C# 读取txt大文件

1GB以下

using System.Text;namespace DotnetReadTxt;class Program
{static void Main(string[] args){try{Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);var gb2312 = Encoding.GetEncoding("GB2312");int index = 0;using (StreamReader sr = new StreamReader("ip20240529.txt",gb2312)){string line;// 逐行读取文件，直到读取完毕  while ((line = sr.ReadLine()) != null){// 在这里处理每一行，例如打印到控制台  index++;if (index < 10){Console.WriteLine(line);}}}Console.WriteLine("读取完毕~~");}catch (Exception e){// 处理可能出现的异常，例如文件不存在或没有读取权限等  Console.WriteLine("The file could not be read:");Console.WriteLine(e.Message);}}/// <summary>/// 获取文本文件的字符编码类型/// </summary>/// <param name="fileName"></param>/// <returns></returns>static Encoding GetTextFileEncodingType(string fileName){Encoding encoding = Encoding.Default;FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read);BinaryReader binaryReader = new BinaryReader(fileStream, encoding);byte[] buffer = binaryReader.ReadBytes((int)fileStream.Length);binaryReader.Close();fileStream.Close();if (buffer.Length >= 3 && buffer[0] == 239 && buffer[1] == 187 && buffer[2] == 191){encoding = Encoding.UTF8;}else if (buffer.Length >= 3 && buffer[0] == 254 && buffer[1] == 255 && buffer[2] == 0){encoding = Encoding.BigEndianUnicode;}else if (buffer.Length >= 3 && buffer[0] == 255 && buffer[1] == 254 && buffer[2] == 65){encoding = Encoding.Unicode;}else if (IsUTF8Bytes(buffer)){encoding = Encoding.UTF8;}return encoding;}/// <summary>/// 判断是否是不带 BOM 的 UTF8 格式/// BOM（Byte Order Mark），字节顺序标记，出现在文本文件头部，Unicode编码标准中用于标识文件是采用哪种格式的编码。/// </summary>/// <param name="data"></param>/// <returns></returns>private static bool IsUTF8Bytes(byte[] data){int charByteCounter = 1; //计算当前正分析的字符应还有的字节数 byte curByte; //当前分析的字节. for (int i = 0; i < data.Length; i++){curByte = data[i];if (charByteCounter == 1){if (curByte >= 0x80){//判断当前 while (((curByte <<= 1) & 0x80) != 0){charByteCounter++;}//标记位首位若为非0 则至少以2个1开始 如:110XXXXX...........1111110X if (charByteCounter == 1 || charByteCounter > 6){return false;}}}else{//若是UTF-8 此时第一位必须为1 if ((curByte & 0xC0) != 0x80){return false;}charByteCounter--;}}if (charByteCounter > 1){throw new Exception("非预期的byte格式");}return true;}
}

1GB以上

ReadTxtFileLine.cs

using System.Text;namespace DotnetReadTxt;/// <summary>
/// 本类用于使用StreamReader.Read()方法，实现逐行读取文本文件，
/// </summary>
public class ReadTxtFileLine
{//文件读取的状态，当为false时，代表未读完最后一行，true为读完了最后一行int _IsReadEnd = 0;System.IO.StreamReader sr1;int _LoopRowNumNow = 0;//定义了一个是否读到最后的属性，数据类型为整数，大于0未读到，等于0是表示末尾了public int IsReadEnd{get => _IsReadEnd;}//构造函数public ReadTxtFileLine(string TxtFilePath, Encoding FileEncoding){sr1 = new System.IO.StreamReader(TxtFilePath, FileEncoding);_IsReadEnd = 1;}//成员方法，执行一次，返回1行的结果，当全部读完，依然执行该方法，将返回空字符串""public string GetLineStr(){string strLine = "";int charCode = 0;while (sr1.Peek() > 0){charCode = sr1.Read();if (charCode == 10) //发现换行符char10就返回拼接字符串{_LoopRowNumNow++;return strLine;}else{if (charCode != 13){//将一行的数据重新拼接起来strLine += ((char)charCode).ToString();}}}_IsReadEnd = -1;sr1.Close();sr1.Dispose();return strLine;}
}

使用

static void Main(string[] args){try{Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);var gb2312 = Encoding.GetEncoding("GB2312");ReadTxtFileLine ReadTxtFileTest1 = new ReadTxtFileLine("ip20240529.txt", gb2312);int index = 0;while (ReadTxtFileTest1.IsReadEnd>0){//这里将读出来的1行赋值给strstring str = ReadTxtFileTest1.GetLineStr();index++;if (index < 10){Console.WriteLine(str);}}Console.WriteLine("读取完毕~~");}catch (Exception e){// 处理可能出现的异常，例如文件不存在或没有读取权限等  Console.WriteLine("The file could not be read:");Console.WriteLine(e.Message);}}