为什么在CH375复位一个StreamReader不允许重新读取UTF8字符串？ [英] Why does reseting a StreamReader does not allow to re-read string in UTF8?

问题描述

正在重置一个StreamReader导致奇怪的行为。第一个断言成功，而第二次失败。要纠正它一（坏的）解决方案包括在CH375复位到位置3，而不是0：sr.BaseStream.Position = 3;

<预类=郎HTML prettyprint-覆盖 > 使用（VAR SR =新的StreamReader（@C：\temp\test.txt，Encoding.UTF8））// test.txt的在UTF8
编码{
VAR读= sr.ReadLine（）;
Assert.AreEqual（FROMFILE，读）; // OK
sr.BaseStream.Position = 0;
sr.DiscardBufferedData（）;
读= sr.ReadLine（）;
Assert.AreEqual（FROMFILE，读）; //失败
}


解决方案

您刚才没T设法的真正的重置对象。有名为类 _checkPreamble 私有字段。它将被设置为假的，因为它已经被选中。你可以破解它：

 使用的System.Reflection; 
 ... 
 VAR网络= typeof运算（的StreamReader）.GetField（_ checkPreamble，BindingFlags.NonPublic可| BindingFlags.Instance）; 
 fi.SetValue（SR，真）; 
读= sr.ReadLine（）; 
 Assert.AreEqual（FROMFILE，读）; //现在没事了
  

当然，你真的不想写这样的代码中。该解决方案是很琐碎，只需要创建一个新的StreamReader对象。

Reseting a StreamReader leads to strange behaviour. The first assert succeeds whereas the second fails. To correct it one (bad) solution consists in reseting to position 3 instead of 0: sr.BaseStream.Position = 3;

using (var sr = new StreamReader(@"c:\temp\test.txt", Encoding.UTF8)) // test.txt is encoded in UTF8
{
     var read = sr.ReadLine();
     Assert.AreEqual("fromfile", read); // ok
     sr.BaseStream.Position = 0;
     sr.DiscardBufferedData();
     read = sr.ReadLine();
     Assert.AreEqual("fromfile", read); //fails
}

解决方案

You just didn't manage to truly reset the object. There's a private field in the class named _checkPreamble. It will be set to false since it was already checked. You can hack it:

using System.Reflection;
...
     var fi = typeof(StreamReader).GetField("_checkPreamble", BindingFlags.NonPublic | BindingFlags.Instance);
     fi.SetValue(sr, true);
     read = sr.ReadLine();
     Assert.AreEqual("fromfile", read); // okay now

Of course you don't really want to write code like this. The solution is very trivial, just create a new StreamReader object.

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