url: http://www.cnblogs.com/zhxhdean/archive/2012/02/20/2359605.html

StreamReader,StreamWriter,StringReader,StringWriter每次看到这几个词的时候，就会混淆（理解不够深刻），在使用过程中也经常犯浑，为了能更好的理解，写下此文章。

正文

概念

首先，从字面可以看出，StreamReader,StringReader是用来读操作，StreamWriter,StringWriter是用来写操作。

接下来看这几个类在类库中的层次

上图中，StreamReader,StringReader都派生自TextReader类（TextReader：表示可读取连续字符序列的读取器。抽象基类）

StreamReader从流中读取字符

StringReader从字符串读取字符

上图中，StreamWriter,StringWriter派生自TextWriter类（TextWriter：表示可以编写一个有序字符序列的编写器。该类为抽象类。）

StreamWriter将字符写入流

StringWriter将字符写入字符串

代码

reader操作

        private static void StringRead()
        {
            string in_str ="流操作，字符操作，io操作";
            string read_str, aParagraph = null;
            StringReader sr = new StringReader(in_str);
            while (true)
            {
                read_str = sr.ReadLine();
                if (read_str != null)
                {
                    aParagraph = aParagraph + in_str + " ";
                }
                else
                {
                    aParagraph = aParagraph + "\n";
                    break;
                }
            }
        }

        private static void StreamRead()
        {
            Stream rStream = new FileStream(@"E:/20120214.txt", FileMode.Open);
            StreamReader sr = new StreamReader(rStream, Encoding.UTF8);
            //从流中读取字符
            string result = sr.ReadToEnd();
            //释放资源
            sr.Close();
            rStream.Close();
        }

writer操作

        private static void StreamWriter()
        {
            string in_str = DateTime.Now.ToString("MM-dd HH:mm:ss:fff");
            //第二个参数  是否追加
            StreamWriter sw = new StreamWriter(@"E:/20120214.txt",true,Encoding.Default);
            sw.Write(in_str);
            sw.Flush();
            sw.Close();
        }
        
        private static void StringWriter()
        {            
            StringWriter sw = new StringWriter();
            sw.Write("文字，学习，文字，c#");
            sw.Close();
        }