入之前清除.txt？

我想在我的.txt文件行中删除，但重写不正确。带文本的行会被替换，有时还会重复。 如何在重写opened.txt之前清除它

FileStream fileStream = new FileStream(textBox3.Text,FileMode.OpenOrCreate,
        FileAccess.ReadWrite, FileShare.None);
        string line = null;
        int line_number = 0;
        int line_to_delete = 12;

        using (StreamReader reader = new StreamReader(fileStream))
        {
            using (StreamWriter writer = new StreamWriter(fileStream))
            {
                while ((line = reader.ReadLine()) != null)
                {
                    line_number++;

                    if (line_number == line_to_delete)
                        continue;

                    writer.WriteLine(line);
                }
            }
        }

在我使用下面的代码部分之前，一切都还可以，但是我想读写同一个文件

using (StreamReader reader = new StreamReader(@"C:\Users\user\Desktop\my.txt"))
using (StreamWriter writer = new StreamWriter(@"C:\Users\user\Desktop\my2.txt")) 

---

在FileStream构造函数中使用

FileMode.Truncate

。例如：

FileStream fileStream = new FileStream(textBox3.Text, FileMode.Truncate, FileAccess.ReadWrite, FileShare.None);