写大文件-txt

最好不把所有的字符组装成string再写，这样极慢并且占用内存。最好使用stream来进行读写。速度快内存小，并且随时序列化了。

class Program
{
    static void Main(string[] args)
    {
        string resultFileName = "c:/168.csv";
        if (!System.IO.Directory.Exists(System.IO.Path.GetDirectoryName(resultFileName)))
        {
            System.IO.Directory.CreateDirectory(System.IO.Path.GetDirectoryName(resultFileName));
        }

        FileStream fs = new FileStream(resultFileName, FileMode.Create);
        StreamWriter sw = new StreamWriter(fs);

        string sb = "";
        string line = "";
        for (long i = 0; i < 100000000; i++)
        {
            if (i % 1000 == 0 && i > 0)
            {
                line = line + i + "\r\n";
                sw.Write(line);
                //sb += line;
                line = "";
            }
            line += i + ",";
        }
        sw.Write(sb);
        sw.Close();
        fs.Close();
    }
}