在C#中读取和写入非常大的文本文件 [英] Reading and writing very large text files in C#

问题描述

我有一个非常大的文件，大小将近2GB.我正在尝试编写一个过程来读入文件并将其写出而没有第一行.我几乎只能一次只能读和写一行，这需要永远的时间.我可以打开它，删除第一行并在TextPad中更快地保存它，尽管那仍然很慢.

I have a very large file, almost 2GB in size. I am trying to write a process to read the file in and write it out without the first row. I pretty much have been only able to read and write one line at a time which takes forever. I can open it, remove the first row and save it faster in TextPad, though that is still very slow.

我使用以下代码获取文件中的记录数:

I use this code to get the number of records in the file:

private long getNumRows(string strFileName)
{
    long lngNumRows = 0;
    string strMsg;

    try
    {
        lngNumRows = 0;
        using (var strReader = File.OpenText(@strFileName))
        {
            while (strReader.ReadLine() != null)
            {
                lngNumRows++;
            }

            strReader.Close();
            strReader.Dispose();
        }
    }
    catch (Exception excExcept)
    {
        strMsg = "The File could not be read: ";
        strMsg += excExcept.Message;
        System.Windows.MessageBox.Show(strMsg);
        //Console.WriteLine("Thee was an error reading the file: ");
        //Console.WriteLine(excExcept.Message);

        //Console.ReadLine();
    }

    return lngNumRows;
}

这仅需几秒钟即可运行.当我添加以下代码时，它将永远运行.难道我做错了什么?为什么写会增加这么多时间?关于如何使此速度更快的任何想法?

This only takes seconds to run. When I add the following code it takes forever to run. Am I doing something wrong? Why does the write add so much time? Any ideas on how I can make this faster?

private void ProcessTextFiles(string strFileName)
{
    string strDataLine;
    string strFullOutputFileName;
    string strSubFileName;
    int intPos;
    long lngTotalRows = 0;
    long lngCurrNumRows = 0;
    long lngModNumber = 0;
    double dblProgress = 0;
    double dblProgressPct = 0;
    string strPrgFileName = "";
    string strOutName = "";
    string strMsg;
    long lngFileNumRows;

    try
    {
       using (StreamReader srStreamRdr = new StreamReader(strFileName))
        {
            while ((strDataLine = srStreamRdr.ReadLine()) != null)
            {
                lngCurrNumRows++;

                if (lngCurrNumRows > 1)
                {
                    WriteDataRow(strDataLine, strFullOutputFileName);
                }
            }

            srStreamRdr.Dispose();
        }
    }
    catch (Exception excExcept)
    {
        strMsg = "The File could not be read: ";
        strMsg += excExcept.Message;
        System.Windows.MessageBox.Show(strMsg);
        //Console.WriteLine("The File could not be read:");
        //Console.WriteLine(excExcept.Message);
    }
}

public void WriteDataRow(string strDataRow, string strFullFileName)
{
    //using (StreamWriter file = new StreamWriter(@strFullFileName, true, Encoding.GetEncoding("iso-8859-1")))
    using (StreamWriter file = new StreamWriter(@strFullFileName, true, System.Text.Encoding.UTF8))
    {
        file.WriteLine(strDataRow);
        file.Close();
    }
}

推荐答案

不确定这将提高性能多少，但可以肯定的是，为要编写的每一行打开和关闭输出文件并不是一个好主意.

Not sure how much this will improve the performance, but surely, opening and closing the output file for every line that you want to write is not a good idea.

相反只打开两个文件，然后直接写一行

Instead open both files just one time and then write the line directly

using (StreamWriter file = new StreamWriter(@strFullFileName, true, System.Text.Encoding.UTF8))
using (StreamReader srStreamRdr = new StreamReader(strFileName))
{
    while ((strDataLine = srStreamRdr.ReadLine()) != null)
    {
        lngCurrNumRows++;

        if (lngCurrNumRows > 1)
           file.WriteLine(strDataRow);
    }
}

您还可以取消对 lngCurrNumRow 的检查，只需在进入while循环之前进行空读取

You could also remove the check on lngCurrNumRow simply making an empty read before entering the while loop

strDataLine = srStreamRdr.ReadLine();
if(strDataLine != null)
{
    while ((strDataLine = srStreamRdr.ReadLine()) != null)
    {
           file.WriteLine(strDataRow);
    }
}

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