.net I/O操作 导图

稍微总结下，System.IO提供了四种类型来实现，对单个文件和计算机目录结构的操作。Directory和File通过静态成员实现建立、删除、复制和移动操作（上图没有提及）。而FileInfo和DirectryInfo类型则通过实例级方法来实现类似的功能，并且更加推荐使用，原因是它们的成员方法返回强类型的对象。

FileStream和StreamReader/StreamWriter的主要区别在于，FileStream操作的是字节/字节数组；而StreamReader/StreamWriter可以操作字符串。

public  void CreateByteFile()
{
    var fileInfo = new FileInfo(string.Format(@"{0}\Test.dat", Environment.CurrentDirectory));
    using (var fileStream = fileInfo.Open(FileMode.OpenOrCreate,FileAccess.ReadWrite,FileShare.None))
    {
        const string msg = "Hello";
        var msgAsByteArray = Encoding.Default.GetBytes(msg);
        fileStream.Write(msgAsByteArray,0,msgAsByteArray.Length);
        fileStream.Position = 0;
        Console.WriteLine("Your Message as an array of bytes:\n");
        var bytesFormFile = new byte[msgAsByteArray.Length];
        for (var i = 0; i < msgAsByteArray.Length; i++)
        {
            bytesFormFile[i] =(byte) fileStream.ReadByte();
            Console.WriteLine(bytesFormFile[i]);
        }
        Console.WriteLine("\n Decoded Message: ");
        Console.WriteLine(Encoding.Default.GetString(bytesFormFile));
    }
}

public void WriteCharFile()
{
    var fileInfo = new FileInfo(string.Format( "{0}reminders.txt", AppDomain.CurrentDomain.BaseDirectory));
    using (var streamWriter = fileInfo.CreateText())
    {
        streamWriter.WriteLine("Don't forget Mother's Day this year...");
        streamWriter.WriteLine("Don't forget Father's Day this year...");
        streamWriter.WriteLine("Don't forget These numbers:");
        for (var i = 0; i < 10; i++)
        {
                streamWriter.Write(i + "    ");
        }
        streamWriter.Write(streamWriter.NewLine);
    }
    Console.WriteLine("Created file and wrote some thoughts...");
    Console.ReadKey();
}

StringBuilder,StringWriter,String差异与用途

总觉得，他们很像，感觉做的事情很像，所以查了一下。

1.用Reflector反射看了下StringWriter，发现其还是用StringBuilder干事情。下面是他的Write方法。他里边使用了StringBuilder类的全局变量。同时，他还提供了GetStringBuilder方法，通过这个方法可以获取这个全局变量

private StringBuilder _sb;

public override void Write(string value)
{
    if (!this._isOpen)
    {
        __Error.WriterClosed();
    }
    if (value != null)
    {
        this._sb.Append(value);
    }
}
StringWriter和StringBuilder的最大差异在于StringWriter继承于TextWriter。可以将StringWriter简单理解为内部存储使用StringBuiler的一个TextWriter的实现类。这样你就可以通过StringWriter来使用TestWriter的API了。（MSDN的神解释：A StringWriter is simply an implementation of TextWriter that uses a StringBuilder internally for storage. So you use StringWriter with APIs that operate on TextWriters.）

2. StringWriter，StringBuilder的另一种描述

StringWriter derives from TextWriter, which allows various classes to write text without caring where it's going. In the case of StringWriter, the output is just into memory. You would use this if you're calling an API which needs a TextWriter but you only want to build up results in memory.

StringBuilder is essentially a buffer which allows you to perform multiple operations (typically appends) to a "logical string" without creating a new string object each time. You would use this to construct a string in multiple operations.

3.StringBuilder，String差异

String 对象串联操作总是用现有字符串和新数据创建新的对象。

StringBuilder 对象维护一个缓冲区，以便容纳新数据的串联。 如果房间可用，新数据追加到缓冲区；否则，新的分配，较大的缓冲区，从原始缓冲区的数据复制到新的缓冲区，并且，新数据并追加到新的缓冲区。

串联操作的性能 String 或 StringBuilder 对象的取决于内存分配的频率。String 串联运算始终分配内存，而 StringBuilder串联运算分配内存，仅当 StringBuilder 对象缓冲区因过小而无法适应新数据。

如果是连接固定的数量的string字符串，建议使用string连接（Use the String class if you are concatenating a fixed number of String objects）。在这种情况下，编译器可能甚至合并单个的串联运算到单个操作（In that case, the compiler may even combine individual concatenation operations into a single operation.）。使用一 StringBuilder 对象是否连接任意字符串；例如，在中，如果使用循环连接随机数用户输入字符串。（Use a StringBuilder object if you are concatenating an arbitrary number of strings; for example, if you're using a loop to concatenate a random number of strings of user input）