Question

我对C＃中的文件有点新，我遇到了问题。从文件读取并复制到另一个文件时，最后一块文本没有被写入。以下是我的代码：

StringBuilder sb = new StringBuilder(8192);
string fileName = "C:...rest of path...inputFile.txt";
string outputFile = "C:...rest of path...outputFile.txt";

using (StreamReader reader = File.OpenText(fileName))
{
   char[] buffer = new char[8192];
   while ((reader.ReadBlock(buffer, 0, buffer.Length)) != 0)
   {
      foreach (char c in buffer)
      {
         //do some function on char c... 
         sb.Append(c);
      }

      using (StreamWriter writer = File.CreateText(outputFile))
      {
         writer.Write(sb.ToString());
      }
   }
}

我的目标是以缓冲方式读取和写入文本文件。 Java中我将以下列方式实现的东西：

public void encrypt(File inputFile, File outputFile) throws IOException
{
   BufferedReader infromfile = null;
   BufferedWriter outtofile = null;

   try
   {
      String key = getKeyfromFile(keyFile);
      if (key != null)
      {
         infromfile = new BufferedReader(new FileReader(inputFile));
         outtofile = new BufferedWriter(new FileWriter(outputFile));
         char[] buffer = new char[8192];
         while ((infromfile.read(buffer, 0, buffer.length)) != -1)
         {
            String temptext = String.valueOf(buffer);
            //some changes to temptext are done
            outtofile.write(temptext);
         }
      }
   }
   catch (FileNotFoundException exc)
   {
   } // and all other possible exceptions
}

你能帮我辨别出问题的根源吗？

如果您认为可能有更好的方法来实现文本文件的缓冲i / o，我将非常感谢您的建议。

Answer 1

有几个“陷阱”：

c无法更改（它是foreach迭代变量），您需要复制它才能在编写之前进行处理
你必须跟踪缓冲区的大小，ReadBlock用字符填充它会使你的输出变脏

像这样更改代码看起来很有效：

//extracted from your code
foreach (char c in buffer)
{
    if (c == (char)0) break; //GOTCHA #2: maybe you don't want NULL (ascii 0) characters in your output

    char d = c; //GOTCHA #1: you can't change 'c'

    // d = SomeProcessingHere();

    sb.Append(d);
}

Answer 2

试试这个：

        string fileName = @"";
        string outputfile = @"";

        StreamReader reader = File.OpenText(fileName);
        string texto = reader.ReadToEnd();

        StreamWriter writer = new StreamWriter(outputfile);
        writer.Write(texto);

        writer.Flush();
        writer.Close();

Answer 3

如果你不关心回车，你可以使用File.ReadAllText

此方法打开一个文件，读取文件的每一行，然后将每一行添加为字符串的元素。然后它关闭文件。一行被定义为一系列字符，后跟一个回车符（'\ r'），一个换行符（'\ n'）或一个回车符后面紧跟一个换行符。结果字符串不包含终止回车符和/或换行符。

StringBuilder sb = new StringBuilder(8192);
string fileName = "C:...rest of path...inputFile.txt";
string outputFile = "C:...rest of path...outputFile.txt";

// Open the file to read from.
string readText = File.ReadAllText(fileName );
foreach (char c in readText)
{
   // do something to c
   sb.Append(new_c);
}

// This text is added only once to the file, overwrite it if it exists
File.WriteAllText(outputFile, sb.ToString());

Answer 4

这对你有用吗？

       using (StreamReader reader = File.OpenText(fileName))
       {
            char[] buffer = new char[8192];
            bool eof = false;

            while (!eof)
            {
                int numBytes = (reader.ReadBlock(buffer, 0, buffer.Length));
                if (numBytes>0)
                {
                    using (StreamWriter writer = File.CreateText(outputFile))
                    {
                        writer.Write(buffer, 0, numBytes);
                    }
                } else {
                    eof = true;
                }

            }
        }

你仍然需要处理字符编码！

Answer 5

除非我遗漏了某些内容，否则您的问题似乎是您在每次blockread迭代时都覆盖了输出文件的现有内容。

你打电话：

  using (StreamWriter writer = File.CreateText(outputFile))
  {
     writer.Write(sb.ToString());
  }

每次ReadBlock迭代。该文件的输出只是读取的最后一块数据。

来自File.CreateText上的MSDN文档：

如果path指定的文件不存在，则创建该文件。如果文件确实存在，其内容被覆盖。

读取和写入文本文件时出现意外输出

5 个答案: