File FileStream StreamReader和StreamWriter

File 静态类 ReadAllBytes 和 WriteAllBytes ，用于一次性全部读取和写入小文件的字节码，
                  ReadLine  ReadkAll  用于一次性全部读取字符（字符串）
FileStream 采用流的方式，适用于读取任意大小的文件的字节码,

static void CopyAvi(string source, string target)
        {
            using (FileStream fsReader = new FileStream(source, FileMode.OpenOrCreate, FileAccess.Read))
            {
                using (FileStream fsWriter = new FileStream(target, FileMode.OpenOrCreate, FileAccess.Write))
                {
                    byte[] buffer = new byte[1024 * 1024 * 5];
                    while (true)
                    {
                        int length=  fsReader.Read(buffer, 0, buffer.Length);
                        if (length <= 0)
                        {
                            break;
                        }
                        fsWriter.Write(buffer, 0, length);
                    }
                }
            }
        }

StreamReader和StreamWriter 采用流的方式，用于任意大小文件的字符操作

    static void StreamReaderMethod(string path)
        {
            using (StreamReader sr = new StreamReader(path, Encoding.UTF8)) {
                while (!sr.EndOfStream) {
                    Console.WriteLine( sr.ReadLine());
                }
            }
        }

        static void StreamWriterMethod(string path) {
            using (StreamWriter sw = new StreamWriter(path))
            {
                sw.WriteLine("看看有没有覆盖");
            }
        }